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Final Electrical Specifications
LT1790-2.5 2.5V Micropower SOT-23 Low Dropout Reference
March 2000
FEATURES
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DESCRIPTIO
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High Accuracy: A Grade--0.05% Max B Grade--0.1% Max Low Drift: A Grade--10ppm/C Max B Grade--25ppm/C Max Low Supply Current: 60A Max Sinks and Sources: 5mA Min Low Dropout Voltage Guaranteed Operational -40C to 125C Wide Supply Range: 2.6V to 18V
The LT(R)1790-2.5 is a SOT-23 micropower low dropout series reference that combines high accuracy and low drift with low power dissipation and small package size. This micropower reference uses curvature compensation to obtain a low temperature coefficient and trimmed precision thin-film resistors to achieve high output accuracy. In addition, the LT1790-2.5 uses post-package trimming to greatly reduce the temperature coefficient and increase the output accuracy. Output accuracy is further assured by excellent line and load regulation. Special care has been taken to minimize thermally induced hysteresis. The LT1790-2.5 is ideally suited for battery-operated systems because of its small size, low supply current and reduced dropout voltage. This reference provides supply current and power dissipation advantages over shunt references that must idle the entire load current to operate. However, since the LT1790-2.5 can also sink current, it can operate as a micropower negative voltage reference with the same performance as a positive reference.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Handheld Instruments Negative Voltage References Industrial Control Systems Data Acquisition Systems Battery-Operated Equipment
TYPICAL APPLICATIO
Typical VOUT Distribution
50 45 167 UNITS
NUMBER OF UNITS
Positive Connection
2.6V VIN 18V 0.1F 4 LT1790-2.5 1, 2 6 1F
1790 TA01
40 35 30 25 20 15 10 5 0 2.498
VOUT = 2.5V
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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LT1790BC LIMITS LT1790AC LIMITS 2.499 2.500 2.501 OUTPUT VOLTAGE (V) 2.502
1790 TA02
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LT1790-2.5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW GND 1 GND 2 DNC* 3 6 VOUT 5 DNC* 4 VIN
Input Voltage .......................................................... 20V Specified Temperature Range ..................... 0C to 70C Operating Temperature Range (Note 2) ........................................... - 40C to 125C Storage Temperature Range (Note 3) ........................................... - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT1790ACS6-2.5 LT1790BCS6-2.5 S6 PART MARKING LTMX LTMZ
S6 PACKAGE 6-LEAD PLASTIC SOT-23 TJMAX = 150C, JA = 230C/W *DNC: DO NOT CONNECT
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER Output Voltage (Notes 3, 4)
The q denotes specifications that apply over the specified temperature range, otherwise specifications are at TA = 25C. VIN = 3V, CL = 1F unless otherwise specified.
CONDITIONS LT1790ACS6-2.5 LT1790BCS6-2.5 Output Voltage Temperature Coefficient (Note 5) Line Regulation Load Regulation (Note 6) LT1790ACS6-2.5 LT1790BCS6-2.5 3V VIN 18V
q q q
MIN 2.49875 -0.05 2.4975 -0.1
TYP 2.50 2.50 5 12 50 80
MAX 2.50125 0.05 2.5025 0.1 10 25 170 220 160 250 110 100 400 250 60 75 125
UNITS V % V % ppm/C ppm/C ppm/V ppm/V ppm/mA ppm/mA ppm/mA mV mV mV A A A s VP-P VRMS ppm/kHr ppm ppm
IOUT Source = 5mA IOUT Source = 5mA IOUT Sink = 5mA VIN - VOUT, VOUT 0.1% IOUT = 0mA IOUT Source = 5mA IOUT Sink = 5mA VOUT = 2.5V
q
70
q q
Dropout Voltage (Note 7)
60 300 40 35
Supply Current Minimum Current Turn-On Time Output Noise (Note 8) Long-Term Drift of Output Voltage (Note 9) Hysteresis (Note 10)
q
VOUT = - 2.5V CLOAD = 1F 0.1Hz f 10Hz 10Hz f 1kHz T = 0C to 70C T = - 40C to 85C
q q
100 700 12 33 50 40 60
Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LT1790S6 is guaranteed functional over the operating temperature range of - 40C to 125C. Note 3: If the part is stored outside of the specified temperature range, the output voltage may shift due to hysteresis.
