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LTC1798 Series Micropower Low Dropout References
FEATURES
s s s s s s s
DESCRIPTIO
200mV Max Dropout at 10mA Output Current 4A Typical Quiescent Current 0.15% Max Initial Accuracy No Output Capacitor Required Output Sources 10mA, Sinks 2mA 40ppm/C Max Drift Voltage Options: 2.5V, 3V, 4.1V, 5V and Adjustable
The LTC(R)1798/LTC1798-2.5/LTC1798-3/LTC1798-4.1/ LTC1798-5 are micropower bandgap references that combine high accuracy and low drift with very low supply current and small package size. The combination of ultralow quiescent current and low dropout voltage of only 200mV (max) makes them ideal for battery-powered equipment. The output voltage is set by an external resistor divider for the adjustable LTC1798. This series of references uses curvature compensation to obtain low temperature coefficient and trimmed thin-film resistors to achieve high output accuracy. These references can source up to 10mA and sink up to 2mA, making them ideal for precision regulator applications. They are stable without an output bypass capacitor, but are also stable with capacitance up to 1F. This feature is important in critical applications where PC board space is a premium and fast settling is demanded. The LTC1798 series references provided power dissipation advantages over shunt references. In addition to supply current, shunt references must also idle the entire load current to operate. The LTC1798 series is available in the SO-8 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Battery-Powered Systems Handheld Instruments Precision Power Supplies A/D and D/A Converters
TYPICAL APPLICATIO
LTC1798-2.5 Temperature Drift 2.5V Battery-Powered Reference
LTC1798-2.5 2.7V TO 12.6V 2 0.1F GND
1798 TA01
4 REFERENCE VOLTAGE CHANGE (mV) 3 2 1 0 -1 -2 -3 -4 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
IN
OUT
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2.5V
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1798 TA02
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LTC1798 Series
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW *DNC 1 IN 2 **DNC/FB 3 GND 4 8 7 6 5 DNC* DNC* OUT DNC*
Supply Voltage ....................................................... 13V Input Voltages .......................................... - 0.3v to 13V Output Voltages ........................................ - 0.3V to 13V Output Short-Circuit Duration .......................... Indefinite Operating Temperature Range (Note 2) ........................................... - 40C to 100C Specified Temperature Range ..................... 0C to 70C Storage Temperature Range (Note 3) ... - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LTC1798CS8 LTC1798CS8-2.5 LTC1798CS8-3 LTC1798CS8-4.1 LTC1798CS8-5 S8 PART MARKING 1798 179825 17983 179841 17985
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 190C/W * CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS ** DNC FOR LTC1798-2.5/LTC1798-3/ LTC1798-4.1/LTC1798-5, FB FOR LTC1798
Consult factory for parts specified with wider operating temperature range.
AVAILABLE OPTIO S
OUTPUT VOLTAGE (V) 2.5 3 4.096 5 Adjustable TEMPERATURE RANGE (C) 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 ACCURACY (%) 0.15 0.15 0.15 0.15 0.4 TEMPERATURE COEFFICIENT (ppm/C) 40 40 40 40 40 PACKAGE TYPE SO-8 (S8) ORDER NUMBER PART MARKING LTC1798CS8-2.5 LTC1798CS8-3 LTC1798CS8-4.1 LTC1798CS8-5 LTC1798CS8 179825 17983 179841 17985 1798
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25C. VIN = VOUT(NOMINAL) + 0.2V, IOUT = 0mA unless otherwise noted. FB = OUT for the LTC1798.
SYMBOL VIN IIN VOUT PARAMETER Input Voltage Range Input Current Output Voltage (Note 4) FB = OUT for LTC1798
q
CONDITIONS
q
MIN
TYP 4.0
MAX 12.6 6.5 8.5 2.3945 0.4 2.5037 3.0045 4.102 5.0075 0.15
UNITS V A A V % V V V V %
LTC1798, FB = OUT LTC1798 ADJ LTC1798-2.5 LTC1798-3 LTC1798-4.1 LTC1798-5 LTC1798 All Fixed Options
2.3755 - 0.4 2.4963 2.9955 4.090 4.9925 - 0.15
2.385 2.5 3 4.096 5
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LTC1798 Series
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full specified temperature range, otherwise specifications are at TA = 25C. VIN = VOUT(NOMINAL) + 0.2V, IOUT = 0mA unless otherwise noted. FB = OUT for the LTC1798.
