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LT1121/LT1121-3.3/LT1121-5 Micropower Low Dropout Regulators with Shutdown
FEATURES

DESCRIPTIO
0.4V Dropout Voltage 150mA Output Current 30A Quiescent Current No Protection Diodes Needed Adjustable Output from 3.75V to 30V 3.3V and 5V Fixed Output Voltages Controlled Quiescent Current in Dropout Shutdown 16A Quiescent Current in Shutdown Stable with 0.33F Output Capacitor Reverse Battery Protection No Reverse Current with Input Low Thermal Limiting Available in the 8-Lead SO, 8-Lead PDIP, 3-Lead SOT-23 and 3-Lead TO-92 Packages
The LT(R)1121/LT1121-3.3/LT1121-5 are micropower low dropout regulators with shutdown. These devices are capable of supplying 150mA of output current with a dropout voltage of 0.4V. Designed for use in batterypowered systems, the low quiescent current, 30A operating and 16A in shutdown, makes them an ideal choice. The quiescent current is well-controlled; it does not rise in dropout as it does with many other low dropout PNP regulators. Other features of the LT1121/LT1121-3.3/LT1121-5 include the ability to operate with very small output capacitors. They are stable with only 0.33F on the output while most older devices require between 1F and 100F for stability. Small ceramic capacitors can be used, enhancing manufacturability. Also the input may be connected to ground or a reverse voltage without reverse current flow from output to input. This makes the LT1121 series ideal for backup power situations where the output is held high and the input is at ground or reversed. Under these conditions only 16A will flow from the output pin to ground.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Low Current Regulator Regulator for Battery-Powered Systems Post Regulator for Switching Supplies
TYPICAL APPLICATIO
8 1
5V Battery-Powered Supply with Shutdown
0.5
IN OUT LT1121-3.3 5 SHDN GND 3 3.3VOUT 150mA DROPOUT VOLTAGE (V)
5V
+
0.4
1F SOLID TANTALUM
0.3
0.2
VSHDN (PIN 5) OUTPUT <0.25 OFF >2.8 ON NC ON
0.1
LT1121 * TA01
0
0
20
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Dropout Voltage
40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
LT1121 * TA02
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LT1121/LT1121-3.3/LT1121-5
ABSOLUTE
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RATI GS (Note 1)
Output Short-Circuit Duration ......................... Indefinite Operating Junction Temperature Range (Note 3) LT1121C-X ........................................... 0C to 125C LT1121I-X ....................................... - 40C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
Input Voltage LT1121 ............................................................. 30V LT1121HV ............................................. +36V, - 30V Output Pin Reverse Current ................................. 10mA Adjust Pin Current ............................................... 10mA Shutdown Pin Input Voltage (Note 2) ........ 6.5V, - 0.6V Shutdown Pin Input Current (Note 2) .................. 20mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW OUT 1 NC/ADJ* 2 GND 3 NC 4 N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO 8 IN 7 NC** 6 NC** 5 SHDN
TJMAX = 150C, JA 120C/ W (N8, S8) TJMAX = 150C, JA 70C/ W (AS8)
* PIN 2 = NC FOR LT1121-3.3/LT1121-5 = ADJ FOR LT1121 ** PINS 6 AND 7 ARE FLOATING (NO INTERNAL CONNECTION) ON THE STANDARD S8 PACKAGE. PINS 6 AND 7 CONNECTED TO GROUND ON THE A VERSION OF THE LT1121 (S8 ONLY). CONNECTING PINS 6 AND 7 TO THE GROUND PLANE WILL REDUCE THERMAL RESISTANCE. SEE THERMAL RESISTANCE TABLES IN THE APPLICATIONS INFORMATION SECTION.
ORDER PART NUMBER LT1121CN8 LT1121CN8-3.3 LT1121CN8-5 LT1121IN8 LT1121IN8-3.3 LT1121IN8-5 LT1121CS8 LT1121CS8-3.3 LT1121CS8-5 LT1121HVCS8 LT1121IS8 LT1121IS8-3.3 LT1121IS8-5 LT1121HVIS8 LT1121ACS8 LT1121ACS8-3.3 LT1121ACS8-5 LT1121AHVCS8 LT1121AIS8 LT1121AIS8-3.3 LT1121AIS8-5 LT1121AHVIS8
S8 PART MARKING 121I3 121I5 121HVI 1121A 121A3 121A5 1121 121AHV 11213 121AI 11215 121AI3 1121HV 121AI5 1121I 21AHVI
Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges.
