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LT1 120A Micropower Regulator with Comparator and Shutdown
FEATURES
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DESCRIPTION
The LT1120A is a combination micropower positive regulator and free collector comparator on a single monolithic chip. With only 20A supply current, the LT1120A can supply over 125mA of output current. Input voltage range is from 4.5V to 36V and dropout voltage is 0.6V at 125mA. Dropout voltage decreases with lower load currents. Also included on the chip is a class B output 2.5V reference that can either source or sink current. This allows it to be used as a supply splitter or auxiliary output. A shutdown pin allows logic shutdown of the output. The comparator can be used for system or battery monitoring. For example, the comparator can be used to warn of low system voltage. Frequency compensation of the comparator for amplifier applications can be obtained by adding external output capacitance.
20A Supply Current 8-Lead SOIC 125mA Output Current 2.5V Reference Reference Output Sources 4mA and Sinks 4mA Open Collector Comparator Sinks 10mA Logic Shutdown 0.2V Dropout Voltage Thermal Limiting
APPLICATIONS
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Battery Systems Battery Backup System Portable Terminals Portable Instruments Memory Keep Alive
TYPICAL APPLICATION
5V Regulator
1.00
Dropout Voltage and Supply Current
10
LT1120A
0.001F FB 2
1M
+
10F 3 SHUTDOWN
GND 1
+
25F 1M
DROPOUT VOLTAGE (V)
VIN > 5.2V IQ = 20A
5V IN
VOUT 4
5V
0.10
1120A TA01
0.01 0.1
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SUPPLY CURRENT (mA)
1
1 10 100 OUTPUT CURRENT (mA)
0.1 1000
1120A TA02
1
LT1 120A
ABSOLUTE MAXIMUM RATINGS
Input Voltage ........................................................... 36V NPN Collector Voltage ............................................. 36V Output Short-Circuit Duration .......................... Indefinite Power Dissipation............................... Internally Limited Operating Temperature Range LT1120AC .............................................. 0C to 100C Storage Temperature Range LT1120AC .......................................... -65C to 150C
PACKAGE/ORDER INFORMATION
TOP VIEW GND FEEDBACK SHUTDOWN VOUT 1 2 3 4 LT1120A 6 5 8 7 -INPUT COMP OUT REF VIN
ORDER PART NUMBER LT1120ACN8 LT1120ACS8 S8 PART MARKING 1120A
N8 PACKAGE 8-LEAD PLASTIC DIP
S8 PACKAGE 8-LEAD PLASTIC SOIC
1120A POI01
TJMAX = 110C, JA = 130C/ W (N) TJMAX = 110C, JA = 190C/ W (S)
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER Reference Reference Voltage Line Regulation Load Regulation Output Source Current Output Sink Current Temperature Stability Regulator Supply Current CONDITIONS
TJ = 25C
MIN 2.46 TYP
2.50
MAX 2.54 0.015 0.6
UNITS V %/V % mA mA % A A mA mA % %/V V V V V V A nA A mA mV nA V/V dB mA V V s A
4.5V VIN 36V 4.5V VIN 36V -2.0mA IREF 2mA, VIN = 12V VIN = 5V VIN = 5V
2 2
0.01 0.3 4 4 1 20 30 11
Output Current Load Regulation Line Regulation Dropout Voltage Feedback Sense Voltage Shutdown Pin Voltage Shutdown Pin Current Feedback Bias Current Minimum Load Current Short Circuit Current Comparator Offset Voltage Bias Current Gain Power Supply Rejection Output Sink Current Saturation Voltage Input Voltage Range Response Time Leakage Current