Note 4: ESD (Electrostatic Discharge) sensitive device. Extensive use of ESD protection devices are used internal to the LT1790, however, high electrostatic discharge can damage or degrade the device. Use proper ESD handling precautions.
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LT1790-2.5
ELECTRICAL CHARACTERISTICS
Note 5: Temperature coefficient is measured by dividing the change in output voltage by the specified temperature range. Incremental slope is also measured at 25C. Note 6: 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 7: Excludes load regulation errors. Note 8: Peak-to-peak noise is measured with a single pole highpass filter at 0.1Hz and a 2-pole lowpass filter at 10Hz. The unit is enclosed in a still air environment to eliminate thermocouple effects on the leads. The test time is 10 seconds. RMS noise is measured with a single pole highpass filter at 10Hz and a 2-pole lowpass filter at 1kHz. The resulting output is full-wave rectified and then integrated for a fixed period, making the final reading an average as opposed to RMS. A correction factor of 1.1 is used to convert from average to RMS and a second correction of 0.88 is used to correct for the nonideal bandpass of the filters. Note 9: Long-term drift typically has a logarithmic characteristic and therefore changes after 1000 hours tend to be smaller than before that time. Total drift in the second thousand hours is normally less than one third that to the first thousand hours with a continuing trend toward reduced drift with time. Long-term drift is affected by differential stress between the IC and the board material created during board assembly. See Applications Information. Note 10: Hysteresis in the 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 to 85C or - 40C before a successive measurements. Hysteresis is roughly proportional to the square of the temperature change. Hysteresis is not normally a problem for operational temperature excursions where the instrument might be stored at high or low temperature. See Applications Information.
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Temperature Drift
2.508 2.506 2.504 2.502 2.500 2.498 2.496 2.494 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
1790 G13
FOUR TYPICAL PARTS
TA = -55C
TA = 125C TA = 25C
VOLTAGE DIFFERENTIAL (mV)
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
Load Regulation (Sourcing)
0 OUTPUT VOLTAGE CHANGE (mV) TA = 25C TA = -55C OUTPUT VOLTAGE CHANGE (mV) 5
-1
-2
TA = 125C
SUPPLY CURRENT (A)
-3
-4
-5 0.1 1 OUTPUT CURRENT (mA)
UW
10
1790 616
Minimum Input-Output Voltage Differential (Sourcing) Series Mode
10
Minimum Input-Output Voltage Differential (Sinking) Series Mode
90 70 50 30 10 -10 -30 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
1790 G15
1
100A 1mA 5mA
0.1 0 0.1 0.2 0.3 0.4 0.5 INPUT-OUTPUT VOLTAGE (V) 0.6
1790 G14
Load Regulation (Sinking)
80 70
Supply Current vs Input Voltage
4
60 50
TA = -55C
3 TA = -55C 2 TA = 125C 1 TA = 25C 0 0.1 1 OUTPUT CURRENT (mA) 10
1790 617
TA = 25C 40 30 TA = 125C 20 10 0 0 5 10 INPUT VOLTAGE (V)
1790 G18
15
20
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LT1790-2.5 TYPICAL PERFOR A CE CHARACTERISTICS
Line Regulation
2.515 TA = 125C 2.510
OUTPUT VOLTAGE (V)
POWER SUPPLY REJECTION RATIO (dB)
OUTPUT IMPEDANCE ()
2.505 TA = 25C 2.500 2.495 2.490 2.489 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
1790 G19
TA = -55C
- 2.5V Characteristics
0.30
R1 10k 4 3V 6 VOUT 1F
0.25
CURRENT IN RL (mA)
0.20 0.15 0.10 0.05
-VEE
ppm
0 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 OUTPUT TO GROUND VOLTAGE (V)
Output Noise 0.1Hz to 10Hz
10
OUTPUT NOISE (5V/DIV)
NOISE VOLTAGE (V/Hz)
0
1
2
4
UW
3
Power Supply Rejection Ratio vs Frequency
20 10 0 -10 -20 -30 -40 -50 -60 -70 -80 100 1k 10k 100k FREQUENCY (Hz) 1M
1790 G20
Output Impedance vs Frequency
1000
CL = 1F CL = 0.47F CL = 1F 100
CL = 4.7F 10
1 100
1k 10k FREQUENCY (Hz)
100k
1790 G21
Long-Term Drift (Data Points Reduced After 500 Hr)
140 TA = 30C 120 2 TYPICAL PARTS SOLDERED TO PCB 100 80 60 40 20 0
LT1790-2.5 1, 2 RL 5k
TA = 25C TA = 125C TA = -55C 0
-20 -40 -60 0 200 600 400 HOURS 800 1000
1790 G23
1790 G22
Output Voltage Noise Spectrum