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FRONT VIEW 3 TAB IS GND 2 1 OUTPUT
BOTTOM VIEW
IN
GND VIN
GND
OUT
ST PACKAGE 3-LEAD PLASTIC SOT-223
Z PACKAGE 3-LEAD PLASTIC TO-92 TJMAX = 150C, JA 150C/ W
TJMAX = 150C, JA 50C/ W
ORDER PART NUMBER LT1121CST-3.3 LT1121IST-3.3 LT1121CST-5 LT1121IST-5
ST PART MARKING 11213 121IS3 11215 1121I5
ORDER PART NUMBER LT1121CZ-3.3 LT121IZ-3.3 LT1121CZ-5 LT1121IZ-5
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LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
range, otherwise specifications are at TA = 25C.
PARAMETER Regulated Output Voltage (Note 4) CONDITIONS LT1121-3.3 LT1121-5 LT1121 (Note 5) Line Regulation LT1121-3.3 LT1121-5 LT1121 (Note 5) Load Regulation LT1121-3.3 LT1121-5 LT1121 (Note 5) Dropout Voltage (Note 6) VIN = 3.8V, IOUT = 1mA, TJ = 25C 4.3V < VIN < 20V, 1mA < IOUT < 150mA VIN = 5.5V, IOUT = 1mA, TJ = 25C 6V < VIN < 20V, 1mA < IOUT < 150mA VIN = 4.3V, IOUT = 1mA, TJ = 25C 4.8V < VIN < 20V, 1mA < IOUT < 150mA VIN = 4.8V to 20V, IOUT = 1mA VIN = 5.5V to 20V, IOUT = 1mA VIN = 4.3V to 20V, IOUT = 1mA ILOAD = 1mA to 150mA, TJ = 25C ILOAD = 1mA to 150mA ILOAD = 1mA to 150mA, TJ = 25C ILOAD = 1mA to 150mA ILOAD = 1mA to 150mA, TJ = 25C ILOAD = 1mA to 150mA

The denotes specifications which apply over the operating temperature
MIN 3.250 3.200 4.925 4.850 3.695 3.640 TYP 3.300 3.300 5.000 5.000 3.750 3.750 1.5 1.5 1.5 - 12 - 20 - 17 - 28 - 12 - 18 0.13 0.30
MAX 3.350 3.400 5.075 5.150 3.805 3.860 10 10 10 - 25 - 40 - 35 - 50 - 25 - 40 0.16 0.25 0.35 0.50 0.45 0.60 0.55 0.70 50 120 500 2.5 7.0 14.0 300 2.8 10 22
UNITS V V V V V V mV mV mV mV mV mV mV mV mV V V V V V V V V A A A mA mA mA nA V V A A dB
ILOAD = 1mA, TJ = 25C ILOAD = 1mA ILOAD = 50mA, TJ = 25C ILOAD = 50mA ILOAD = 100mA, TJ = 25C ILOAD = 100mA ILOAD = 150mA, TJ = 25C ILOAD = 150mA
0.37
0.42

Ground Pin Current (Note 7)
ILOAD = 0mA ILOAD = 1mA ILOAD = 10mA ILOAD = 50mA ILOAD = 100mA ILOAD = 150mA
30 90 350 1.5 4.0 7.0 150 0.25 1.2 0.75 6 16 50 58 200
Adjust Pin Bias Current (Notes 5, 8) Shutdown Threshold Shutdown Pin Current (Note 9) Quiescent Current in Shutdown (Note 10) Ripple Rejection Current Limit Input Reverse Leakage Current Reverse Output Current (Note 11)
TJ = 25C VOUT = Off to On VOUT = On to Off VSHDN = 0V VIN = 6V, VSHDN = 0V VIN - VOUT = 1V (Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 0.1A VIN - VOUT = 7V, TJ = 25C VIN = -20V, VOUT = 0V LT1121-3.3 LT1121-5 LT1121 (Note 5) VOUT = 3.3V, VIN = 0V VOUT = 5V, VIN = 0V VOUT = 3.8V, VIN = 0V
500 1.0 25 25 25
mA mA A A A
16 16 16
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.
