View AD7998_264792.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

PRELIMINARYTECHNICAL DATA
a
8 Channel, 12-/10-Bit ADCs with I2C Compatible Interface in 20-Lead TSSOP AD7998/AD7997 Preliminary Technical Data
FUNCTIONAL BLOCK DIAGRAM
VDD GND REFIN CONVST
FEATURES 12-Bit ADC with Fast Conversion Time: 2 s Eight Single-Ended Analog Input Channels Specified for VDD of 2.7 V to 5.5 V Low Power Consumption Fast Throughput Rate:- 188 KSPS Sequencer Operation Automatic Cycle Mode I2CR Compatible Serial Interface I2CR Interface supports: Standard, Fast, and High-Speed Modes Out of Range Indicator Alert Function Pin-Selectable Addressing via AS Two Versions Allow Five I2C Addresses Shutdown Mode: 1A max 20-Lead TSSOP Package GENERAL DESCRIPTION
AD7998/AD7997
VIN1 8:1 I/P MUX VIN8 T/H 12-/10-BIT SUCCESSIVE APPROXIMATION ADC CONTROL LOGIC
OSCILLATOR
DATALOW LIMIT REGISTER CH1-CH4
CONVERSION RESULT REGISTER CONFIGURATION REGISTER ALERT STATUS REGISTER CYCLE TIMER REGISTER I2C INTERFACE SCL SDA ALERT
DATAHIGH LIMIT REGISTER CH1-CH4
HYSTERESIS REGISTER CH1-CH4 AS
The AD7998/AD7997 are 8 channel, 12-/10-bit, high speed, low power, successive-approximation ADCs respectively. The parts operate from a single 2.7 V to 5.5 V power supply and feature a conversion time of 2 s. The parts contain an eight channel multiplexer and track/hold amplifier which can handle input frequencies in excess of TBD kHz. The AD7998/AD7997 provide a two-wire serial interface which is compatible with I2C interfaces. Each part come in two versions, AD7998-0/AD7997-0 to AD7998-1/ AD7997-1. Each version allows for a minimum of two different I2C addresses. The I2C interface on the AD79980/AD7997-0 supports Standard and Fast I2C Interface Modes. The I2C Interface on the AD7998-1/AD7997-1 supports Standard, Fast and two High-Speed I2C Interface Modes. The AD7998/AD7997 normally remain in a shutdown state while not converting, powering up only for conversions. The conversion process can be controlled using the CONVST pin, an Automatic Conversion Cycle selected through software control, or a mode where conversions occur across read Address operations. There are no pipeline delays associated with the part. The reference for the part is applied externally to the REFIN pin and can be in the range of 1.2V to VDD. This allows the widest dynamic input range to the ADC.
GND
On-chip registers can be programmed with high and low limits for the conversion result, and an open drain Out of Range Indicator output (ALERT), becomes active when the programmed high or low limits are violated by the conversion result. This output can be used as an interrupt.
PRODUCT HIGHLIGHTS
1. 2 s Conversion time with low power consumption. 2. I2C Compatible Serial Interface with pin selectable addresses. Two AD7998/AD7997 versions allow five AD7998/AD7997 devices to be connected to the same serial bus. 3. The parts feature automatic shutdown while not converting to maximize power efficiency. Current consumption is 1A max when in shutdown. 4. Reference can be driven up to the power supply. 5. Out of Range Indicator which can be software disabled/ enabled. 6. Oneshot and automatic conversion rates. 7. No Pipeline Delay The part features a standard successive-approximation ADC.
SMBus is a trademark and I2C is a registered trademark of Philips Corporation
REV. PrB
11/02
One Technology Way, P Box 9106, Norwood, MA 02062-9106, U.S.A. .O. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2002
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
PRELIMINARYTECHNICAL DATA
AD7998-SPECIFICATIONS1 otherwise noted; T = T
Parameter DYNAMIC PERFORMANCE Signal to Noise + Distortion (SINAD)2 Signal to Noise Ratio (SNR)2 Total Harmonic Distortion (THD)2 Peak Harmonic or Spurious Noise (SFDR)2 Intermodulation Distortion (IMD)2 Second Order Terms Third Order Terms Aperture Delay Aperture Jitter Channel-to-Channel Isolation Full Power Bandwidth DC ACCURACY Resolution Integral Nonlinearity2 Differential Nonlinearity2 Offset Error2 Offset Error Match2 Gain Error2 Gain Error Match2 ANALOG INPUT Input Voltage Ranges DC Leakage Current Input Capacitance REFERENCE INPUT REFIN Input Voltage Range DC Leakage Current Input Capacitance Input Impedance LOGIC INPUTS (SDA, SCL, CONVST) Input High Voltage, VINH Input Low Voltage, VINL Input Leakage Current, IIN Input Capacitance, CIN2,3 Input Hysteresis, VHYST LOGIC OUTPUTS (SDA) Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance2,3 Output Coding LOGIC OUTPUTS (ALERT) Output High Voltage, VOH Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance2,3 CONVERSION RATE Conversion Time Track/Hold Acquisition Time Throughput Rate B Version1 70 71 -78 -80 -78 -78 10 10 TBD TBD TBD 12 1 0.6 +1.5/-0.9 0.75 1.5 0.5 1.5 0.5 0 to REFIN 1 30 1.2 to VDD 1 TBD TBD 0.7(V DD ) 0.3(V DD ) 1 10 TBD dB dB dB dB
(VDD = +2.7 V to +5.5 V, unless otherwise noted ; REFIN = 2.5 V; fSCL = 3.4 MHz unless A MIN to TMAX, unless otherwise noted.)
Units min min typ typ fa = TBD kHz, fb = TBD kHz dB typ dB typ ns max ps typ dB typ kHz typ kHz typ Bits LSB LSB LSB LSB LSB LSB LSB LSB Test Conditions/Comments FIN = 10kHz Sine Wave
FIN = TBD kHz @ 3 dB @ 0.1 dB
max typ max typ max max max max
Guaranteed No Missed Codes to 12 Bits.
Volts A max pF typ V min/Vmax A max pF max k typ V min V max A max pF max V min
VIN = 0 V or VDD
0.4 V max 0.6 V max 1 A max TBD pF max Straight (Natural) Binary
ISINK = 3mA ISINK = 6mA
V DD -0.2 0.4 1 TBD
V min V max A max pF max
ISOURCE = 200 A, VDD =2.7 to 5.5V ISINK = 200 A
See Interface Section TBD TBD TBD 3.4 13 79 -2- s max ns max ns max KSPS max KSPS max KSPS max . Full-Scale step input Sine wave input <= 30 Standard mode SCL = Fast Mode SCL = 400 High-Speed Mode SCL
KHz 100 kHz kHz = 3.4 MHz REV. PrB
PRELIMINARYTECHNICAL DATA
V to noted ; REF = AD7998-SPECIFICATIONS1 (V = +2.7noted;+5.5 TV, unless otherwiseotherwise noted.)2.5 V; f otherwise T= to T , unless
DD IN A MIN MAX SCL
= 3.4 MHz unless
Parameter POWER REQUIREMENTS VDD IDD Peak Current Power Down Mode , Interface Inactive Interface Active
B Version1 2.7/5.5 TBD TBD TBD TBD TBD TBD TBD TBD TBD
Units V min/max A A A A A A A A A max max max max max max max max max
Test Conditions/Comments
Digital Inputs = 0 V or VDD Peak Current during conversion VDD = 2.7 to 3.6 V. VDD = 4.75 to 5.5 V. VDD = 2.7 to 3.6 V. VDD = 4.75 to 5.5 V. VDD VDD VDD VDD = = = = 2.7 to 3.6 V. 4.75 to 5.5 V. 2.7 to 3.6 V. 4.75 to 5.5 V.
Operating, Interface Inactive Interface Active
NOTES 1 Temperature ranges as follows: B Version: -40C to +85C. 2 See Terminology. 3 Sample tested @ +25C to ensure compliance. 4 See POWER VERSUS THROUGHPUT RATE section. Specifications subject to change without notice.
