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LTC1427-50 Micropower, 10-Bit Current Output DAC with SMBus Serial Interface
FEATURES
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DESCRIPTION
The LTC(R)1427-50 is a micropower, 10-Bit current output DAC with an output range of 0A to 50A. The DAC output is guaranteed monotonic and DNL is less than 0.9LSB under all operating conditions. Full-scale accuracy is 2.5% over the commercial temperature range. The LTC1427-50 operates with power supply voltages from 2.7V to 5.5V and the DAC current source output can be biased from (VCC - 1.3V) to - 15V. The LTC1427-50 communicates with external circuitry by using the SMBus serial interface. It acts as an SMBus slave device using one of four selectable SMBus addresses set by the two address pins AD0 and AD1 . On power-up, the DAC output assumes midrange or zero scale, depending on the logic state of the two address pins. The LTC1427-50 can be shut down through the SHDN pin or by setting the SHDN bit = 1 in the SMBus command byte. Digital data for the DAC output is retained internally and the supply current drops to 10A typically when in shutdown. The LTC1427-50 is available in an 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Precision 50A, 1.5% Initial Full-Scale Output Current, 2.5% Over Temperature Wide Output Voltage DC Compliance: - 15V to (VCC - 1.3V) Wide Supply Range: 2.7V VCC 5.5V Supply Current in Shutdown: 10A Typ Low Supply Current: 115A Typ Available in 8-Pin SO SMBus Serial Interface Four Selectable SMBus Addresses DAC Powers Up at Zero or Midscale DAC Contents Are Retained in Shutdown
APPLICATIONS
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LCD Contrast and Backlight Brightness Control Power Supply Voltage Adjustment Battery Charger Voltage/Current Adjustment GaAs FET Bias Adjustment Trimmer Pot Elimination
TYPICAL APPLICATION
Digitally Controlled LCD Bias Generator
L1 D1 VOUT* 6 VIN 2 TO 4 CELLS SHDN 1F 3 LT1317 SHDN GND 4 FB VC 1 4700pF 100k 5 SW 2 R2 12.1k 1% C1 1F R1 226k 1%
LTC1427-50 1 2 3 4 SHDN AD1 AD0 GND VCC IOUT SCL SDA 8 7 6 5 PU (e.g., 8051) P1.2 P1.1 P1.0
L1 = 10 H SUMIDA CD43 MURATA-ERIE LQH3C OR COILCRAFT DO1608 D1 =MBR0530
*VOUT = 12.7V TO 24V IN 11mV STEPS 15mA (2 CELLS) 35mA ( 3 CELLS)
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VCC 3.3V
1427 TA02
1
LTC1427-50
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW SHDN 1 AD1 2 AD0 3 GND 4 8 7 6 5 VCC IOUT SCL SDA
Total Supply Voltage (VCC) ........................................ 7V Input Voltage (All Inputs)............. - 0.3V to (VCC + 0.3V) DAC Output Voltage ...................... - 15V to (VCC + 0.3V) DAC Output Short-Circuit Duration .................. Indefinite Operating Ambient Temperature Range ....... 0C to 70C Junction Temperature .......................................... 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec.)................. 300C
ORDER PART NUMBER LTC1427CS8-50 S8 PART MARKING 14275
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 190C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL VCC ICC PARAMETER Supply Voltage Supply Current DAC Resolution IFS IZS DNL DAC Full-Scale Current DAC Zero-Scale Current DAC Differential Nonlinearity Supply Voltage Rejection Output Voltage Rejection IIN VIH Logic Input Current High Level Input Voltage CONDITIONS
TA = operating temperature range unless otherwise specified.
MIN
q
TYP 115 10 10
MAX 5.5 225 25 50.75 51.25 200 0.9 8 5 1
UNITS V A A Bits A A nA LSB LSB LSB A V V V
2.7
VSHDN = VSCL = VSDA = VCC = 3.3V VSHDN = 0V VCC = 3.3V, V(IOUT) = 0V
q q q q
49.25 48.75
50 50 0.1 0.15
VCC = 3.3V, V(IOUT) = 0V VCC = 3.3V, Monotonicity Guaranteed, V(IOUT) = 0V VCC = 2.7V to 5.5V, V(IOUT) = 0V VCC = 3.3V, Full-Scale Current, - 15V V(IOUT) 2V 0V VIN VCC AD0, AD1 SHDN SCL, SDA SHDN, AD0, AD1 SCL, SDA IOUT = 3mA, SDA Only
q q q q q q q q q q q
VCC - 0.3 2.4 1.4 0.8 0.6 0.4
VIL VOL
Low Level Input Voltage Low Level Output Voltage
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WW
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V V V
LTC1427-50
RECO
SYMBOL fSMB tBUF tHD:STA tSU:STA tSU:STO tHD:DAT tSU:DAT tLOW tHIGH tf tr
E DED OPERATI G CO DITIO S
CONDITIONS
q q q q q q q q q q q
VCC = 3.3V, TA = operating temperature range unless otherwise specified.