CL = 1F
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IO = 0A IO = 100A IO = 250A
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2 IO = 1mA 0
456 TIME (SEC)
7
8
9
10
10
100 1k FREQUENCY (Hz)
10k
1790 G25
1790 G24
LT1790-2.5
APPLICATIONS INFORMATION
Bypass and Load Capacitors The LT1790-2.5 voltage reference should have an input bypass capacitor of 0.1F or larger, however the bypassing of other local devices may serve as the required component. This reference also requires an output capacitor for stability. The optimum output capacitance for most applications is 1F, although larger values work as well. This capacitor affects the turn-on and settling time for the output to reach its final value. Figure 1 shows the turn-on time for the LT1790-2.5 with a 1F input bypass and 1F load capacitor. Figure 2 shows the output response to a 0.5V transient on VIN with the same capacitors.
VGEN 3V 2V
3V 2V 1V 0V
1790 F01
Figure 1. Turn-On Characteristics of LT1790-2.5
3V 2V 1V 0V
1790 F02
Figure 2. Output Response to 0.5V Ripple on VIN
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VIN VIN
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The test circuit of Figure 3 is used to measure the stability of various load currents. With RL = 1k, the 1V step produces a current step of 1mA. Figure 4 shows the response to a 0.5mA load. Figure 5 is the output response to a sourcing step from 4mA to 5mA, and Figure 6 is the output response of a sinking step from - 4mA to - 5mA.
VIN 3V 4 CIN 0.1F 6 CL 1F 1k VGEN 1V
1790 F03
LT1790-2.5 1, 2
Figure 3. Response Time Test Circuit
VOUT
VOUT
1790 F04
Figure 4. LT1790-2.5 Sourcing and Sinking 0.5mA
VOUT
VOUT VGEN -2V -3V
1790 F05
Figure 5. LT1790-2.5 Sourcing 4mA to 5mA
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LT1790-2.5
APPLICATIONS INFORMATION
VGEN 8V
6V
4V
VOUT
2V
0V
1790 F06
Figure 6. LT1790-2.5 Sinking - 4mA to - 5mA
Positive or Negative Operation Series operation is ideal for extending battery life. If the LT1790-2.5 is operated in series mode it does not require an external current setting resistor. The specifications guarantee the LT1790-2.5 operates from 2.6V to 18V. When the circuitry being regulated does not demand current, the series connected LT1790-2.5 consumes only a few hundred W, yet the same connection can sink or source 5mA of load current when demanded. A typical series connection is shown on the front page of this data sheet. The circuit in Figure 7 shows the connection for a - 2.5V reference. The LT1790-2.5 can be used as a very stable negative reference, however, it requires a positive voltage applied to Pin 4 to bias internal circuitry. This voltage must be current limited with R1 to keep the output PNP
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V - 2.5V RL = EE 125A VEE
Figure 7. Using the LT1790-2.5 to Build a -2.5V Reference
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transistor from turning on and driving the grounded output. C1 provides stability during load transients. This connection maintains the accuracy and temperature coefficient of the positive connected LT1790-2.5. Long-Term Drift Long-term drift cannot be extrapolated from accelerated high temperature testing. This erroneous technique gives drift numbers that are widely optimistic. The only way long-term drift can be determined is to measure it over the time interval of interest. The LT1790S6 drift data was taken on over 100 parts that were soldered into PC boards similar to a "real world" application. The boards were then placed into a constant temperature oven with TA = 30C, their outputs scanned regularly and measured with an 8.5 digit DVM. Long-term drift curves are shown in the Typical Performance Characteristics. Hysteresis Hysteresis data shown in Figures 8 and 9 represent the worst-case data taken on parts from 0C to 70C and from - 40C to 85C. Units were cycled several times over these temperature ranges and the largest change is shown. As expected, the parts cycled over the higher temperature range have higher hysteresis than those cycled over the lower range. When the LT1790-2.5 is IR reflow soldered onto a PC board, the output shift is typically just 150ppm (0.015%).