-3-
REV. PrB
PRELIMINARYTECHNICAL DATA
V to noted ; REF = AD7997-SPECIFICATIONS1 (V = +2.7noted;+5.5 TV, unless otherwiseotherwise noted.)2.5 V; f otherwise T= to T , unless
DD IN A MIN MAX SCL
= 3.4 MHz unless
Parameter DYNAMIC PERFORMANCE Signal to Noise + Distortion (SINAD)2 Signal to Noise Ratio (SNR)2 Total Harmonic Distortion (THD)2 Peak Harmonic or Spurious Noise (SFDR)2 Intermodulation Distortion (IMD)2 Second Order Terms Third Order Terms Aperture Delay Aperture Jitter Channel-to-Channel Isolation Full Power Bandwidth DC ACCURACY Resolution Integral Nonlinearity2 Differential Nonlinearity 2 Offset Error2 Offset Error Match2 Gain Error2 Gain Error Match2 Total Unadjusted Error (TUE)2 ANALOG INPUT Input Voltage Ranges DC Leakage Current Input Capacitance REFERENCE INPUT REFIN Input Voltage Range DC Leakage Current Input Capacitance Input Impedance LOGIC INPUTS (SDA, SCL, CONVST) Input High Voltage, VINH Input Low Voltage, VINL Input Leakage Current, IIN Input Capacitance, CIN2,3 Input Hysteresis, VHYST LOGIC OUTPUTS (SDA) Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance2,3 Output Coding LOGIC OUTPUTS (ALERT) Output High Voltage, VOH Output Low Voltage, VOL Floating-State Leakage Current Floating-State Output Capacitance2,3 CONVERSION RATE Conversion Time Track/Hold Acquisition Time Throughput Rate
B Version1 61 TBD -73 -74 -78 -78 10 10 TBD TBD TBD 10 1 0.6 0.9 1 0.5 1 0.5 1 0 to REFIN 1 30 1.2 to VDD 1 TBD TBD 0.7(V DD ) 0.3(V DD ) 1 10 TBD
Units dB dB dB dB min min typ typ
Test Conditions/Comments FIN = 10kHz Sine Wave
fa = TBD kHz, fb = TBD kHz dB typ dB typ ns max ps typ dB typ kHz typ kHz typ Bits LSB max LSB typ LSB max LSB LSB LSB LSB LSB max max max max max
FIN = TBD kHz @ 3 dB @ 0.1 dB
Guaranteed No Missed Codes to 10 Bits.
Volts A max pF typ V min/Vmax A max pF max k typ V min V max A max pF max V min
VIN = 0 V or VDD
0.4 V max 0.6 V max 1 A max TBD pF max Straight (Natural) Binary 2.4 0.4 1 TBD V min V max A max pF max
ISINK = 3mA ISINK = 6mA
ISOURCE = 200 A VDD =2.7 to 5.5V ISINK = 200 A
See Interface Section TBD TBD TBD 3.4 13 79 -4- s max ns max ns max KSPS max KSPS max KSPS max Full-Scale step input Sine wave input <= 30 KHz Standard mode 100 kHz Fast Mode 400 kHz High-Speed Mode 3.4 MHz REV. PrB
PRELIMINARYTECHNICAL DATA
AD7997-SPECIFICATIONS1 otherwise noted; T = T
Parameter POWER REQUIREMENTS VDD IDD Peak Current Power Down Mode , Interface Inactive Interface Active B Version1
(VDD = +2.7 V to +5.5 V, unless otherwise noted ; REFIN = 2.5 V; fSCL = 3.4 MHz unless A MIN to TMAX, unless otherwise noted.)
Units Test Conditions/Comments
2.7/5.5 V min/max TBD TBD TBD TBD TBD TBD TBD TBD TBD A A A A A A A A A max max max max max max max max max Digital Inputs = 0 V or VDD Peak Current during conversion VDD = 2.7 to 3.6 V. VDD = 4.75 to 5.5 V. VDD = 2.7 to 3.6 V. VDD = 4.75 to 5.5 V. VDD VDD VDD VDD = = = = 2.7 to 3.6 V. 4.75 to 5.5 V. 2.7 to 3.6 V. 4.75 to 5.5 V.
Operating, Interface Inactive Interface Active
NOTES 1 Temperature ranges as follows: B Version: -40C to +85C. 2 See Terminology. 3 Sample tested @ +25C to ensure compliance. 4 See POWER VERSUS THROUGHPUT RATE section. Specifications subject to change without notice.
t11 t2
t12
t6
SCL t6 t4 t1 t10 SDA t7 P S S P t3 t5 t8 t9
S = START CONDITION P = STOP CONDITION
Figure 1. Two-Wire Serial Interface Timing Diagram
I2C TIMING SPECIFICATIONS1
Parameter fSCL
2
(VDD = +2.7 V to +5.5 V, unless otherwise noted ; REFIN = 2.5 V; unless otherwise noted; TA = TMIN to TMAX, unless otherwise noted..)
AD7998/AD7997 Limit at TMIN, TMAX MIN MAX Unit 100 400 3.4 1.7 4 0.6 60 120 4.7 1.3 160 320 250 100 10 -5- kHz kHz MHz MHz ms ms ns ns ms ms ns ns ns ns ns
Conditions Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode Fast Mode High-Speed Mode
Description Serial Clock Frequency
CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max
t1
tHIGH, SCL High Time
t2
tLOW, SCL Low Time
t3
-
tSU;DAT, Data Setup Time
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997 I2C TIMING SPECIFICATIONS1 (Continued.)
Parameter Conditions t4 Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode t5 Fast Mode High-Speed Mode Standard Mode t6 Fast Mode High-Speed Mode Standard Mode t7 Fast Mode t8 Standard Mode Fast Mode High-Speed Mode Standard Mode t9 Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode t 10 Fast Mode High-Speed Mode, High-Speed Mode, t 11 Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, t 11A Standard Mode Fast Mode High-Speed Mode, High-Speed Mode, Standard Mode t 12 Fast Mode High-Speed Mode, High-Speed Mode, t SP 4 Fast Mode High-Speed Mode t POWER-UP AD7998/AD7997 Limit at TMIN, TMAX MIN MAX 0 3.45 0 0.9 0 70 0 150 4.7 0.6 160 4 0.6 160 4.7 1.3 4 0.6 160 1000 20 + 0.1CB 300 10 80 20 160 300 20 + 0.1CB 300 10 80 20 160 1000 20 + 0.1CB 300 10 40 20 80 1000 20 + 0.1CB 300 10 80 20 160 300 20 + 0.1CB 300 10 40 20 80 0 50 0 10 1 Unit s s ns ns s s ns s s ns s s s s ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns s Description t HD;DAT, Data Hold Time
CB = 100pF max CB = 400pF max
tSU;STA, Set-up Time for a repeated START Condition t HD;STA, Hold Time (repeated) START Condition tBUF, Bus Free Time Between a STOP and a START Condition. tSU;STO, Set-up Time for STOP Condition tRDA, Rise time of SDA signal
CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max CB = 100pF max CB = 400pF max
tFDA, Fall time of SDA signal
tRCL, Rise time of SCL signal
tRCL1, Rise time of SCL signal after a repeated START Condition and after an Acknowledge bit. tFCL, Fall Time of SCL signal
Pulsewidth of Spike Suppressed. Power-up Time
NOTES 1 See Figure 1. C B refers to the capacitance load on the bus line. Hs-Mode timing specifications apply to the AD7998-1/AD7997-1 only. Standard and Fast Mode timing specifications apply to both the AD7998-0/AD7997-0 and the AD7998-1/AD7997-1. 2 The SDA and SCL timing is measured with the input filters enabled. Switching off the input filters improves the transfer rate but has a negative effect on EMC behavior of the part. 4 Input filtering on both the SCL and SDA inputs suppress noise spikes that are less than 50ns or 10ns for Fast Mode or High-Speed mode respectivley. Specifications subject to change without notice.
-6-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
ABSOLUTE MAXIMUM RATINGS1
(TA = +25C unless otherwise noted)
VDD to GND -0.3 V to 7 V Analog Input Voltage to GND -0.3 V to VDD + 0.3 V Reference Input Voltage to GND -0.3 V to VDD + 0.3 V Digital Input Voltage to GND -0.3 V to 7 V Digital Output Voltage to GND -0.3 V to VDD + 0.3 V Input Current to Any Pin Except Supplies2 10 mA Operating Temperature Range Commercial (B Version) -40C to +85C Storage Temperature Range -65C to +150C
Junction Temperature 20-ld TSSOP Package, JA Thermal Impedance JC Thermal Impedance Lead Temperature, Soldering Vapor Phase (60 secs) Infared (15 secs)
+150C 143C/W (TSSOP) 45C/W (TSSOP) +215C +220C
NOTES 1 Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 Transient currents of up to 100 mA will not cause SCR latch up.