SYMBOL en TC VOUT/VIN VOUT/IOUT PARAMETER Output Voltage Noise (Note 5) Output Voltage Temp Coefficient (Note 6) Line Regulation Load Regulation (Note 7) CONDITIONS 0.1Hz f 10Hz TMIN TJ TMAX VIN = (VOUT(NOMINAL) + 0.2V) to 12.6V Sourcing 0mA to 10mA Sinking 0mA to 2mA
q q q q
MIN
TYP 8 15 30 0.1 1.75
MAX 40 120 0.3 4.0 6.5
UNITS ppmP-P ppm/C ppm/V mV/mA mV/mA mV/mA mA mA
ISC VDO VHYST IFB
Short-Circuit Output Current Dropout Voltage (Note 8) Output Hysteresis (Note 9) FB Pin Input Current
VOUT Shorted to GND VOUT Shorted to VIN IOUT = 0, VOUT 0.1% IOUT = 10mA, VOUT 0.1% T = - 40C to 85C T = 0C to 70C LTC1798, OUT = FB
q q
20 2
40 4 100 200 200 50 10
mV mV ppm ppm nA
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC1798 is guaranteed functional over the operating temperature range of - 40C to 100C. Note 3: If the part is stored outside of the specified operating temperature range, the output may shift due to hysteresis. Note 4: ESD (Electostatic Discharge) sensitive device. Extensive use of ESD protection devices are used internal to the LTC1798, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions. Note 5: Peak-to-peak noise is measured with a single pole highpass filter at 0.1Hz and 2-pole lowpass filter at 10Hz.
Note 6: Temperature coefficient is the change in output voltage divided by the nominal output voltage divided by the specified temperature range. Note 7: Load regulation is measured on a pulse basis from no load to the specified load current. Output changes due to die temperature change must be taken into account separately. Note 8: Dropout voltage is (VIN - VOUT) when VOUT falls to 0.1% below its nominal value at VIN = VOUT + 0.5V. Note 9: Hysteresis in output voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25C, but the IC is cycled hot or cold before successive measurements. Hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature.
TYPICAL PERFOR A CE CHARACTERISTICS
LTC1798-2.5* Dropout Voltage vs Output Source Current
100 90
DROPOUT VOLTAGE (mV)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
TA = 25C
80 70 60 50 40 30 20 10 0 0 1 10 0.1 OUTPUT SOURCE CURRENT (mA) 100
1798 G01
INPUT CURRENT (A)
*Similar performance characteristics can be expected for all voltage options.