VIN = 6V, IOUT 100A VIN = 36V, IOUT 100A VIN = 12V, IOUT = 125mA (VIN - VOUT) 1V, VIN 6V (VIN - VOUT) 1V, VIN 6V 6V VIN 36V IOUT = 100A IOUT = 125mA VIN = 12V Normal VOUT 0.5V Shutdown VIN = 1.4V VIN = 36V VIN = 36V VIN = 36V VIN = 36V VOUT = 29V, RL = 20k 4.5V VS 36V VIN = 4.5V IOUT = 1mA
25 40 20 0.5 0.015 0.05 0.65 2.56 0.4
125 0.2 0.01 0.02 0.40 2.5 1.4 10 15 1 250 3 15 10000 96 18 0.4 5
2.44 2.2
40 5 400 7 40
2000 80 10 0
0.6 VIN - 1 2
VIN = 36V, V(Pin 7) = 36V
2
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LT1 120A
ELECTRICAL CHARACTERISTICS
PARAMETER Reference Reference Voltage Line Regulation Load Regulation Output Source Current Output Sink Current Regulator Supply Current CONDITIONS 4.5V VIN 36V 4.5V VIN 36V -2.0mA IREF 2mA, VIN = 12V VIN = 5V VIN = 5V VIN = 6V, IOUT 100A VIN = 36V, IOUT 100A VIN = 12V, IOUT = 125mA (VIN - VOUT) 1V, VIN 6V (VIN - VOUT) 1V, VIN 6V 6V VIN 36V IOUT = 100A IOUT = 125mA VIN = 12V VIN = 36V VIN = 36V VIN = 36V VIN = 36V VOUT = 29V, RL = 20k VIN = 4.5V VIN = 36V, V(Pin 7) = 36V
q q q q q q q q q q q q q q q q q q q q q q
MIN 2.40
TYP 2.50 0.01 0.4
MAX 2.55 0.02 0.8
UNITS V %/V % mA mA A A mA mA % %/V V V V nA A mA mV nA V/V mA A
2 2 30 40 11 125 1 0.02 0.06 0.85 2.57 50 50 400 10 60 40 50 20
Output Current Load Regulation Line Regulation Dropout Voltage Feedback Sense Voltage Feedback Bias Current Minimum Load Current Short Circuit Current Comparator Offset Voltage Bias Current Gain Output Sink Current (Note 1) Leakage Current
2.38
2.5
240
15 1000 5 10
8
The q denotes specifications which apply over the operating temperature range. Note 1: For TA -40C output sink current drops to 2.5mA.
TYPICAL PERFORMANCE CHARACTERISTICS
Regulator Load Regulation
0.3
OUTPUT VOLTAGE CHANGE (%)
PRE-LOAD = 100 A
T J = -55C
SUPPLY CURRENT (mA)
T J = 25C 0.1 0 T J = 125C -0.1 -0.2 -0.3 0.1
10
SHORT-CIRCUIT CURRENT (mA)
0.2
1 10 100 OUTPUT CURRENT (mA)
UW
1120A G01
Supply Current
100 350 300 250 200 150 100 50
Regulator Short-Circuit Current
1
0.1
1000
0.01 0.1
1 1000 10 100 REGULATOR OUTPUT CURRENT (mA)
1120A G02
0 -50
-10
110 30 70 TEMPERATURE (C)
150
1120A G03
3
LT1 120A TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Voltage
REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
1 VOUT = 100mV
MINIMUM LOAD CURRENT (A)
RIPPLE REJECTION (dB)
0.1
0.01 0.1
10 100 1 1000 REGULATOR OUTPUT CURRENT (mA)
1120A G04
Supply Current
10 I OUT = 100mA
SUPPLY CURRENT (mA)
REFERENCE VOLTAGE CHANGE (mV)
1
SUPPLY CURRENT (mA)
0.1
I OUT = 10mA
I OUT = 1mA 0.01
VOUT = 5V 0.01
5 1 10 25 15 20 REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
1120A G07
OUTPUT VOLTAGE CHANGE (%)
Feedback Pin Current
40 35
FEEDBACK PIN CURRENT (nA)
25 20 15 10 5 0 0.1 TJ = 125C TJ = 25C
OUTPUT VOLTAGE (V)
30
TJ = -55C
OUTPUT CURRENT (mA)
10 100 1 1000 REGULATOR OUTPUT CURRENT (mA)
1120A G10
4
UW
Regulator Minimum Load Current
100
70 65 60 55 50 45 40 35
Regulator Ripple Rejection
I OUT = 100mA
10
I OUT = 10mA I OUT = 1mA VIN = 10VDC, 1Vp-p VOUT = 5V COUT = 10F 10 100 10k 1k RIPPLE FREQUENCY (Hz) 100k
1120A G06
1 70
30
80
90
100 110 120 130 140 150 TEMPERATURE (C)
1120A G05
Supply Current at Dropout
10 I OUT = 100mA 1 4 3 2 1 0 -1 -2 -3
Reference Regulation
0.1
I OUT = 10mA
I OUT = 1mA 0.1 0 0.2 0.6 0.3 0.5 0.4 REGULATOR INPUT-OUTPUT DIFFERENTIAL (V)
1120A G08
-4 -1.5
-1.0 -0.5 0.5 1.0 0 REFERENCE OUTPUT CURRENT (mA)
1.5
1120A G09
Regulator Thermal Regulation
0.1 VIN = 15V VOUT = 5V 0
4.5 4.0 5.5 5.0
Turn-On Characteristic
VOUT = 5V NO LOAD