ORDERING GUIDE
Model 1 AD7998BRU-0 AD7998BRU-1 AD7997BRU-0 AD7997BRU-1
Temperature Range -40C -40C -40C -40C to to to to +85C +85C +85C +85C
Linearity Error2(max) 1 1 1 1 LSB LSB LSB LSB
Package Option3 RU-20 RU-20 RU-20 RU-20
NOTES The AD7998-0/AD7997-0 supports Standard and Fast I 2 C Interface Modes. The AD7998-1/AD7997-1 supports Standard, Fast and Highspeed I 2 C Interface modes. 2 Linearity error here refers to Integral Nonlinearity 3 RU = TSSOP.
1
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD7998/AD7997 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
REV. PrB
-7-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
PIN FUNCTION DESCRIPTION
Pin Pin No. Mnemonic 1,3, 4 AGND 2,5 V D D 6 REF IN
Function Analog Ground. Ground reference point for all circuitry on the AD7998/AD7997. All analog input signals should be referred to this GND voltage. Power Supply Input. The VDD range for the AD7998/AD7997 is from +2.7V to +5.5V. Voltage Reference Input. The External Reference for the AD7998/AD7997 should be applied to this input pin. The voltage range for the external Reference is 1.2 V to VDD. A TBD nF capacitor should be placed between the REFIN pin and AGND. Analog Input 1. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 3. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 5. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 7. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 8. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 6. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 4. Single-ended analog input channel. The input range is 0V to REFIN. Analog Input 2. Single-ended analog input channel. The input range is 0V to REFIN. Logic Input. Address Select Input which selects one of three I2C addresses for the AD7998/ AD7997 as shown in Table I. The address selected will depend on the voltage applied to this pin, VDD, AGND, or NC. Logic Input Signal. Convert Start Signal. This is an edge triggered logic input. The rising edge of this signal powers up the part. The power up time for the part is 1s. The falling edge of CONVST places the track/hold into hold mode and initiates a conversion. A power up time of at least 1s must be allowed for the CONVST high pulse, otherwise the conversion result will be invalid. (See Modes of Operation Section) Digital Output, selectable as an ALERT or BUSY output function. When configured as an ALERT, this pin acts as an Out of Range Indicator and if enabled it becomes active when the conversion result violates the DATAHIGH or DATALOW values. See Limit Registers section. When configured as a BUSY output, this pin becomes active when a conversion is in progress. Digital I/O. Serial Bus Bi-directional Data. Open-drain output. External pull-up resistor required. Digital Input. Serial Bus Clock. External pull-up resistor required. No Connect pin.
7 8 9 10 11 12 13 14 15
V IN 1 V IN 3 V IN 5 V IN 7 V IN 8 V IN 6 V IN 4 V IN 2 AS
16
CONVST
17
ALERT/BUSY
18 19 20
SDA SCL NC
AD7998/AD7997 PIN CONFIGURATION TSSOP
AGND VDD AGND AGND VDD REFIN VIN1 VIN3 VIN5 VIN7
1 2 3 4 5 6 7 8 9 10
20
NC SCL SDA
AD7998/ AD7997 TOP VIEW
(Not to Scale)
19 18
17 ALERT 16 CONVST 15 14 AS VIN2
13 VIN4 12 VIN6
11 VIN8
-8-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
Table I. I2C Address Selection
Part Number AD7997-0 AD7997-0 AD7997-1 AD7997-1 AD7997-X 1
AS Pin GND V DD GND V DD Float
I2C Address 010 010 010 010 010 0001 0010 0011 0100 0000
Note :1 If the AS pin is left floating on any of the AD7997 parts the device address will be 010 0000
Part Number AD7998-0 AD7998-0 AD7998-1 AD7998-1 AD7998-X 1
AS Pin GND V DD GND V DD Float
I2C Address 010 010 010 010 010 0001 0010 0011 0100 0000
Note :1 If the AS pin is left floating on any of the AD7998 parts the device address will be 010 0000
REV. PrB
-9-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
TERMINOLOGY
Signal to (Noise + Distortion) Ratio Channel-to-Channel Isolation
This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digitization process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal Nbit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02 N + 1.76) dB Thus for a 12-bit converter, this is 74 dB
Total Harmonic Distortion
Channel-to-Channel Isolation is a measure of the level of crosstalk between channels. It is measured by applying a fullscale TBD kHz sine wave signal to the nonselected input channels and determining how much the TBD kHz signal is attenuated in the selected channel. This figure is
given worse case across all channels.
Aperture Delay This is the measured interval between the leading edge of the sampling clock and the point at which the ADC actually takes the sample. Aperture Jitter This is the sample-to-sample variation in the effective point in time at which the sample is taken. Full Power Bandwidth
The Full Power Bandwidth of an ADC is that input frequency at which the amplitude of the reconstructed Fundamental is reduced by 0.1 dB or 3 dB for a full-scale input PSRR (Power Supply Rejection)
Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7998/ AD7997, it is defined as:
THD (dB ) = 20 log V2 +V3 +V 4 +V5 +V 6 V1
2 2 2 2 2
where V1 is the rms amplitude of the fundamental and V2, V3, V4 , V5 and V6 are the rms amplitudes of the second through the sixth harmonics.
Peak Harmonic or Spurious Noise
The power supply rejection ratio is defined as the ratio of the power in the ADC output at full-scale frequency, f, to the power of a 200 mV p-p sine wave applied to the ADC VDD supply of frequency fs. PSRR (dB) = 10 log (Pf/Pfs) Pf is the power at frequency f in the ADC output; Pfs is the power at frequency fs coupled onto the ADC VDD supply.
Integral Nonlinearity
Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the harmonics are buried in the noise floor, it will be a noise peak.
Intermodulation Distortion
This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1 LSB below the first code transition, and full scale, a point 1 LSB above the last code transition.
Differential Nonlinearity
With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m nor n are equal to zero. For example, the second order terms include (fa + fb) and (fa - fb), while the third order terms include (2fa + fb), (2fa - fb), (fa + 2fb) and (fa - 2fb). The AD7998/AD7997 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified separately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dBs.
This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e AGND + 1LSB
Offset Error Match
This is the difference in offset error between any two channels.
Gain Error
This is the deviation of the last code transition (111 . . . 110) to (111 . . . 111) from the ideal (i.e., REFIN - 1 LSB) after the offset error has been adjusted out. Gain Error Match This is the difference in Gain error between any two channels.
-10-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
AD7998/AD7997 TYPICAL PERFORMANCE CURVES
TPC 1 shows a typical FFT plot for the AD7998 at TBD kSPS sampling rate with a TBD kHz input frequency.
TPC 1. AD7998 Dynamic Performance at TBD ksps.
TPC 2. AD7997 Dynamic Performance at TBD ksps.
TPC 3. PSRR vs Supply Ripple Frequency.
TPC 4. AD7998 SINAD vs Analog Input Frequency for Various Supply Voltages at TBD ksps.
TPC 5. AD7998 Typical INL VDD = 5V.
TPC 6. AD7998 Typical DNL VDD = 5V.
TPC 7. AD7998 Typical INL VDD = 3V.
TPC 8. AD7998 Typical DNL VDD = 3V.
TPC 9. AD7998 Change in INLvs Reference Voltage VDD = 5V.
REV. PrB
-11-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
TPC 10. AD7998 Change in DNL vs Reference Voltage.
TPC 11. AD7998 Shutdown Current vs Supply Voltage, -40 , 25 and 85 C.
TPC 12. AD7998 Supply Current vs I2C Bus Rate for VDD = 3V and 5V.
TPC 13. AD7998 Supply Current vs Supply Voltage for Various Temperatures.
TPC 14. AD7998 ENOB vs Reference Voltage, VDD = 3V and VDD = 5V.
-12-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
CIRCUIT INFORMATION
The AD7998/AD7997 are fast, low-power, 12-/10-bit, single supply, 8 Channel A/D converters respectively. The parts can be operated from a 2.7 V to 5.5 V supply. The AD7998/AD7997 provide the user with an 8-channel multiplexer, an on-chip track/hold, A/D converter, an onchip oscillator, internal data registers and an I2C compatible serial interface, all housed in a 20-lead TSSOP package, which offers the user considerable space saving advantages over alternative solutions. An external reference is required by the AD7998/AD7997, and this reference can be in the range of 1.2 V to VDD. The AD7998/AD7997 will normally remain in a powerdown state while not converting. When supplies are first applied the part will come up in a power-down state. Power-up is intitiated prior to a conversion and the device returns to power-down upon completion of the conversion. Conversions can be initiated on the AD7998/AD7997 by either pulsing the CONVST signal, using an automatic cycling mode or using a mode where wake-up and conversion occur during the read function ( see modes of Operation section). On completion of a conversion the AD7998/ AD7997 will enter shutdown mode again. This automatic shutdown feature allows power saving between conversions. This means any read or write operations across the I2C interface can occur while the device is in shutdown.