PARAMETER SMB Operating Frequency Bus Free Time Between Stop and Start Condition Hold Time After (Repeated) Start Condition Repeated Start Condition Setup Time Stop Condition Setup Time Data Hold Time Data Setup Time Clock Low Period Clock High Period Clock/Data Fall Time Clock/Data Rise Time MIN 10 4.7 4.0 4.7 4.0 300 250 4.7 4.0 50 300 1000 TYP MAX 100 UNITS kHz s s s s ns ns s s ns ns SMBus Timing (Notes 2, 3)
The q denotes specifications that apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those beyond which the life of the device may be impaired.
Note 2: All values are referenced to VIH and VIL levels. Note 3: These parameters are guaranteed by design and are not tested. Refer to the Timing Diagrams for additional information.
TYPICAL PERFORMANCE CHARACTERISTICS
DNL vs Code
1.0 6 4 0.5 DNL (LSB)
INL (LSB)
0
-0.5
-1.0
0
512 CODE
1024
1247 G01
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INL vs Code
2 0 -2 -4 -6 -8 -10 0 512 CODE 1024
1247 G02
3
LTC1427-50 TYPICAL PERFORMANCE CHARACTERISTICS
Zero-Scale Current vs Temperature
0.02 0 -0.02
OUTPUT CURRENT (A) OUTPUT CURRENT (A)
-0.04 -0.06 -0.08 -0.10 -0.12 -0.14 -0.16 V (IOUT) = 0V -0.18 -50 -25 0 25 50 75 100 125 TEMPERATURE (C)
Bias Voltage Rejection (Zero-Scale Current)
4 ZERO-SCALE OUTPUT CURRENT (nA) FULL-SCALE OUTPUT ERROR (LSB) TA = 25C VCC = 3.3V 2 1.0
0
-2
-4 -15 -12
0 IOUT BIAS VOLTAGE (V)
-9
-6
Supply Voltage Rejection
2 FULL-SCALE OUTPUT ERROR (LSB) TA = 25C V(IOUT) = 0V 200
SHUTDOWN CURRENT (A)
SUPPLY CURRENT (A)
1
0
-1
-2
0
1
5 SUPPLY VOLTAGE (V)
2
3
4
4
UW
-3 6
1427 G07
Full-Scale Current vs Temperature
52 V(IOUT) = 0V 51
50
49
150
48 -50 -25
0
25
50
75
100 125
150
TEMPERATURE (C)
1427 G04
1427 G03
Bias Voltage Rejection (Full-Scale Current)
TA = 25C VCC = 3.3V 0.5
0
-0.5
3
6
-1.0 -15 -12
-9 -6 -3 0 IOUT BIAS VOLTAGE (V)
3
6
1427 G05
1427 G06
Supply Current vs Temperature
20
Shutdown Current vs Temperature
150 VCC = 5.5V
VCC = 3.3V
15 VCC = 5.5V 10 VCC = 2.7V 5
VCC = 3.3V
VCC = 2.7V 100
50
7
0 -50 -25
0
25 50 75 100 125 TEMPERATURE (C)
150
0 -50 -25
0
25 50 75 100 125 TEMPERATURE (C)
150
1527 G08
1527 G09
LTC1427-50
PIN FUNCTIONS
SHDN (Pin 1): Shutdown. A logic low puts the chip into shutdown mode. In shutdown, the digital settings for the DAC are retained. On release from shutdown, the previously programmed value for IOUT is reinstated. AD1, AD0 (Pins 2, 3): Address Selection Pins. Tie these two pins to either VCC or GND to select one of four SMBus addresses to which the LTC1427-50 will respond. GND (Pin 4): Ground. Ground should be tied directly to a ground plane. SDA (Pin 5): SMBus Bidirectional Data Input/Digital Output. This pin is an open-drain output and requires a pullup resistor or current source to VCC. Data is shifted into the SDA pin and acknowledged by the SDA pin. SCL (Pin 6): SMBus Clock Input. Data is shifted into the SDA pin at the rising edges of the SCL clock during data transfer. IOUT (Pin 7): DAC Current Output. VCC (Pin 8): Voltage Supply. This supply must be kept free from noise and ripple by bypassing directly to the ground plane.