Note 2: The shutdown pin input voltage rating is required for a low impedance source. Internal protection devices connected to the shutdown pin will turn on and clamp the pin to approximately 7V or - 0.6V. This range allows the use of 5V logic devices to drive the pin directly. For high
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LT1121/LT1121-3.3/LT1121-5
ELECTRICAL CHARACTERISTICS
impedance sources or logic running on supply voltages greater than 5.5V, the maximum current driven into the shutdown pin must be limited to less than 20mA. Note 3: For junction temperatures greater than 110C, a minimum load of 1mA is recommended. For TJ > 110C and IOUT < 1mA, output voltage may increase by 1%. Note 4: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range must be limited. When operating at maximum output current the input voltage range must be limited. Note 5: The LT1121 (adjustable version) is tested and specified with the adjust pin connected to the output pin. Note 6: Dropout voltage is the minimum input/output voltage required to maintain regulation at the specified output current. In dropout the output voltage will be equal to: (VIN - VDROPOUT). Note 7: Ground pin current is tested with VIN = VOUT (nominal) and a current source load. This means that the device is tested while operating in its dropout region. This is the worst case ground pin current. The ground pin current will decrease slightly at higher input voltages. Note 8: Adjust pin bias current flows into the adjust pin. Note 9: Shutdown pin current at VSHDN = 0V flows out of the shutdown pin. Note 10: Quiescent current in shutdown is equal to the sum total of the shutdown pin current (6A) and the ground pin current (9A). Note 11: Reverse output current is tested with the input pin grounded and the output pin forced to the rated output voltage. This current flows into the output pin and out of the ground pin.
TYPICAL PERFOR A CE CHARACTERISTICS
Guaranteed Dropout Voltage
0.7 0.6
DROPOUT VOLTAGE (V)
QUIESCENT CURRENT (A)
TJ 125C
DROPOUT VOLTAGE (V)
0.5 0.4 0.3 0.2 0.1 = TEST POINTS 0 0 20 40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
1121 G27
TJ 25C
LT1121-3.3 Quiescent Current
120 100
QUIESCENT CURRENT (A) QUIESCENT CURRENT (A)
80 VSHDN = OPEN 60 40 20 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = 0V
80 VSHDN = OPEN 60 40 20 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = 0V
QUIESCENT CURRENT (A)
4
UW
TJ = 25C RLOAD =
1121 G04
Dropout Voltage
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -50 ILOAD = 50mA ILOAD = 1mA ILLOAD = 100mA ILOAD = 150mA 50
Quiescent Current
VIN = 6V RLOAD = VSHDN = OPEN 30
40
20
VSHDN = 0V
10
-25
50 25 0 75 TEMPERATURE (C)
100
125
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1121 G14
1121 G11
LT1121-5 Quiescent Current
120 100 TJ = 25C RLOAD = 120 100 80
LT1121 Quiescent Current
TJ = 25C RLOAD = VOUT = VADJ
VSHDN = OPEN 60 40 20 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = 0V
1121 G02
1121 G03
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LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFOR A CE CHARACTERISTICS
LT1121-3.3 Output Voltage
3.38 IOUT = 1mA 3.36
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
ADJ PIN VOLTAGE (V)
3.34 3.32 3.30 3.28 3.26 3.24 3.22 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
LT1121-3.3 Ground Pin Current
800 700 TJ = 25C 800 700
GROUND PIN CURRENT (A)
GROUND PIN CURRENT (A)
600 500 400 300
600 500 400 300
GROUND PIN CURRENT (A)
RLOAD = 130 ILOAD = 25mA*
RLOAD = 330 ILOAD = 10mA* *FOR VOUT = 3.3V
200 100 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 RLOAD = 3.3k ILOAD = 1mA*
LT1121-3.3 Ground Pin Current
10 9 TJ = 25C
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (mA)
7 6 5 4 3 2 1 0 0 1 2
RLOAD = 22 ILOAD = 150mA* RLOAD = 33 ILOAD = 100mA*
7 6 5 4 3 2 1 0
RLOAD = 33 ILOAD = 150mA* RLOAD = 50 ILOAD = 100mA*
GROUND PIN CURRENT (mA)
8
RLOAD = 66 ILOAD = 50mA* *FOR VOUT = 3.3V 34567 INPUT VOLTAGE (V) 8 9 10
UW
1121 G22
LT1121-5 Output Voltage
5.08 5.06 5.04 5.02 5.00 4.98 4.96 4.94 4.92 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 3.83 IOUT = 1mA 3.81 3.79 3.77 3.75 3.73 3.71 3.69
LT1121 Adjust Pin Voltage
IOUT = 1mA
3.67 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
1121 G23
1121 G24
LT1121-5 Ground Pin Current
TJ = 25C RLOAD = 200 ILOAD = 25mA* 800
LT1121 Ground Pin Current
TJ = 25C 700 VOUT = VADJ 600 500 400 300 *FOR VOUT = 3.75V 200 100 0 10 0 1 2 RLOAD = 3.8k ILOAD = 1mA* RLOAD = 380 ILOAD = 10mA* RLOAD = 150 ILOAD = 25mA*
RLOAD = 500 ILOAD = 10mA* *FOR VOUT = 5V
200 100 0 0 1 2
RLOAD = 5k ILOAD = 1mA*
34567 INPUT VOLTAGE (V)
8
9
34567 INPUT VOLTAGE (V)
8
9
10
1121 G10
1121 G06
1121 G08
LT1121-5 Ground Pin Current
10 9 8 TJ = 25C 10
LT1121 Ground Pin Current