CONVERTER OPERATION
VIN
CAPACITIVE DAC
A SW1 B SW2
CONTROL LOGIC COMPARATOR
AGND
Figure 3. ADC Conversion Phase
ADC TRANSFER FUNCTION
The output coding of the AD7998/AD7997 is straight binary. The designed code transitions occur at successive integer LSB values (i.e., 1LSB, 2LSBs, etc.). The LSB size for the AD7998 is = REFIN/4096 and REFIN/1024 for the AD7997 . The ideal transfer characteristic for the AD7998/AD7997 is shown in Figure 4 below.
111...111 111...110
ADC CODE
111...000 011...111
AD7998 1 LSB = REFIN/4096 AD7997 1 LSB = REFIN/1024
000...010 000...001 000...000
AGND +1 LSB
+REFIN -1LSB
The AD7998/AD7997 are successive approximation analog-to -digital converters based around a capacitive DAC. Figures 2 and 3 show simplified schematics of the ADC during its acquisition and conversion phase respectively. Figure 2 shows the ADC during its acquisition phase. SW2 is closed and SW1 is in position A, the comparator is held in a balanced condition and the sampling capacitor acquires the signal on VIN.
CAPACITIVE DAC
ANALOG INPUT 0 V TO REFIN
Figure 4. AD7998/AD7997 Transfer Characteristic
TYPICAL CONNECTION DIAGRAM
A VIN SW1 B SW2
Figure 5 shows the typical connection diagram for the AD7998/AD7997. In Figure 5 the Address Select pin, AS, is tied to VDD, however AS can also be either tied to GND or left floating, allowing the user to select up to three AD7998/AD7997 devices on the same serial bus. An external reference must be applied to the AD7998/ AD7997. This reference can be in the range of 1.2 V to VDD. A precision reference like the REF 192 or ADR421 can be used to supply the Reference Voltage to the ADC. SDA and SCL form the two-wire I2C/SMBus compatible interface. External pull-up resisters are required for both SDA and SCL lines. The AD7998-0/AD7997-0 support Standard and Fast I2C Interface Modes. While the AD7998-1/AD7997-1 support Standard, Fast and Highspeed I2C Interface Modes. Therefore if operating the AD7998/AD7997 in either Standard or Fast Mode, up to five AD7998/AD7997 devices (3 x AD7998-0/AD7997-0 and 2 x AD7998-1/ AD7997-1 or 3 x AD7998-1/AD7997-1 and 2 x AD7980/AD7997-0) can be connected to the bus. When operating in Hs-Mode then up to three AD7998-1/AD7997-1 devices can be connected to the bus. Wake-up from power-down prior to a conversion is approximately 1s while conversion time is approximately 2s. The AD7998/AD7997 enters shutdown mode again after each conversion, this will be useful in applications where power consumption is of concern.
CONTROL LOGIC COMPARATOR
AGND
Figure 2. ADC Acquisition Phase
When the ADC starts a conversion, see Figure 3, SW2 will open and SW1 will move to position B causing the comparator to become unbalanced. The input is disconnected once the conversion begins. The Control Logic and the Capacitive DAC are used to add and subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition. When the comparator is rebalanced the conversion is complete. The Control Logic generates the ADC output code. Figure 4 shows the ADC transfer function. REV. PrB
-13-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
+5V SUPPLY 10F 0.1F RP VIN1 0V to REFIN INPUT VIN8 VDD SDA SCL ALERT CON VST REF 19X 0.1F REFIN AGND AS
SET TO REQUIRED ADDRESS TWO WIRE SERIAL INTERFACE
RP
RP
AD7998/ AD7997
C/P
Figure 5 AD7998/AD7997 Typical Connection Diagram
Analog Input
Figure 6 shows an equivalent circuit of the analog input sturcture of the AD7998/AD7997. The two diodes D1 and D2 provide ESD protection for the analog inputs. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 300mV. This will cause these diodes to become forward biased and start conducting current into the substrate. 10mA is the maximum current these diodes can conduct without causing irreversable damage to the part. The capacitor C1 in Figure 6 is typically about 4pF and can primarily be attributed to pin capacitance. The resistor R1 is a lumped component made up of the on resistance (RON) of a switch (track and hold switch) and also includes the RON of the input multiplexer. The total resistor is typically about 400. The capacitor C2 is the ADC sampling capacitor and has a capacitance of 30 pF typically. For ac applications, removing high frequency components from the analog input signal is recommended by use of an RC band-pass filter on the relevant analog input pin. In applications where harmonic distortion and signal to noise ratio are critical the analog input should be driven from a low impedance source. Large source impedances will significantly affect the ac performance of the ADC. This may necessitate the use of an input buffer amplifier. The choice of the op amp will be a function of the particular application. When no amplifier is used to drive the analog input the source impedance should be limited to low values. The
maximum source impedance will depend on the amount of total harmonic distortion (THD) that can be tolerated. The THD will increase as the source impedance increases and performance will degrade. Figure 7 shows a graph of the Total Harmonic Distortion vs. analog input signal frequency for different source impedances when using a supply voltage of 3V10% and 5V10% and sampling at a rate of xkSPS. Figure 8 shows a graph of the total harmonic distortion versus analog input signal frequency for various supply voltages while sampling at xkSPS .
TBD
Figure 7. THD vs. Analog Input Frequency for Various Source Impedance for VDD = 3V and 5V
VDD
D1 R1 VIN C1 4PF D2
C2 30 pF
TBD
CONVERSION PHASE - SWITCH OPEN TRACK PHASE - SWITCH CLOSED
Figure 6. Equivalent Analog Input Circuit
Figure 8. THD vs. Analog Input Frequency for Various Supply Voltages, Fs = xkSPS
-14-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
INTERNAL REGISTER STRUCTURE ADDRESS POINTER REGISTER
The AD7998/AD7997 contains seventeen internal registers, as shown in Figure 9, that are used to store conversion results, high and low conversion limits, and to configure and control the device. Sixteen are data registers and one is an address pointer register.
CONVERSION RESULT REGISTER ALERT STATUS REGISTER CONFIGURATION REGISTER CYCLE TIMER REGISTER DATALOW REGISTER CH1 DATAHIGH REGISTER CH1 HYSTERESIS REGISTER CH1 ADDRESS POINTER REGISTER DATALOW REGISTER CH2 DATAHIGH REGISTER CH2 HYSTERESIS REGISTER CH2 DATALOW REGISTER CH3 DATAHIGH REGISTER CH3 HYSTERESIS REGISTER CH3 DATALOW REGISTER CH4 DATAHIGH REGISTER CH4 HYSTERESIS REGISTER CH4
The Address Pointer register itself does not have, nor does it require, an address, as it is the register to which the first data byte of every Write operation is written automatically. The Address Pointer Register is an 8-bit register in which the four LSBs are used as pointer bits to store an address that points to one of the data registers of the AD7998/ AD7997, while the four MSBs are used as command bits when using Mode 2 (see Modes of Operation section). The first byte following each write address is the address of one of the data registers, which is stored in the Address Pointer Register, and selects the data register to which subsequent data bytes are written. Only the four LSBs of this register are used to select a data register. On Power up the Address Point register contains all 0's, pointing to the Conversion Result Register.
Table II. Address Pointer Register
MSB C4 C3 0 C2 0 C1 0 P3 P2 P1
LSB P0
D A T A
0
Register Select
Table III. AD7998/AD7997 Register Addresses
P3 0 0 0 0 0 0 0 0 1 1
SDA
P2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1
P1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1
P0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
Registers Conversion Result Register (Read) Alert Status Register (Read/Write) Configuration Register (Read/Write) Cycle Timer Register (Read/Write) DATALOW Reg CH1 (Read/Write) DATA HIGH Reg CH1 (Read/Write) Hysteresis Reg CH1 (Read/Write) DATALOW Reg CH2 (Read/Write) DATA HIGH Reg CH2 (Read/Write) Hysteresis Reg CH2 (Read/Write) DATALOW Reg CH3 (Read/Write) DATA HIGH Reg CH3 (Read/Write) Hysteresis Reg CH3 (Read/Write) DATALOW Reg CH4 (Read/Write) DATA HIGH Reg CH4 (Read/Write) Hysteresis Reg CH4 (Read/Write)
1 1 1
SERIAL BUS INTERFACE
SCL
Figure 9. AD7998/AD7997 Register Structure
1 1
Each data register has an address which is pointed to by the Address Pointer register when communicating with it. The Conversion Result Register is the only data register that is read only.