R1 10k 3V 4 LT1790-2.5 1, 2 VOUT = -2.5V CL 1F
1790 F07
C1 0.1F
LT1790-2.5
APPLICATIONS INFORMATION
16 14 12 12 11 10 9
NUMBER OF UNITS
NUMBER OF UNITS
10 8 6 4 2 0
70C TO 25C
0C TO 25C
-50
-30
-10
10
30 50 70 HYSTERESIS (ppm)
90
110
Figure 8. Worst-Case 0C to 70C Hysteresis on 44 Units
SI PLIFIED SCHEMATIC
4 VIN
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8 7 6 5 4 3 2 1 0
85C TO 25C
-40C TO 25C
130
1790 F08
-100 -80
-60
-40
-20 20 40 0 HYSTERESIS (ppm)
60
80
100
120
1790 F09
Figure 9. Worst-Case -40C to 85C Hysteresis on 44 Units
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6 VOUT
1, 2 GND
1790 SS
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LT1790-2.5
TYPICAL APPLICATION
- 2.5V Negative 50mA Series Reference No Load Supply Current ICC = 1.6mA IEE = 440A
VCC = 5V 2k 4 VZ = 5.1V 5.1k LT1790-2.5 1, 2 6
PACKAGE DESCRIPTION
2.6 - 3.0 (0.110 - 0.118) 1.50 - 1.75 (0.059 - 0.069) 0.00 - 0.15 (0.00 - 0.006) 0.90 - 1.45 (0.035 - 0.057) 2.80 - 3.00 (0.110 - 0.118) (NOTE 3)
0.35 - 0.55 (0.014 - 0.022)
0.09 - 0.20 (0.004 - 0.008) (NOTE 2)
NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
RELATED PARTS
PART NUMBER LT1019 LT1027 LT1236 LTC(R)1798 LT1460 LT1461 LT1634 DESCRIPTION Precision Reference Precision 5V Reference Precision Reference Micropower Low Dropout Reference Micropower Precison Series Reference Micropower Precision Low Dropout Reference Micropower Precision Shunt Voltage Reference COMMENTS Bandgap, 0.05%, 5ppm/C Lowest TC, High Accuracy, Low Noise, Zener Based 5V and 10V Zener-Based 5ppm/C, SO-8 Package 0.15% Max, 6.5A Supply Current Bandgap, 130A Supply Current, 10ppm/C, Available in SOT-23 Bandgap 0.04%, 3ppm/C, 50A Max Supply Current Bandgap, 0.05%, 10ppm/C, 10A Supply Current
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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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VEE = -5V MPS2907A 1F
-2.5V 50mA
1790 TA03
Dimensions in inches (millimeters) unless otherwise noted. S6 Package 6-Lead Plastic SOT-23
(LTC DWG # 05-08-1634)
PIN 1 0.35 - 0.50 0.90 - 1.30 (0.014 - 0.020) (0.035 - 0.051) SIX PLACES (NOTE 2) 1.90 (0.074) REF 0.95 (0.037) REF
S6 SOT-23 0898
179025i LT/TP 0300 4K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 2000

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