-0.1
RL = 500 3.5 3.0 2.5 2.0 RL = 50 0 1 2 3 4 5 6 INPUT VOLTAGE (V) 7 8
50
0 0 20 40 60 80 100 120 140 160 180 TIME (ms)
1120A G11
0
1120A G12
LT1 120A
PIN FUNCTIONS
Pin 1 (Ground). Pin 2 (Feedback): This is the feedback point of the regulator. When operating, it is nominally at 2.5V. Optimum source resistance is 200k to 500k. The feedback pin should not be driven below ground or more positive than 5V. Pin 3 (Shutdown): A logic 1 shuts off main regulator. Caution: noise or leakage into the shutdown pin can affect output voltage. Pin 4 (Regulator Output): Main output, requires 10F output capacitor. Can be shorted to VIN or ground without damaging device. Pin 5 (Input Supply): Bypass with 10F cap. Must always be more positive than ground. Pin 6 (Reference): 2.5V can source or sink current. May be shorted to ground or up to 5V. Voltages in excess of 5V can damage the device. Pin 7 (Comparator Output): May be connected to any voltage from ground to 36V more positive than ground (operates above VIN). Short circuit protected. Pin 8 (Comparator Input): Inverting comparator input.
BLOCK DIAGRAM
COMPARATOR OUT
APPLICATIONS INFORMATION
The LT1120A is especially suited for micropower system applications. For example, the comparator section of the LT1120A may be used as a battery checker to provide an indication of low battery. Another type of system application for the LT1120A would be to generate the equivalent of split supplies off of a single power input. The regulator section provides regulated output voltage and the reference, which can both source and sink current is then an artificial system ground providing a split supply for the system. For many applications the comparator can be frequency compensated to operate as an amplifier. Compensation values for various gains are given in the data sheet. The comparator gain is purposely low to make it easier to frequency compensate as an amplifier. The NPN output is capable of sinking 10mA and can drive loads connected to voltages in excess of the positive power supply. This is useful for driving switches or linear regulators off of a higher input voltage.
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REFERENCE 6 VIN 5 7
+ -
REF 2.5V
100k
4 2 120k 3 1
VOUT FEEDBACK SHUTDOWN GROUND
8 -INPUT
1120A BD01
5
LT1 120A
APPLICATIONS INFORMATION
Reference Internal to the LT1120A is a 2.5V trimmed class B output reference. The reference was designed to be able to source or sink current so it could be used in supply splitting applications as well as a general purpose reference for external circuitry. The design of the reference allows it to source and sink typically 4mA. The available source and sink current decreases as temperature increases. It is sometimes desirable to decrease the AC output impedance by placing an output capacitor on Pin 6. The reference in the LT1120A becomes unstable with large capacitive loads placed directly on it. When using an output capacitor, about 20 should be used to isolate the capacitor from the reference pin. This 20 resistor can be placed directly in series with the capacitor or alternatively the reference line can have 20 placed in series with it and then a capacitor to ground. This is shown in Figure 1. Other than placing large capacitive loads on the reference, no other precautions are necessary and the reference is stable with nominal stray capacitances.
REF 6 OUTPUT 20 REF 6 20
+
10F
OR
+
OUTPUT 10F
1120A AI01
Figure 1. Bypassing Reference
Overload Protection The main regulator in the LT1120A is current limited at approximately 250mA. The current limit is stable with both input voltage and temperature. Like most other IC regulators, a minimum load is required on the output of the LT1120A to maintain regulation. For
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most standard regulators this is normally specified at 5mA. Of course, for a micropower regulator this would be a tremendously large current. The output current must be large enough to absorb all the leakage current of the pass transistor at the maximum operating temperature. It also affects the transient response; low output currents have long recovery times from load transients. At high operating temperatures the minimum load current increases and having too low of a load current may cause the output to go unregulated. Devices are tested for minimum load current at high temperature. The output voltage setting resistors to the feedback terminal can usually be used to provide the minimum load current. Frequency Compensation The LT1120A is frequency compensated by a dominant pole on the output. An output capacitor of 10F is usually large enough to provide good stability. Increasing the output capacitor above 10F further improves stability. In order to ensure stability, a feedback capacitor is needed between the output pin and the feedback pin. This is because stray capacitance can form another pole with the large value of feedback resistors used with the LT1120A. Also, a feedback capacitor minimizes noise pickup and improves ripple rejection. With the large dynamic operating range of the output current, 10000:1, frequency response changes widely. Low AC impedance capacitors are needed to insure stability. While solid tantalum are best, aluminum electrolytics can be used but larger capacitor values may be needed.
LT1 120A
TYPICAL APPLICATIONS
Regulator with Output Voltage Monitor
5 5V LOGIC 500k 7 VIN OUTPUT 4 OUTPUT 5V 10F
LOGIC OUTPUT REF 6 LOGIC OUTPUT GOES LOW WHEN VOUT DROPS BY 100mV
Compensating the Comparator as an Op Amp
VREF
6
+ -
7 1M C2
50A
IN
R2
AT AV = 100, SLEW RATE = +0.05V/s - 6V/s R1 C1
AV -1 -10 -100
R1 33 100 10k
C1 0.1F 0.047F 0.002F
C2 R2 0.001F 1M - 100k - 10k
BATTERY INPUT
5
VIN LT1120A GND 1
INTERNAL PARASITIC DIODES OF LT1120A VIN VOUT
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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LT1120A 8 2
+
0.001F 98k 2k 100k
+
FEEDBACK GND 1
1120A TA03
Current Limited 1 Amp Regulator
2.2k MJE2955 5 VIN 0.22F VOUT 4 LT1120A GND 1 FB 2 270 100k 0.5* VIN 2N3906* VOUT 5V AT 1A 220F
+
1M
1120A TA04
* SETS CURRENT LIMIT BUT INCREASES DROPOUT VOLTAGE BY 0.5V.
MUST HAVE LOW
ESR. SEVERAL 100F CAPACITORS CAN BE PARALLELED.
1120A TA06
Battery Backup Regulator
VOUT 5V VOUT FB 4 4
+
0.001F 2 50k 1M 1M 10F 2
VOUT LT1120A FB GND 1
VIN
5
MAIN POWER INPUT
1120A TA05
7
LT1 120A
PACKAGE DESCRIPTION
0.300 - 0.320 (7.620 - 8.128)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0.016 - 0.050 0.406 - 1.270
0- 8 TYP
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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Dimension in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP
0.400 (10.160) MAX 8 7 6 5
0.250 0.010 (6.350 0.254)
1
2
3
4
0.045 - 0.065 (1.143 - 1.651)
0.130 0.005 (3.302 0.127)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.020 (0.508) MIN
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
N8 0392
S8 Package 8-Lead Plastic SOIC (Narrow)
0.189 - 0.197 (4.801 - 5.004) 8 7 6 5
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)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0392
LT/GP 0494 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

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