1
REV. PrB
-15-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
CONFIGURATION REGISTER
The Configuration Register is an 12-bit read/write register that is used to set the operating modes of the AD7998/ AD7997. The bit functions of all 12 bits of the Configuration Register are outlined in Table IV.
Table IV.
Configuration Register Bit Function Description
D15 DONTC 0*
D14 DONTC 0*
D13 DONTC 0*
D12
D11
D10 CH7 0*
D9 CH6 0*
D8 CH5 0*
D O N T C CH8 0* 0*
D7 CH4 0*
D6 CH3 0*
D5 CH2 0*
D4 CH1 0*
D3 FLTR 1*
D2
D1
D0 ALERT/BUSY POLARITY 0*
ALERT EN B U S Y / A L E R T 1* 0*
*Default settings at Power-up
Bit D11-D4
Mnemonic CH8-CH1
Comment These eight channel address bits select the analog input channel(s) to be converted on. A 1 in any of bits D11 to D4 selects a channel for conversion. If more than one channel bit is set to 1 then the AD7998/AD7997 will sequence through the selected channels, starting with the lowest channel. All unused channels should be set to zero. The value written to this bit of the Control Register determines whether the filtering on SDA and SCL is enabled or to be bypassed. If this bit is a 1 then the the filtering is enabled, if it is a 0, then the filtering is bypassed. The hardware ALERT function is enabled if this bit is set to 1 and disabled if set to 0. This bit is used in conjunction with the BUSY/ALERT bit to determine if the ALERT/BUSY pin will act as an ALERT or a BUSY output. (See Table VI.) This bit is used in conjunction with the ALERT EN bit to determine if the ALERT/ BUSY output, pin 17, will act as an ALERT or BUSY output (see TABLE V1), and if pin 17 is configured as an ALERT output pin, if it is to be reset. This bit determines the active polarity of the ALERT/BUSY pin regardless of whether it is configured as an ALERT or BUSY output. It is active low if this bit is set to 0, and it is active high if set to 1.
D3
FLTR
D2
ALERT EN
D1
BUSY/ALERT
D0
BUSY/ALERT POLARITY
-16-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
Table V. Channel Selection
D11 D10 D9 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0
D8 0 0 0 0 1 0 0 0
D7 0 0 0 1 0 0 0 0
D6 0 0 1 0 0 0 0 0
D5 0 1 0 0 0 0 0 0
D4 1 0 0 0 0 0 0 0
Selected Analog Input Channel Convert Convert Convert Convert Convert Convert Convert Convert on on on on on on on on Channel Channel Channel Channel Channel Channel Channel Channel 1 2 3 4 5 6 7 8 (VIN1) (VIN2) (VIN3) (VIN4) (VIN5) (VIN5) (VIN6) (VIN7)
If more than one Channel is selected then the AD7998/AD7997 will start converting on the selected sequence of channels starting with the lowest channel in the sequence.
Table VIII. Table VI. ALERT/BUSY Function Channel Identifier Bits from the Conversion Result Register
ID2
D2 0 0 1 1
D1 0 1 0 1
ALERT/BUSY Pin Configuration Pin does not provide any interrupt signal. Pin configured as a BUSY output. Pin configured as an ALERT output. Resets ALERT output pin, Alert_Flag bit in Conversion Result Reg, and entire Alert Status Reg ( if any active).
Alert_Flag1 CH 0/1 0/1 0/1 0/1 0/1 0/1 0 0 0 0 1 1 1 1
CH 0 0 1 1 0 0 1 1
ID1
CH 0 1 0 1 0 1 0 1
ID0
Channel# Result Channel 1(V IN1) Channel 2(V IN2) Channel 3(V IN3) Channel 4(V IN4) Channel 5(V IN5) Channel 6(V IN6) Channel 7(V IN7) Channel 8(V IN8)
CONVERSION RESULT REGISTER
0/1 0/1
The Conversion Result Register is a 16-bit read-only register which stores the conversion result from the ADC in Straight Binary format. A Two byte read is necessary to read data from this register. Table VIIa shows the contents of the first byte to be read while Table VIIb show the contents of the second byte to be read from AD7998/ AD7997.
Table VIIa. Conversion Value Register (First Read)
Note:1 A 1 in the Alert_Flag bit indicates a violation of one of the limit Registers has occured on the channel indicated by CH ID2 , CH ID1 , CH ID0 . A 0 in the Alert_Flag bit indicates that no violation of the limit Register has occured on the channel indicated by CH ID2 , CH ID1, CH ID0 .
D15
D14
ID2
D13 CH
ID1
D12 CH
ID0
D11
D10
D9 B9
D8 B8
Alert_FlagCH
M S B B10
Table VIIb. Conversion Value Register (Second Read)
D7 B7
D6 B6
D5 B5
D4 B4
D3 B3
D2 B2
D1 B1
D0 B0
The AD7998/AD7997 conversion result consists of an Alert_Flag bit, three Channel Identifier bits and the 12-/ 10- bit data result. For the AD7997 the 2 LSBs (D1 and D0) of the second read will contain two zeros. The Alert_Flag bit indicates whether the conversion result being read has violated the limit registers associated with it. This is followed by three Channel Indentifier bits indicating which channel the conversion result corresponds to. The 12-/10-bit conversion result then follows MSB first.
REV. PrB
-17-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
LIMIT REGISTERS
The AD7998/AD7997 has four pairs of limit registers, each pair stores high and low conversion limits for the first four analog input channels. Each pair of limit registers has an associated hysteresis register. These limit registers and hysteresis registers are associated with CH1 to CH4. All twelve registers are 16-bits wide, only the 12 LSBs of the Registers are used for the AD7998/ AD7997.For the AD7997 the 2 LSBs D1 and D0 should contain 0s. On power-up, the contents of the DATAHIGH register for each channel will be fullscale, while the contents of the DATALOW registers will be zeroscale by default. The Limit Registers can be used to monitor the conversion results on each on the Analog input channels. The AD7998/AD7997 will signal an Alert (in either hardware or software or both depending on configuration) if the result moves outside the upper or lower limit set by the limit Registers. There are no limit registers or hysteresis registers associated with CH5 to CH8.
DATA HIGH REGISTER CH1/CH2/CH3/CH4
the 12-bit Hysteresis register associated with that channel. The ALERT output pin can also be reset by writing to bit D2,D1 in the Configuration Register. For the AD7997 D1 to D0 of the DATALOW Register should contain 0's.
Table IXa. DATALOW Register (First Read/Write)
D15
D14
D13 D12 0 0
D11 B11
D10 B10
D9 B9
D8 B8
Alert_Flag 0
Table IXb.
DATALOW Register (Second Read/Write)
D7 B7
D6 B6
D5 B5
D4 B4
D3 B3
D2 B2
D1 B1
D0 B0
HYSTERESIS REGISTER (CH1/CH2/CH3/CH4)
The DATAHIGH Registers for CH 1 to CH 4 are 16-bit read/write Registers, only the 12 LSBs of each Register are used. The Registers store the upper limit that will activate the ALERT output and/or the Alert_Flag bit in the Conversion Result Register. If the value in the Conversion Result Register is greater than the value in the DATAHIGH Register, then the Alert_Flag bit is set to 1 and the ALERT output pin is activated (the latter is true if ALERT is enabled in the Configuration Register). When the conversion result returns to a value at least N LSBs below the DATAHIGH Register value the ALERT output pin and Alert_Flag bit will be reset. The value of N is taken from the 12-bit Hysteresis register associated with that channel. The ALERT pin can also be reset by writing to bits D2,D1 in the Configuration Register. For the AD7997 D1 and D0 of the DATAHIGH Register should contain 0's.