TJ = 25C 9 VOUT = VADJ 8 7 6 5 4 3 2 1 8 9 10 0 0 1 2 RLOAD = 75 ILOAD = 50mA* *FOR VOUT = 3.75V 34567 INPUT VOLTAGE (V) 8 9 10 RLOAD = 25 ILOAD = 150mA* RLOAD = 38 ILOAD = 100mA*
RLOAD = 100 ILOAD = 50mA* *FOR VOUT = 5V 0 1 2 34567 INPUT VOLTAGE (V)
1121 G09
1121 G05
1121 G07
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LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFOR A CE CHARACTERISTICS
Ground Pin Current
14 VIN = 3.3V (LT1121-3.3) VIN = 5V (LT1121-5) 12 V = 3.75V (LT1121) IN DEVICE IS OPERATING 10 IN DROPOUT 8 6 4 2 0 0 20 40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
1121 G29
GROUND PIN CURRENT (mA)
SHUTDOWN THRESHOLD (V)
SHUTDOWN THRESHOLD (V)
TJ = 125C TJ = 25C TJ = -55C
Shutdown Pin Current
10 9
SHUTDOWN PIN CURRENT (A)
VSHDN = 0V
SHUTDOWN PIN INPUT CURRENT (mA)
8 7 6 5 4 3 2 1 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
20
ADJUST PIN BIAS CURRENT (nA)
Reverse Output Current
30 VIN = 0V VOUT = 5V (LT1121-5) 25 VOUT = 3.3V (LT1121-3.3) VOUT = 3.8V (LT1121) 20 15 10 5 0 -50
400 350
SHORT-CIRCUIT CURRENT (mA)
OUTPUT PIN CURRENT (A)
250 200 150 100 50 0
CURRENT LIMIT (mA)
-25
50 25 0 75 TEMPERATURE (C)
6
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1121 G15
Shutdown Pin Threshold (On-to-Off)
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 ILOAD = 1mA 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Shutdown Pin Threshold (Off-to-On)
ILOAD = 150mA
ILOAD = 1mA
0 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
1121 G16
1121 G17
Shutdown Pin Input Current
25
LT1121 Adjust Pin Bias Current
400 350 300 250 200 150 100 50 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
15
10
5
0 0 1 7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V) 9
1121 G28
1121 G25
Current Limit
VOUT = 0V
Current Limit
400 VIN = 7V 350 VOUT = 0V 300 250 200 150 100 50
300
100
125
0
1
4 3 2 5 INPUT VOLTAGE (V)
6
7
1121 G20
0 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
1121 G13
1121 G19
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LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFOR A CE CHARACTERISTICS
Reverse Output Current
100 TJ = 25C 90 VIN = 0V CURRENT FLOWS 80 INTO OUTPUT PIN 70 60 50 40 30 20 10 0 0 1 2 LT1121-5
52 50 -50 64 62
OUTPUT PIN CURRENT (A)
RIPPLE REJECTION (dB)
RIPPLE REJECTION (dB)
LT1121 (VOUT = VADJ)
LT1121-3.3
345678 OUTPUT VOLTAGE (V)
Load Regulation
0 -5
LOAD REGULATION (mV)
ILOAD = 1mA TO 150mA
OUTPUT VOLTAGE DEVIATION (V)
-10 -15 -20 -25
LT1121*
LT1121-3.3
0 -0.1 -0.2
OUTPUT VOLTAGE DEVIATION (V)
LOAD CURRENT (mA)
-30 -35 * ADJ PIN TIED TO OUTPUT PIN -25 50 25 0 75 TEMPERATURE (C)
LT1121-5
LOAD CURRENT (mA)
-40 -50
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1121 G01
Ripple Rejection
VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz IOUT = 100mA
100
Ripple Rejection
IOUT = 100mA 90 VIN = 6V + 50mVRMS RIPPLE 80 70 60 50 40 30 20 10 0 COUT = 1F SOLID TANTALUM COUT = 47F SOLID TANTALUM
60 58 56 54
10
-25
50 25 0 75 TEMPERATURE (C)
100
125
10
100
1k 10k FREQUENCY (Hz)
100k
1M
1121 G26
1121 G18
LT1121-5 Load Transient Response
VIN = 6V 0.2 CIN = 0.1F = 1F C 0.1 OUT
LT1121-5 Load Transient Response
VIN = 6V 0.2 CIN = 0.1F COUT = 3.3F 0.1 0 -0.1 -0.2
150 100 50 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms)
1121 G31
150 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms)
1121 G30
100
125
1121 G21
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LT1121/LT1121-3.3/LT1121-5
PI FU CTIO S
Input Pin: Power is supplied to the device through the input pin. The input pin should be bypassed to ground if the device is more than six inches away from the main input filter capacitor. In general the output impedance of a battery rises with frequency so it is usually adviseable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 0.1F to 1F is sufficient. The LT1121 is designed to withstand reverse voltages on the input pin with respect to both ground and the output pin. In the case of a reversed input, which can happen if a battery is plugged in backwards, the LT1121 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1121 and no reverse voltage will appear at the load. The device will protect both itself and the load. Output Pin: The output pin supplies power to the load. An output capacitor is required to prevent oscillations. See the Applications Information section for recommended value of output capacitance and information on reverse output characteristics. Shutdown Pin: This pin is used to put the device into shutdown. In shutdown the output of the device is turned off. This pin is active low. The device will be shut down if the shutdown pin is pulled low. The shutdown pin current with the pin pulled to ground will be 6A. The shutdown pin is internally clamped to 7V and - 0.6V (one VBE). This allows the shutdown pin to be driven directly by 5V logic or by open