FU CTIO TABLES
AD1 L L H H AD0 L H L H SMBus Address Location 0101101 0101111 0101110 0101100 DAC Power-Up Value Zero-Scale Zero-Scale Zero-Scale Midscale Application CCFL Backlight Control General Purpose General Purpose LCD Contrast Control
BLOCK DIAGRAM
SCL SDA SMBUS INTERFACE
AD0
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SHDN SD POWER-ON RESET
3
REGISTER A 3-BIT LATCH EN1
1
REGISTER B 1-BIT LATCH EN2 SHDN
VOLTAGE REFERENCE SD
RADJ
2 8
REGISTER C 10-BIT LATCH 10 EN2
SD 10-BIT CURRENT DAC IOUT
AD1
1427 BD
5
LTC1427-50 TI I G DIAGRA S
Timing for SMBus Interface
t BUF SDA
SCL t LOW STOP START t HIGH t HD:DAT t SU:STA t SU:DAT START t SU:STO
1427 TD01
AD1 GND VCC AD0 GND SMBUS ADDRESS
SHDN ACK
ACK
SDA
0
1
0
1
1
1
1
X
X
X
X
X
1
1
1
1
1
1
1
1
1
1
ACK
WR
SCL
S 1 2
3
4
5
6
IOUT S = START P = STOP * = OPTIONAL
1427 TD02
APPLICATIONS INFORMATION
Digital Interface The LTC1427-50 communicates with an SMBus host using the standard 2-wire SMBus interface. The Timing Diagram shows the signals on the SMBus. The SCL and SDA bus lines must be high when the bus is not in use. External pull-up resistors or current sources are required at these lines. The LTC1427-50 is a receive-only (slave) device. The master must apply the following Write Byte protocol to communicate with the LTC1427-50:
1 7 1 1 A 8 Command Byte 1 8 11 AP
S Slave Address WR
A Data Byte
S = Start Condition, WR = Write Bit, A = Acknowledge Bit, P = Stop Condition
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t HD:STA tr tf
t HD:STA
STOP
Operating Sequence SMBus Write Byte Protocol, with SMBus Address = 0101111B, Command Byte = 0XXXXX11B and Data Byte = 11111111B
VCC
COMMAND BYTE
DATA BYTE
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9
* P 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 FULL-SCALE CURRENT ZERO-SCALE CURRENT
The master initiates communication with the LTC1427-50 with a START condition (see SMBus Operating Sequence) and a 7-bit address followed by the write bit = 0. The LTC1427-50 acknowledges and the master delivers the command byte. The LTC1427-50 acknowledges and latches the active bits of the command byte into register A (see Block Diagram) at the falling edge of the acknowledge pulse. The master sends the data byte and the LTC142750 acknowledges the data byte. The data byte and last two output bits from register A are latched into register C at the falling edge of the final acknowledge pulse and the DAC current output assumes the new 10-bit data value (see Block Diagram). A STOP condition is optional. The com-
LTC1427-50
APPLICATIONS INFORMATION
mand code and data byte are defined with the following format:
Command Byte
7 6 54 XX 3 X 2 1 0 SHDN X X D9 D8
Data Byte
7 6 5 4 3 2 1 0 D7 D6 D5 D4 D3 D2 D1 D0
SHDN: 0 for Normal Operation, 1 for Shutdown D9 to D0: DAC Data Bits, D9 is the Most Significant Bit
START and STOP Conditions At the beginning of any SMBus communication, the master must transmit a START condition by switching the SDA from high to low while SCL is high. When a master has finished communicating with a slave device, a STOP condition is issued by switching the SDA from low to high while SCL is high. The SMBus is then free for communication with another SMBus slave device. Early STOP Conditions The LTC1427-50 recognizes a STOP condition at any point in the SMBus communication sequence. If the STOP occurs prematurely before the data byte is acknowledged in the Write Byte protocol, the DAC output current value is not updated; otherwise internal register C is updated with the new data and the DAC output current changes correspondingly.
TYPICAL APPLICATIONS
LTC1427-50 Used to Null Op Amp's Offset Voltage
RF RIN
VIN
LT1006
R2 100 V- R1 =
V - (0.5)(IFULL SCALE) TRIM RANGE = (0.5)(IFULL SCALE)(R2)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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The Slave Address The LTC1427-50 can respond to one of four 7-bit addresses. The first five bits have been factory programmed to 01011. The two address bits, AD1 and AD0, are programmed by the user (see Function Table). 10-Bit Current Output DAC The 10-Bit current output DAC is guaranteed monotonic and is digitally adjustable in 1023 equal steps. On powerup, if AD1 and AD0 are both connected to VCC, the 10-bit internal register C (see Block Diagram) resets to 1000000000B and the DAC output is set to midrange. If either AD1 or AD0 is connected to ground, register C resets to 0000000000B on power-up and the DAC output is set to zero. For the LTC1427-50, the source current output (IOUT) can be biased from - 15V to (VCC - 1.3V). Full-scale current is trimmed to 1.5% at room temperature and 2.5% over the commercial temperature range. Shutdown There are two ways to shut down the LTC1427-50 (see Block Diagram). The LTC1427-50 will enter shutdown mode whenever it sees a logic low at the SHDN pin or whenever it receives a logic high at bit 7 of the command byte through the SMBus interface. In shutdown mode, the digital data is retained internally and the supply current drops to only 10A typically.
VOUT
R1 600k
VCC
SHDN 1 2 3 4 8 7 6 5 TO SMBUS HOST
1427 TA03
SHDN AD1 AD0 GND
VCC IOUT SCL SDA
LTC1427-50
7
LTC1427-50
TYPICAL APPLICATIONS
SMBus-Controlled Floating CCFL Power Supply
UP TO 6mA LAMP ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3B WITH AN ESR 0.5 TO PREVENT DAMAGE TO THE LT1184F HIGH-SIDE SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON. C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKP-20 Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001 L1 = COILTRONICS CTX210605 L2 = COILTRONICS CTX100-4 *DO NOT SUBSTITUTE COMPONENTS COILTRONICS (407) 241-7876 0A TO 50A ICCFL CURRENT GIVES 0mA TO 6mA LAMP CURRENT FOR A TYPICAL DISPLAY. VCC 3.3V C6 0.1F 3 C5 1000pF R2 220k 10 6 C2 27pF 3kV L1 2 1 C3B 2.2F 35V 4 5
LTC1427-50 SHDN 1 2 3 4 SHDN AD1 AD0 GND VCC IOUT SCL SDA 8 7 6 5 TO SMBUS HOST 1 2 3 C7, 1F 4 5 6 7 8 CCFL PGND ICCFL DIO AGND SHDN NC NC CCFL VC CCFL VSW BULB LT1184F BAT VIN REF NC NC ROYER 16 15 14 13 12 11 10 9
PACKAGE DESCRIPTION
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
RELATED PARTS
PART NUMBER LTC1329-10/LTC1329-50 LTC1380/LTC1393 LTC1426 LTC1428 LTC1623 DESCRIPTION Micropower 8-Bit Current Source DAC SMBus Single-Ended 8-Channel/Differential 4-Channel Multiplexers Micropower Dual 6-Bit PWM DAC Micropower 8-Bit Current Sink DAC SMBus Dual High Side Switch Controller COMMENTS 1-Wire, 2-Wire or Standard 3-Wire SPI Control Single 2.7V to 5V Supply, Low Power Pulse Mode and Push-Button Mode Interface 1-Wire, 2-Wire or Standard 3-Wire SPI Control Regulated Onboard Charge Pump Drives External N-Channel MOSFETs
142750f LT/TP 0398 4K * PRINTED IN USA
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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R1 750
C3A 2.2F 35V
BAT 8V TO 28V
R3 100k D5 BAT85
Q2*
C1* 0.1F
Q1*
L2 100H
D1 1N5818
+
C4 2.2F
VIN 3.3V
1427 TA01
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.053 - 0.069 (1.346 - 1.752) 8 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 0.189 - 0.197* (4.801 - 5.004) 7 6 5
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
1
2
3
4
SO8 0996
(c) LINEAR TECHNOLOGY CORPORATION 1998

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