Table VIIIa. DATAHIGH Register (First Read/Write)
Each Hysteresis Register is a 16-bit read/write register, of which only the 12 LSBs of the register are used. The Hysteresis register stores the hysteresis value, N when using the limit registers. Each pair of Limit registers has a dedicated hysteresis register. The hysteresis value determines the reset point for the ALERT pin/Alert_Flag if a violation of the limits has occurred. If hysteresis value of say 8 LSBs is required on the upper and lower limits of channel 1 then the 12 bit word, 0000 0000 0000 1000, should be written to the Hysteresis Register of CH1, the address of which is shown in Table III. On power up, the Hysteresis Registers will contain a value of TBD LSBs. If a different hysteresis value is required then that value must be written to the Hysteresis Register for the channel in question. For the AD7997 D1 and D0 of the Hysteresis Register should contain 0's.
Table Xa. Hysteresis Register (First Read/Write)
D15
D14
D13 D12 0 0
D11 B11
D10 B10
D9 B9
D8 B8
Alert_Flag 0 D15 D14 D13 D12 0 0 D11 B11 D10 B10 D9 B9 D8 B8 D7 B7
Table VIIIb. DATAHIGH Register (Second Read/Write) Table Xb.
Hysteresis Register (Second Read/Write)
Alert_Flag 0
D6 B6
D5 B5
D4 B4
D3 B3
D2 B2
D1 B1
D0 B0
D7 B7
D6 B6
D5 B5
D4 B4
D3 B3
D2 B2
D1 B1
D0 B0
DATALOW REGISTER CH1/CH2/CH3/CH4
The DATALOW Register for each channel is a 16-bit read/ write register, only the 12 LSB of each registers are used. The Register stores the lower limit that will activate the ALERT output and/or the Alert_Flag bit in the conversion result register. Therefore, if the value in the Conversion Result Register is less than the value in the DATALOW Register, then the Alert_Flag bit is set to 1 and the ALERT pin is activated (the latter is true if ALERT is enabled in the Configuration Register). When the Conversion result returns to a value at least N LSBs above the DATALOW Register value the ALERT ouput pin and Alert_Flag bit will be reset. The value of N is taken from
Using the Limit Registers to Store Min/Max Conversion Results for CH1 to CH4 If fullscale, i.e. all 1s, are written to the Hysteresis register for a particular channel then the DATAHIGH and DATALOW Registers for that channel will no longer act as Limit registers as previously described, but instead they will act as storage registers for the maximum and minimum conversion results returned from conversions on a channel over any given period of time. This function is useful in applications where the widest span of actual conversion results is required rather than using the ALERT to signal an intervention is necessary, e.g. monitoring temperature extremes during refrigerated goods transportation. It must be noted that on power-up, the contents of the DATAHIGH register for each channel will be fullscale, while the contents of the DATALOW registers will be
-18-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
zeroscale by default so minimum and maximum conversion values being stored in this way will be lost if power is removed or cycled. When using the limit registers to store the min and max conversion results, the Alert_Flag bit, D15, is used to indicate that an alert has happened on another one of the Input channels. If the Alert_Flag bit is set to 1, it will be reset when the Conversion result returns to a value at least N LSBs above the DATALOW Register value or below the DATALOW Register value or if bits D2 and D1 of the Configuration Register are set to 1. The Alert_Flag bit in the limit registers is useful if the user is not reading from the conversion result register when reading the min and max conversion results from the limit registers.
ALERT STATUS REGISTER (CH1 to CH4) Table XIb. Alert Status Register Bit Function Description
Bit Mnemonic Comment D 0 CH1 LO D 1 CH1 HI D 2 CH2 LO D 3 CH2 HI D 4 CH3 LO Violation of DATALOW limit on Channel 1 if this bit set to 1, no violation if 0. Violation of DATAHIGH limit on Chan nel 1 if this bit set to 1, no violation if 0. Violation of DATALOW limit on Channel 2 if this bit set to 1, no violation if 0. Violation of DATAHIGH limit on Chan nel 2 if this bit set to 1, no violation if 0. Violation of DATALOW limit on Channel 3 if this bit set to 1, no violation if 0. Violation of DATAHIGH limit on Chan nel 3 if this bit set to 1, no violation if 0. Violation of DATALOW limit on Channel 4 if this bit set to 1, no violation if 0. Violation of DATAHIGH limit on Chan nel 4 if this bit set to 1, no violation if 0.
The Alert Status Register is a 8-bit read/write register, which provides information on an Alert event. If a conversion results in activating the ALERT pin or the Alert_Flag bit in the Conversion Result Register, as described in the Limit Registers section, then the Alert Status Register may be read to gain further information. It contains 2 status bits per channel, one corresponding to the DATAHIGH limit and the other to the DATALOW limit. Whichever bit has a status of 1 will show where the violation occured, i.e. on which channel and whether the violation occured on the upper or lower limit. If a second alert event occurs on the other channel between receiving the first alert and interrogating the Alert Status register then the corresponding bit for that Alert event will be set also. The Alert Status Register contains information for CH1 to CH4 only as these are the only channels with associated limit registers. The entire contents of the Alert Status register may be cleared by writing 1,1, to bits D2 and D1 in the Configuration register as shown in Table VI. This may also be achieved by `writing' all 1's to the Alert Status Register itself. This means that if the Alert Status Register is addressed for a write operation which is all 1's, then the contents of the Alert Status Register will then be cleared or resest to all 0's. Alternatively, the individual active Alert bit(s) may be reset within the Alert Status Register by performing a write of `1' to the bit(s) alone. The advantage of this is that once an Alert event has been serviced, that particular bit can be reset, e.g. CH1LO, without clearing the entire contents of the Alert Status Register, thus preserving the status of any additional Alert, e.g. CH2HI, which may have occured while servicing the first. If it is not necessary to clear an Alert directly after servicing then obviously the Alert Status register may be read again immediately to look for any new Alerts, bearing in mind that the one just serviced will still be active.
Table XIa. Alert Status Register
D 5 CH3 HI D 6 CH4 LO D 7 CH4 HI
CYCLE TIMER REGISTER
The Cycle Timer Register is a 8-bit read/write register, which stores the conversion interval value for the Automatic Cycle mode of the AD7998/AD7997, see Modes of Operation section. The five MSBs of the Cycle Timer Register are unused and should contain 0's at all times. On power up, the Cycle Timer Register will contain all 0s, thus disabling the Automatic Cycle operation of the AD7998/AD7997. To enable the Automatic Cycle Mode the user must write to the Cycle Timer Register, selecting the required conversion interval. Table XIIa shows the structure of the Cycle Timer register while Table XIIb shows how the bits in this register are decoded to provide various automatic sampling intervals.
Table XIIa. Cycle Timer Register
D7 0
D6 0
D5 0
D4 0
D3 0
D2 B2
D1 B1
D0 B0
Table XIIb.
Cycle Timer Intervals
D2 D1 D0 0 0 0 0 1 1 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 1 0 1
Conversion Interval Mode not selected 64 s 128 s 256 s 512 s 1.024 ms 2.048 ms 4.096 ms
D7
D6
D5
D4
D3
D2
D1
D0
CH4HI CH4 LO CH3HI CH3 LO CH2HI CH2 LO CH1HI CH1 LO
REV. PrB
-19-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
SERIAL INTERFACE Control of the AD7998/AD7997 is carried out via the I2C-compatible serial bus. The AD7998/AD7997 is connected to this bus as a slave device, under the control of a master device, e.g. the processor.
SERIAL BUS ADDRESS
high transition when the clock is high may be interpreted as a STOP signal. 3. When all data bytes have been read or written, stop conditions are established. In WRITE mode, the master will pull the data line high during the 10th clock pulse to assert a STOP condition. In READ mode, the master device will pull the data line high during the low period before the 9th clock pulse. This is known as No Acknowledge. The master will then take the data line low during the low period before the 10th clock pulse, then high during the 10th clock pulse to assert a STOP condition. Any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation, because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation.