collector logic with a pull-up resistor. The pullup resistor is only required to supply the leakage current of the open collector gate, normally several microamperes. Pull-up current must be limited to a maximum of 20mA. A curve of shutdown pin input current as a function of voltage appears in the Typical Performance Characteristics. If the shutdown pin is not used it can be left open circuit. The device will be active, output on, if the shutdown pin is not connected. Adjust Pin: For the adjustable LT1121, the adjust pin is the input to the error amplifier. This pin is internally clamped to 6V and - 0.6V (one VBE). It has a bias current of 150nA which flows into the pin. See Bias Current curve in the Typical Performance Characteristics. The adjust pin reference voltage is 3.75V referenced to ground. The output voltage range that can be produced by this device is 3.75V to 30V.
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LT1121/LT1121-3.3/LT1121-5
APPLICATIO S I FOR ATIO
The LT1121 is a micropower low dropout regulator with shutdown, capable of supplying up to 150mA of output current at a dropout voltage of 0.4V. The device operates with very low quiescent current (30A). In shutdown the quiescent current drops to only 16A. In addition to the low quiescent current the LT1121 incorporates several protection features which make it ideal for use in batterypowered systems. The device is protected against both reverse input voltages and reverse output voltages. In battery backup applications where the output can be held up by a backup battery when the input is pulled to ground, the LT1121 acts like it has a diode in series with its output and prevents reverse current flow. Adjustable Operation The adjustable version of the LT1121 has an output voltage range of 3.75V to 30V. The output voltage is set by the ratio of two external resistors as shown in Figure 1. The device servos the output voltage to maintain the voltage at the adjust pin at 3.75V. The current in R1 is then equal to 3.75V/R1. The current in R2 is equal to the sum of the current in R1 and the adjust pin bias current. The adjust pin bias current, 150nA at 25C, flows through R2 into the adjust pin. The output voltage can be calculated according to the formula in Figure 1. The value of R1 should be less than 400k to minimize errors in the output voltage caused by the adjust pin bias current. Note that in shutdown the output is turned off and the divider current will be zero. Curves of Adjust Pin Voltage vs Temperature and Adjust Pin Bias Current vs Temperature appear in the Typical Performance Characteristics. The reference voltage at the adjust pin has a slight positive temperature coefficient of
IN LT1121 SHDN GND ADJ R1
1121 * F01
OUT R2
VOUT
+
VOUT = 3.75V 1 + R2 + IADJ * R2 R1 VADJ = 3.75V IADJ = 150nA AT 25C OUTPUT RANGE = 3.75V TO 30V
(
)
(
)
Figure 1. Adjustable Operation
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approximately 15ppm/C. The adjust pin bias current has a negative temperature coefficient. These effects are small and will tend to cancel each other. The adjustable device is specified with the adjust pin tied to the output pin. This sets the output voltage to 3.75V. Specifications for output voltage greater than 3.75V will be proportional to the ratio of the desired output voltage to 3.75V (VOUT/3.75V). For example: load regulation for an output current change of 1mA to 150mA is -12mV typical at VOUT = 3.75V. At VOUT = 12V, load regulation would be:
12V * -12mV = -38mV 3.75V
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Thermal Considerations Power handling capability will be limited by maximum rated junction temperature (125C). Power dissipated by the device will be made up of two components: 1. Output current multiplied by the input/output voltage differential: IOUT * (VIN - VOUT), and 2. Ground pin current multiplied by the input voltage: IGND * VIN. The ground pin current can be found by examining the Ground Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. The LT1121 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal load conditions the maximum junction temperature rating of 125C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered. Heat sinking, for surface mount devices, is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated through holes can also be used to spread the heat generated by power devices. Tables 1 through 5 list thermal resistances for each package. Measured values of thermal resistance for several different board sizes and copper areas are listed for each package. All measurements were
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LT1121/LT1121-3.3/LT1121-5
APPLICATIO S I FOR ATIO
taken in still air, on 3/32" FR-4 board with 1oz copper. All NC leads were connected to the ground plane.