UW
LTC1798-2.5* Input Current vs Temperature
8 VIN = 2.7V 7 6 5 4 3 2 1 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
1798 G02
LTC1798 Series Output ShortCircuit Current vs Temperature
70 60 50 40 30 20 10 5 0 -50 -25 0 OUTPUT SHORTED TO VIN 25 50 75 100 125 150 TEMPERATURE (C)
1798 G03
TA = 25C VIN = VOUT(NOM) + 0.2V
OUTPUT SHORTED TO GND
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LTC1798 Series TYPICAL PERFOR A CE CHARACTERISTICS
LTC1798-2.5* Output Short-Circuit Current vs Input Voltage
25
OUTPUT SHORT-CIRCUIT CURRENT (mA)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
VOUT FROM NO LOAD (mV)
20
TA = 25C OUTPUT SHORTED TO VIN
15
10
5
0 2 4 6 8 10 INPUT VOLTAGE (V) 12 14
1258-G04
LTC1798-2.5* Output Voltage vs Input Voltage
2.5010 TA = 25C 7
POWER SUPPLY REJECTION RATIO (dB)
OUTPUT VOLTAGE (V)
2.5005
INPUT CURRENT (A)
2.5000
2.4995
2
4
6 8 10 INPUT VOLTAGE (V)
LTC1798-2.5 0.1Hz to 10Hz Noise
1400
VIN = 2.7V
INPUT CURRENT (A)
INPUT CURRENT (A)
5V/DIV
1SEC/DIV
1798 G10
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UW
12
LTC1798-2.5* Output Short-Circuit Current vs Input Voltage
42 5 4 3 2 1 0 -1 -2 -3 -4 12 14
1798 G05
LTC1798 Series Load Regulation
TA = 25C VIN = VOUT(NOM) + 0.2V SINKING
SOURCING
TA = 25C OUTPUT SHORTED TO GND 41 2 4 6 8 10 INPUT VOLTAGE (V)
-5
0
1 10 0.1 OUTPUT CURRENT (mA)
100
1798 G06
LTC1798-2.5* Input Current vs Input Voltage
60
LTC1798-2.5 PSRR vs Frequency
VIN = 2.7V 50 40 30 20 10 0
TA = 25C
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5
14
1798 G07
4
2
4
6 8 10 INPUT VOLTAGE (V)
12
14
1798 G08
10
1k 100 FREQUENCY (Hz)
10k
1798 G09
LTC1798-5 Input Current vs Input Voltage in Dropout
250 TA = -55C TA = 25C 1000 TA = 125C 800 600 400 200 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 0 200
LTC1798-2.5 Input Current vs Input Voltage in Dropout
1200
TA = 125C 150
TA = 25C
100 TA = -55C 50
0
0.5
1
1.5 2 2.5 3 3.5 INPUT VOLTAGE (V)
4
4.5
5
1798 G11
1798 G12
LTC1798 Series
PI FU CTIO S
DNC (Pins 1, 5, 7, 8): Do Not Connect. Connected internally for post package trim. These pins must be left unconnected. IN (Pin 2): Positive Supply. Bypassing with a 0.1F capacitor is recommended if the output loading changes. (VOUT + 0.2V) VIN 12.6V. DNC (Pin 3): (LTC1798-2.5/LTC1798-3/LTC1798-4.1/ LTC1798-5) Do Not Connect. Connected internally for post package trim. This pin must be left unconnected. FB (Pin 3): (LTC1798) Resistor Divider Feedback Pin. Connect a resistor divider from OUT to GND and the center tap to FB. This pin sets the output potential. R1 + R2 VOUT = 2.385V ; R1 is connected from OUT R2 to FB and R2 from FB to GND. Selecting R2 10k will make IOUT < 250A. GND (Pin 4): Negative Supply or Ground Connection. OUT (Pin 6): Reference Output. The output can source up to 10mA and sink up to 2mA. It is stable with output bypass capacitor ranging from 0F to 1F.
BLOCK DIAGRA
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2 IN
+
OUT 6
2.385V
-
R1 FB 3 (LTC1798) R2
GND 4
1798 BD
NOTE: R1 AND R2 ARE NOT CONNECTED FOR LTC1798
5
LTC1798 Series
APPLICATIO S I FOR ATIO
Longer Battery Life Series references have an advantage over shunt style references. To operate, shunt references require a resistor between the power supply and the output. This resistor must be chosen to supply the maximum current that is demanded by the circuit being regulated. When the circuit being controlled is not operating at this maximum current, the shunt reference must always sink this current, resulting in high power dissipation and short battery life. The LTC1798 series low dropout references do not require a current setting resistor and can operate with any supply voltage from (VOUT(NOMINAL) + 0.2V) to 12.6V. When the circuitry being regulated does not demand current, the LTC1798 series reduces its dissipation and battery life is extended. If the reference is not delivering load current it dissipates only 10.8W when operating on a 2.7V supply for LTC1798-2.5, yet the same connection can deliver 10mA of load current when demanded. Output Bypass Capacitor The LTC1798 series is designed to be stable with or without capacitive loads. With no capacitive load, the reference is ideal for fast settling applications, or where PC board space is at a premium. In applications with significant output loading changes, an output bypass capacitor of up to 1F can be used to improve the output transient response. Figure 1 shows the response of the reference to a 1mA to 0A load step with a 1F output capacitor. If more than 1F of output
RESISTOR VALUE ()
1mA IOUT 0mA VOUT 100mV/DIV IOUT
10ms/DIV
1798 F01a
Figure 1. Reference Output Load Transient Response, 1F Output Capacitor
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capacitance is required, a resistor in series with the capacitor is recommended to reduce the output ringing. Figure 2 illustrates the use of a damping resistor for capacitive loads greater than 1F. Figure 3 shows the resistor and capacitor values required to achieve critical damping.