WRITING TO THE AD7998/AD7997
Like all I2 C-compatible devices, the AD7998/AD7997 has a 7-bit serial address. The three MSBs of this address for the AD7998/AD7997 are set to 010. The AD7998/ AD7997 comes in two versions, the AD7998-0/AD7997-0 and AD7998-1AD7997-1. The two versions have three different I2C addresses available which are selected by either tying the Address Select pin, AS, to GND, to VDD or letting the pin float (see Table I). By giving different addresses for the two versions, up to five AD7998/ AD7997 devices can be connected to a single serial bus, or the addresses can be set to avoid conflicts with other devices on the bus. See I2C Address Selection table. The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, defined as a high to low transition on the serial data line SDA whilst the serial clock line, SCL, remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next 8 bits, consisting of a 7-bit address (MSB first) plus a R/W bit, which determines the direction of the data transfer, i.e. whether data will be written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowledge Bit. All other devices on the bus now remain idle whilst the selected device waits for data to be read from or written to it. If the R/W bit is a 0 then the master will write to the slave device. If the R/W bit is a 1 the master will read from the slave device. 2. Data is sent over the serial bus in sequences of 9 clock pulses, 8 bits of data followed by an Acknowledge Bit from the receiver of data. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, as a low to
Depending on the register being written to, there are two different writes for the AD7998/AD7997.
Writing to the Address Pointer Register for a Subsequent Read
In order to read from a particular register, the Address Pointer register must first contain the address of that register. If it does not, the correct address must be written to the Address pointer register by performing a single-byte write operation, as shown in Figure 10. The write operation consists of the serial bus address followed by the address pointer byte. No data is written to any of the data registers. A read operation maybe subsequently performed to read the register of interest.
Writing a Single Byte of Data to the Configuration Register or Cycle Register
The Configuration Register and Cycle Register are both 8-bit registers, so only one byte of data can be written to each. Writing a single byte of data to one of these registers consists of the serial bus write address, the chosen data register address written to the Address Pointer Register, followed by the data byte written to the selected data register. This is illustrated in Figure 11.
Writing two Bytes of Data to a Limit Register
Each of the four Limit Registers are 12-bit registers, so two bytes of data are required to write a value to any one of them. Writing two bytes of data to one of these registers consists of the serial bus write address, the chosen Limit Register address written to the Address Pointer Register, followed by two data bytes written to the selected data register. This is illustrated in Figure 12.
9 1 9
1 SCL
SDA START BY MASTER
0
1
0
A3
A2
A1
A0
R/9 ACK. BY AD7998/7
C4
C3
C2
C1
P3
P2
P1
P0 ACK. BY AD7998/7 STOP BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
Figure 10. Writing to the Address Pointer Register to select a register for a subsequent Read operation
-20-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
A3
A2
A1
A0
R/9 ACK. BY AD7998/7
C4
C3
C2
C1
P3
P2
P1
P0 ACK. BY AD7998/7
FRAME 1 SERIAL BUS ADDRESS BYTE 9 SCL (CONTINUED) 1
FRAME 2 ADDRESS POINTER REGISTER BYTE 9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY AD7998/7 STOP BY MASTER
FRAME 3 DATA BYTE
Figure 11. Single Byte Write Sequence
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
A3
A2
A1
A0
R/9 ACK. BY AD7998/7
C4
C3
C2
C1
P3
P2
P1
P0 ACK. BY AD7998/7
FRAME 1 SERIAL BUS ADDRESS BYTE 9 SCL (CONTINUED) 1 9 1
FRAME 2 ADDRESS POINTER REGISTER BYTE 9
SDA (CONTINUED)
0
0
0
0
D11
D10
D9
D8 ACK. BY AD7998/7
D7
D6 STOP BY MASTER
D5
D4
D3
D2
D1/0
D0/0 ACK. BY AD7998/7 STOP BY MASTER
MOST SIGNIFICANT DATA BYTE
LEAST SIGNIFICANT DATA BYTE
Figure 12. Two Byte Write Sequence
READING DATA FROM THE AD7998/AD7997
Reading data from the AD7998/AD7997 is a one or two byte operation. Reading back the contents of the Alert Status Register or the Cycle Timer Register is a single byte read operation as shown in Figure 13. This assumes the particular register address has previously been set up by a single byte write operation to the Address Pointer Register, Figure 10. Once the register address has been set up, any number of reads can subsequently be performed from that particular register without having to write to the Address Pointer Register again. If a read from a different register is required, then the relevant register address will have to be written to the Address Pointer Register and again any number of reads from this register may then be performed.
Reading data from the Configuration Register, Conversion Result Register, DATAHIGH Registers, DATALOW Registers or Hysteresis Registers is a two byte operation as shown in Figure 14. The same rules apply for a two byte read as a single byte read.
REV. PrB
-21-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
A3
A2
A1
A0
R/9 ACK. BY AD7998/7
D7
D6
D5
D4
D3
D2
D1
D0 NO ACK. BY MASTER STOP BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 SINGLE DATA BYTE FROM AD7998/7
Figure 13. Reading a single byte of data from a selected register
1 SCL 9 1 9
SDA START BY MASTER
0
1
0
A3
A2
A1
A0
R/9
Alert_ Flag ACK. BY AD7998/7 CH ID2 CH ID1 CH ID0
D11
D10
D9
D8 ACK. BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL (CONTINUED)
FRAME 2 MOST SIGNIFICANT DATA BYTE FROM AD7998/7
9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1/0
D0/0 NO ACK. BY MASTER STOP BY MASTER
FRAME 3 LEAST SIGNIFICANT DATA BYTE FROM AD7998/7
Figure 14. Reading two bytes of data from the Conversion Result Register
ALERT/BUSY PIN
The ALERT/BUSY may be configured as an Alert output or Busy ouput as shown in Table VI.
SMBus ALERT
device will win communication rights via standard I2C arbitration during the slave address transfer. The ALERT output becomes active when the value in the Conversion Result Register exceeds the value in the DATAHIGH Register or falls below the value in the DATALOW Register . It is reset when a write operation to the Configuration register sets D1 to a 1, or when the conversion result returns N LSBs below or above the value stored in the DATA HIGH Register or DATALOW Register respectively. N is the value in the Hysteresis register. (See Limit Registers section) The ALERT output requires an external pull-up resistor. This can be connected to a voltage different from VDD provided the maximum voltage rating of the ALERT output pin is not exceeded. The value of the pull-up resistor depends on the application, but should be as large as possible to avoid excessive sink currents at the ALERT output.
The AD7998/AD7997 ALERT output is an SMBus interrupt line for devices that want to trade their ability to master for an extra pin. The AD7998/AD7997 is a slave only device and uses the SMBus ALERT to signal the host device that it wants to talk. The SMBus ALERT on the AD7998/AD7997 is used as an out of conversion range indicator (a limit violation indicator). The ALERT pin has an open-drain configuration which allows the ALERT outputs of several AD7998/AD7997 devices to be wired-AND together when the ALERT pin is active low. D0 of the Configuration Register is used to set the active polarity of the ALERT output. The powerup default is active low. The ALERT function can be disabled or enabled by setting D2 of the Configuration Register to 1 or 0 respectively. The host device can process the ALERT interrupt and simultaneously access all SMBus ALERT devices through the alert response address. Only the device which pulled the ALERT low will acknowledge the ARA (Alert Response Address). If more than one device pulls the ALERT pin low, the highest priority (lowest address)
-22-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
Placing the AD7998-1/AD7997-1 into High-speed Mode. Hs-Mode communication commences after the master addresses all devices connected to the bus with the Master code, 00001XXX, to indicate that a High-Speed Mode transfer is to begin. No device connected to the bus is allowed to Acknowledge the High-Speed Master code, therefore the code is followed by a not-Acknowledge, FigFAST MODE 1 SCL 9 1
ure 15. The master must then issue a repeated start followed by the device Address with a R/W bit. The selected device will then acknowledge its address. All devices continue to operate in Hs-Mode until such a time as the master issues a STOP condition. When the STOP condition is issued the devices all return to F/S Mode.