Table 1. N8 Package*
COPPER AREA TOPSIDE 2500 sq mm 1000 sq mm 225 sq mm 1000 sq mm BACKSIDE 2500 sq. mm 2500 sq. mm 2500 sq. mm 1000 sq. mm THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq. mm 2500 sq. mm 2500 sq. mm 1000 sq. mm 80C/W 80C/W 85C/W 91C/W
* Device is mounted on topside. Leads are through hole and are soldered to both sides of board.
Table 2. S8 Package
COPPER AREA TOPSIDE* BACKSIDE 2500 sq. mm 2500 sq. mm 1000 sq. mm 2500 sq. mm 225 sq. mm 100 sq. mm 2500 sq. mm 1000 sq. mm THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq. mm 2500 sq. mm 2500 sq. mm 1000 sq. mm 120C/W 120C/W 125C/W 131C/W
* Device is mounted on topside.
Table 3. AS8 Package*
COPPER AREA TOPSIDE** BACKSIDE BOARD AREA 2500 sq. mm 2500 sq. mm 2500 sq. mm 2500 sq. mm 60C/W 60C/W 68C/W 74C/W 2500 sq. mm 2500 sq. mm 1000 sq. mm 2500 sq. mm 225 sq. mm 100 sq. mm 2500 sq. mm 2500 sq. mm
* Pins 3, 6, and 7 are ground. ** Device is mounted on topside.
Table 4. SOT-223 Package (Thermal Resistance Junction-to-Tab 20C/W)
COPPER AREA TOPSIDE* BACKSIDE 2500 sq. mm 2500 sq. mm 1000 sq. mm 2500 sq. mm 225 sq. mm 100 sq. mm 1000 sq. mm 2500 sq. mm 2500 sq. mm 0 THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500 sq. mm 50C/W 2500 sq. mm 2500 sq. mm 2500 sq. mm 1000 sq. mm 1000 sq. mm 50C/W 58C/W 64C/W 57C/W 60C/W
1000 sq. mm 1000 sq. mm
* Tab of device attached to topside copper
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Table 5. TO-92 Package
Package alone Package soldered into PC board with plated through holes only Package soldered into PC board with 1/4 sq. inch of copper trace per lead Package soldered into PC board with plated through holes in board, no extra copper trace, and a clip-on type heat sink: Thermalloy type 2224B Aavid type 5754 THERMAL RESISTANCE 220C/W 175C/W 145C/W 160C/W 135C/W
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Calculating Junction Temperature Example: given an output voltage of 3.3V, an input voltage range of 4.5V to 7V, an output current range of 0mA to 100mA, and a maximum ambient temperature of 50C, what will the maximum junction temperature be? Power dissipated by the device will be equal to: IOUT MAX * (VIN MAX - VOUT) + (IGND * VIN) where, IOUT MAX = 100mA VIN MAX = 7V IGND at (IOUT = 100mA, VIN = 7V) = 5mA so, P = 100mA * (7V - 3.3V) + (5mA * 7V) = 0.405W
If we use an SOT-223 package, then the thermal resistance will be in the range of 50C/W to 65C/W depending on copper area. So the junction temperature rise above ambient will be less than or equal to: 0.405W * 60C/W = 24C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50C + 24C = 74C Output Capacitance and Transient Performance The LT1121 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 1F with an ESR of 3 or less. For applications where space is very limited, capacitors as low as 0.33F can be used if combined with a small series resistor. Assuming
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LT1121/LT1121-3.3/LT1121-5
APPLICATIO S I FOR ATIO
that the ESR of the capacitor is low (ceramic) the suggested series resistor is shown in Table 6. The LT1121 is a micropower device and output transient response will be a function of output capacitance. See the Transient Response curves in the Typical Performance Characteristics. Larger values of output capacitance will decrease the peak deviations and provide improved output transient response. Bypass capacitors, used to decouple individual components powered by the LT1121, will increase the effective value of the output capacitor.
Table 6. Suggested Series Resistor Values SUGGESTED SERIES OUTPUT CAPACITANCE RESISTOR 0.33F 2 0.47F 1 0.68F 1 >1F None Needed
Protection Features The LT1121 incorporates several protection features which make it ideal for use in battery-powered circuits. In addition to the normal protection features associated with monolithic regulators, such as current limiting and thermal limiting, the device is protected against reverse input voltages, reverse output voltages, and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature should not exceed 125C. The input of the device will withstand reverse voltages of 30V. Current flow into the device will be limited to less than 1mA (typically less than 100A) and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries that can be plugged in backwards. For fixed voltage versions of the device, the output can be pulled below ground without damaging the device. If the input is open circuit or grounded the output can be pulled below ground by 20V. The output will act like an open circuit, no current will flow out of the pin. If the input is powered by a voltage source, the output will source the
OUTPUT PIN CURRENT (A)
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short-circuit current of the device and will protect itself by thermal limiting. For the adjustable version of the device, the output pin is internally clamped at one diode drop below ground. Reverse current for the adjustable device must be limited to 5mA. In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage may be held up while the input is either pulled to ground, pulled to some intermediate voltage, or is left open circuit. Current flow back into the output will vary depending on the conditions. Many battery-powered circuits incorporate some form of power management. The following information will help optimize battery life. Table 7 summarizes the following information. The reverse output current will follow the curve in Figure 2 when the input pin is pulled to ground. This current flows through the output pin to ground. The state of the shutdown pin will have no effect on output current when the input pin is pulled to ground. In some applications it may be necessary to leave the input to the LT1121 unconnected when the output is held high. This can happen when the LT1121 is powered from a rectified AC source. If the AC source is removed, then the input of the LT1121 is effectively left floating. The reverse output current also follows the curve in Figure 2 if the input pin is left open. The state of the shutdown pin will have no effect on the reverse output current when the input pin is floating.
100 TJ = 25C 90 VIN < VOUT CURRENT FLOWS 80 INTO OUTPUT PIN 70 TO GROUND 60 50 40 30 20 10 0 0 1 2 LT1121-5 LT1121-3.3 LT1121 (VOUT = VADJ) 345678 OUTPUT VOLTAGE (V) 9 10
1121* F02
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Figure 2. Reverse Output Current
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LT1121/LT1121-3.3/LT1121-5
APPLICATIO S I FOR ATIO
When the input of the LT1121 is forced to a voltage below its nominal output voltage and its output is held high, the reverse output current will still follow the curve in Figure 2. This condition can occur if the input of the LT1121 is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or by a second regulator circuit. When the input pin is forced below the output pin or the output pin is pulled above the input pin, the input current will typically drop to less than 2A (see Figure 3). The state of the shutdown pin will have no effect on the reverse output current when the output is pulled above the input.
INPUT CURRENT (A)
Table 7. Fault Conditions
INPUT PIN < VOUT (Nominal) < VOUT (Nominal) Open Open 0.8V 0.8V > 1.5V - 30V < VIN < 30V SHDN PIN Open (Hi) Grounded Open (Hi) Grounded Open (Hi) Grounded Open (Hi) Grounded OUTPUT PIN Forced to VOUT (Nominal) Forced to VOUT (Nominal) Forced to VOUT (Nominal) Forced to VOUT (Nominal) 0V 0V 0V 0V Reverse Output Current 15A (See Figure 2) Input Current 1A (See Figure 3) Reverse Output Current 15A (See Figure 2) Input Current 1A (See Figure 3) Reverse Output Current 15A (See Figure 2) Reverse Output Current 15A (See Figure 2) Output Current = 0 Output Current = 0 Output Current = Short-Circuit Current Output Current = 0
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5 VOUT = 3.3V (LT1121-3.3) VOUT = 5V (LT1121-5) 4 3 2 1 0 0 1 3 2 INPUT VOLTAGE (V) 4 5
1121 F03
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Figure 3. Input Current
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LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTIO
.300 - .325 (7.620 - 8.255)
.008 - .015 (0.203 - 0.381)
(
+.035 .325 -.015 8.255 +0.889 -0.381
)
INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)
NOTE: 1. DIMENSIONS ARE
.050 BSC
8
.245 MIN
.030 .005 TYP
RECOMMENDED SOLDER PAD LAYOUT .010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP
NOTE: 1. DIMENSIONS IN
INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
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N8 Package 8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
.400* (10.160) MAX 8 7 6 5 .255 .015* (6.477 0.381) 1 2 3 4 .130 .005 (3.302 0.127) .045 - .065 (1.143 - 1.651) .065 (1.651) TYP .120 (3.048) .020 MIN (0.508) MIN .018 .003 (0.457 0.076)
N8 1002
.100 (2.54) BSC
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
.045 .005
.189 - .197 (4.801 - 5.004) NOTE 3 7 6 5
.160 .005 .228 - .244 (5.791 - 6.197)
.150 - .157 (3.810 - 3.988) NOTE 3
1
2
3
4
.053 - .069 (1.346 - 1.752)
.004 - .010 (0.101 - 0.254)
.016 - .050 (0.406 - 1.270)
.014 - .019 (0.355 - 0.483) TYP
.050 (1.270) BSC
SO8 0303
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LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTIO
.248 - .264 (6.30 - 6.71) .114 - .124 (2.90 - 3.15) .059 MAX
.264 - .287 (6.70 - 7.30) .130 - .146 (3.30 - 3.71)
.0905 (2.30) BSC
.071 (1.80) MAX
.024 - .033 (0.60 - 0.84) .181 (4.60) BSC
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ST Package 3-Lead Plastic SOT-223
(LTC DWG # 05-08-1630)
.129 MAX .248 BSC .039 MAX .059 MAX .090 BSC .181 MAX .033 - .041 (0.84 - 1.04) RECOMMENDED SOLDER PAD LAYOUT 10 - 16 10 MAX .010 - .014 (0.25 - 0.36) 10 - 16 .012 (0.31) MIN .0008 - .0040 (0.0203 - 0.1016)
ST3 (SOT-233) 0502
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LT1121/LT1121-3.3/LT1121-5
PACKAGE DESCRIPTIO
.060 .005 (1.524 0.127) DIA
.180 .005 (4.572 0.127)
.180 .005 (4.572 0.127)
.500 (12.70) MIN
.050 UNCONTROLLED (1.270) LEAD DIMENSION MAX
.050 (1.27) BSC
.016 .003 (0.406 0.076)
.060 .010 (1.524 0.254)
3
2
1
10 NOM
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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Z Package 3-Lead Plastic TO-92 (Similar to TO-226)
(LTC DWG # 05-08-1410)
.90 (2.286) NOM 5 NOM .015 .002 (0.381 0.051)
Z3 (TO-92) 0801
.098 +.016/-.04 (2.5 +0.4/-0.1) 2 PLCS TO-92 TAPE AND REEL REFER TO TAPE AND REEL SECTION OF LTC DATA BOOK FOR ADDITIONAL INFORMATION
.140 .010 (3.556 0.127)
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LT1121/LT1121-3.3/LT1121-5 RELATED PARTS
PART NUMBER LT1120 LT1129 LT1175 LT1521 LT1529 LT1611 LT1613 LTC1627 LT1682 LT1762 Series LT1763 Series LT1764 Series LT1962 Series LT1963 Series DESCRIPTION 125mA Low Dropout Regulator with 20A IQ 700mA Micropower Low Dropout Regulator 500mA Negative Low Dropout Micropower Regulator 300mA Low Dropout Micropower Regulator with Shutdown 3A Low Dropout Regulator with 50A IQ Inverting 1.4MHz Switching Regulator 1.4MHz Single-Cell Micropower DC/DC Converter High Efficiency Synchronous Step-Down Switching Regulator Doubler Charge Pump with Low Noise Linear Regulator 150mA, Low Noise, LDO Micropower Regulator 500mA, Low Noise, LDO Micropower Regulator 3A Fast Transient Response LDO 300mA, Low Noise, LDO Micropower Regulator 1.5A Fast Transient Response LDO COMMENTS Includes 2.5V Reference and Comparator 50A Quiescent Current 45A IQ, 0.26V Dropout Voltage, SOT-223 Package 15A IQ, Reverse Battery Protection 500mV Dropout Voltage 5V to - 5V at 150mA, Low Output Noise, SOT-23 Package SOT-23 Package, Internally Compensated Burst ModeTM Operation, Monolithic, 100% Duty Cycle Low Output Noise: 60VRMS (100kHz BW) 25A Quiescent Current, 20VRMS Noise 30A Quiescent Current, 20VRMS Noise 300mV Dropout, 40VRMS Noise 30A Quiescent Current, 20VRMS Noise 300mV Dropout, 40VRMS Noise
Burst Mode is a trademark of Linear Technology Corporation.
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 FAX: (408) 434-0507 www.linear-tech.com
LT 0407 REV E * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

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