LTC1798-5 5.2V TO 12.6V 0.1F 2 IN GND 4 OUT 6 5V COUT >1F DAMPING RESISTOR <1k
1798 F02
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Figure 2. Adding a Damping Resistor with Output Capacitors Greater Than 1F
10k
1k
100
10 1 10 100 OUTPUT CAPACITOR VALUE (F) 1000
1798 F03
Figure 3. Damping Resistance vs Output Capacitor Value
1mA 0mA VOUT 100mV/DIV
0.5ms/DIV
1798 F01b
LTC1798 Series
APPLICATIO S I FOR ATIO
Internal P-Channel Pass Transistor The LTC1798 series features an internal P-channel MOSFET pass transistor. This provides several advantages over similar designs using a PNP bipolar pass transistor.
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.014 - 0.019 (0.355 - 0.483) TYP *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
0.016 - 0.050 (0.406 - 1.270)
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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These references consume only 4A of quiescent current under light and heavy loads as well as in dropout; whereas, PNP-based references waste considerable amounts of current when the pass transistor is saturated. In addition, the LTC1798 series provides a lower dropout voltage (200mV max) than PNP-based references.
0.228 - 0.244 (5.791 - 6.197) 0.150 - 0.157** (3.810 - 3.988) 1 2 3 4 0.053 - 0.069 (1.346 - 1.752) 0.004 - 0.010 (0.101 - 0.254) 0.050 (1.270) BSC
SO8 1298
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LTC1798 Series
TYPICAL APPLICATIO S
Micropower Low Dropout Negative Reference
2 IN 6 8 1 0.1F OUT LTC1798-3 GND 4 VOUT = - 3V
1798 TA03
2
- +
1/2 LTC1542 3 4
VSS = - 4V
Low Power, Low Voltage Supply Reference for LTC1096L
ANALOG INPUT 0V TO 3V RANGE
RELATED PARTS
PART NUMBER LT(R)1389 LT1634 LT1460 LT1461 LT1790 DESCRIPTION Nanopower Precision Shunt Voltage Reference Micropower Precision Shunt Voltage Reference Micropower Series Reference Micropower Precision Series Voltage Reference SOT-23, LDO Precision Micropower Reference COMMENTS 800nA Quiescent Current, 0.05% Max, 10ppm/C Max Drift 1.25V and 2.5V Versions, SO-8 Package 0.05% Max, 25ppm/C Max Drift, 1.25V, 2.5V, 4.096V and 5V Outputs 0.075% Max, 10ppm/C Max Drift, 2.5V, 5V and 10V Outputs 0.04% Max, 3ppm/C Max Drift, 35A Quiescent Current 0.05% Max, 10ppm/C Max, 2.5V, 60A Supply
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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Supply Splitter
0.2V VCC 8.5V
LTC1798-2.5 VCC = 5V 2 0.1F GND 4 IN OUT 6 2.5V VIRTUAL 0.1F GROUND
1798 TA04
1 CS/ VCC 2 SHDN +IN CLK LTC1096L 3 -IN DOUT 4 GND VREF
8 7 6 5
1F
MPU SERIAL DATA LINK (MICROWIRETM AND SPI COMPATIBLE)
SERIAL DATA LINK
6 OUT 4 GND LTC1798-3 IN 2 VIN 3.2V TO 0.1F 12.6V
1798 TA05
MICROWIRE is a trademark of National Semiconductor Corporation.
1798fa LT/LCG 1100 2K REV A * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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