HIGH-SPEED MODE 9
SDA START BY MASTER
0
0
0
0
1
X
X
X NACK. Sr
0
1
0
A3
A2
A1
A0 ACK. BY AD7998/7
HS-MODE MASTER CODE
SERIAL BUS ADDRESS BYTE
Figure 15. Placing the part into Hs Mode
MODES OF OPERATION
When supplies are first applied to the AD7998/AD7997, the ADC powers up in sleep mode and will normally remain in this shutdown state while not converting. There are three different methods of initiating a conversion on the AD7998/AD7997. Mode 1 - Using CONVST Pin. A conversion can be initiated on the AD7998/AD7997 by pulsing the CONVST signal. The conversion clock for the part is internally generated so no external clock is required, except when reading from, or writing to the serial port. On the rising edge of CONVST the AD7998/ AD7997 will begin to power up, see point A on Figure 16. The power up time from shutdown mode for the AD7998/AD7997 is approximately 1 us, the CONVST signal must remain high for 1 s for the part to power up fully. Then CONVST can be brought low after this time. The falling edge of the CONVST signal places the track and hold into hold mode and a conversion is also initiated at this point, see point B Figure 16. When the conversion
is complete, approximately 2 us later, the part will return to shutdown (see point C Figure 16) and remain so until the next rising edge of CONVST. The master can then read address the ADC to obtain the conversion result. The address point register must be pointing to the conversion result register in order to read back the conversion result. If the CONVST pulse does not remain high for more than 1 s, then the falling edge of CONVST will still initiate a conversion but the result will be invalid as the AD7998/AD7997 will not be fully powered up when the conversion takes place. The CONVST pin should not be pulsed when reading from or writing to the serial port. The Cycle Timer Register and bits C4 - C1 in the Address Pointer Register should contain all 0's to operate the AD7998/AD7997 in this mode. The CONVST pin should be tied low for all other Modes of operation. To select an Analog Input Channel for conversion in this mode, the user must write to the Configuration Register and select the corresponding channel for conversion. To set up a sequence of channels to be converted on with each CONVST pulse, set the corresponding channel bits in the Configuration register, see Table V.
A
B
C
tPOWER-UP
CONVST
tCONVERT
1
91
9
9
SCL SDA
S 7-BIT ADDRESS R A FIRST DATA BYTE (MSBs) A SECOND DATA BYTE (LSBs) ) P
Figure 16. Mode 1 Operation
REV. PrB
-23-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
Mode 2 This mode allows a conversion to be automatically initiated anytime a read operation occurs. In order to use this mode the command bits C4 - C1 in the Address Pointer Byte shown in Table II must be programmed. To select a single Analog input for conversion in this mode, then the user must set bits C4-C1of the Address Pointer Byte to indicate which channel to convert on, see Table XIII. When all four command bits are 0 then this mode is not in use. A sequence can also be set up for this mode. With the Command bits of the Address Pointer Byte set to 0111, the ADC will know to look in the configuration register for the Sequence of channel to be converted. The ADC will start converting on the lowest channel in the sequence and then the next lowest until all the channels in the sequence have been converted on. The ADC will stop converting the sequence when it recieves a STOP bit. Therefore to select an individual channel for conversion set the command bits of the Address Pointer Byte as shown in Taqble XIII. To select a sequence of channels for conversion select the channel to be included in the sequence by setting the channel bits in the Configuration Register then set the command bits in the Address Pointer Byte to 0111. Figure 13 illustrates a two byte read operation from the Conversion Result Register. This operation would normally be preceded by a write to the Address Pointer Register so that the following read will access the desired register, in this case the Conversion Result Register Figure 10. When the contents of the Address Pointer Register are being loaded, if the command bits C4 to C1 are set then the AD7998/AD7997 will begin to power up and convert upon the selected channel(s), power-up will begin on the fourth SCL rising edge of the Address Point Byte, see point A Figure 17. Table XIII shows the channel selection in this mode via the command bits, C4 to C1 in the Address Pointer Register. The wake-up and conversion time together should take approximately 3s, and this process begins when the last Command bit, C1 has been clocked in midway through the write to the Address Pointer Register. Following this, the AD7998/AD7997 must be addressed again to tell it that a read operation is required. The read then takes place from the Conversion Result register. This read will access the result from the conversion selected via the command bits. If the Command bits C4 to C1 were set to 0111, and bits D4 and D5 were set in the Configuration Register then a four byte read would be necessary. The first read accesses the data from the conversion on VIN1. While this read takes place, a conversion occurs on VIN2. The second read will access this data from VIN2. Figure 18 illustrates how this mode operates, the user would firstly have written to the Configuration Register to select the sequence of channels to be converted on before read Addressing the part with the command bits set. When operating the AD7998-1/AD7997-1 in Mode2 with Hs-Mode, 3.4 MHz SCL, the conversion may not be complete before the master tries to read the conversion result, if this is the case the AD7998-1/AD7997-1 will hold the SCL line low after the read address during the ACK clock, until the conversion is complete. When the conversion is complete the AD7998-1/AD7997-1 will release the SCL line and the master can then read the conversion result.
Table XIII Address Pointer Byte
C4 0 1 1 1 1 1 1 1 1 0
C3 0 0 0 0 0 1 1 1 1 1
C2 0 0 0 1 1 0 0 1 1 1
C1 0 0 1 0 1 0 1 0 1 1
P3 0 0 0 0 0 0 0 0 0 0
P2 0 0 0 0 0 0 0 0 0 0
P1 0 0 0 0 0 0 0 0 0 0
P0 0 0 0 0 0 0 0 0 0 0
Analog Input Channel Mode 2 No Selected Mode 2 Convert on VIN1 Mode 2 Convert on VIN2 Mode 2 Convert on VIN3 Mode 2 Convert on VIN4 Mode 2 Convert on VIN5 Mode 2 Convert on VIN6 Mode 2 Convert on VIN7 Mode 2 Convert on VIN8 Mode 2 Convert on Sequence of Channels selected in the Configuration Register, bits D11 to D4.
With the pointer bits, P3-P0, set to all 0's then the next read will access the results of the conversion Result Register.
-24-
REV. PrB
PRELIMINARYTECHNICAL DATA AD7998/AD7997
1 8 91 A 9
SCL SDA
S 7-BIT ADDRESS W A COMMAND/ADDRESS POINT BYTE A ACK BY AD7998/7 ACK BY AD7998/7
1
91
9
9
SCL SDA
Sr 7-BIT ADDRESS R A ACK BY MASTER FIRST DATA BYTE (MSBs) A SECOND DATA BYTE (LSBs) ) ACK BY MASTER
Sr/ P
NACK BY MASTER
Figure 17. Mode 2 Operation
A
1
8
91
9
SCL SDA
S
7-BIT ADDRESS
W
A COMMAND/ADDRESS POINT BYTE A ACK BY AD7998/7 ACK BY AD7998/7
1
91
9
9
9
9
SCL SDA
Sr
7-BIT ADDRESS
R
A ACK BY MASTER
FIRST DATA BYTE (MSBs)
A
SECOND DATA BYTE (LSBs)
A ACK BY MASTER
FIRST DATA BYTE (MSBs)
A
SECOND DATA BYTE (LSBs)
A/)
ACK BY MASTER
RESULT FROM CH1
ACK BY MASTER
RESULT FROM CH2
Figure 18. Mode 2 Sequence Operation
Mode 3 - Automatic Cycle Mode An automatic conversion cycle can be selected and enabled by writing a value to the Cycle Timer Register. A conversion cycle interval can be set up on the AD7998/AD7997 by programming the relevant bits in the 8-bit Cycle Timer Register as decoded in Table XIIb. Only the 3 LSBs are used, the 5 MSBs should contain 0's. When the Cycle Timer register is programmed with any configuration other than all 0's, a conversion will take place every X ms, the cycle interval will depend on the configuration of these bits in the Cycle Timer Register. There are 7 different cycle time intervals to choose from as shown in Table XIIb. Once the conversion has taken place the part powers down again until the next conversion occurs. To exit this mode of operation the user must program the Cycle Timer Register to contain all 0's. For cycle interval options see Table XIIb Cycle Timer Intervals. To select a channel(s) for operation in the cycle mode set the corresponding channel bit(s), D11 to D4, of the Configuration Register. If more than one channel bit is set in the Configuration register the ADC will automatically cycle through the Channel sequence, starting with the lowest channel and working its way up through the sequence. Once the sequence is complete the ADC will start converting on the lowest channel again, continuing to loop through the sequence until the Cycle timer register contents are set to all 0's. This mode is useful for monitoring signals, e.g. battery voltage, temperature etc, alerting only when the limits are violated.
REV. PrB
-25-
PRELIMINARYTECHNICAL DATA AD7998/AD7997
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
20-Lead TSSOP (RU-20)
0.260 (6.60) 0.252 (6.40)
20
11
0.177 (4.50) 0.169 (4.30)
1
10
0.006 (0.15) 0.002 (0.05)
PIN 1 0.0433 (1.10) MAX 0.0079 (0.20) 0.0035 (0.090)
0.256 (6.50) 0.246 (6.25)
SEATING PLANE
0.0256 (0.65) BSC
0.0118 (0.30) 0.0075 (0.19)
8o 0o
0.028 (0.70) 0.020 (0.50)
-26-
REV. PrB

▲Up To Search▲

Price & Availability of AD7998

	To Download AD7998 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .