LT1121/LT1121-3.3/LT1121-5 Micropower Low Dropout Regulators with Shutdown FEATURES
n n n n n n n n n n n n n n
DESCRIPTION
The LT®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 battery-powered systems, the low quiescent current, 30µA operating and 16µA 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 0.33µF on the output while most older devices require between 1µF and 100µF 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 16µA will flow from the output pin to ground.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
0.4V Dropout Voltage 150mA Output Current 30µA 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 16µA Quiescent Current in Shutdown Stable with 0.33µF 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
APPLICATIONS
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Low Current Regulator Regulator for Battery-Powered Systems Post Regulator for Switching Supplies
TYPICAL APPLICATION
5V Battery-Powered Supply with Shutdown
0.5 8 5V 5 IN OUT LT1121-3.3 SHDN GND 3 1 3.3VOUT 150mA 1μF SOLID TANTALUM DROPOUT VOLTAGE (V)
Dropout Voltage
+
0.4
0.3
0.2
VSHDN (PIN 5) OUTPUT 2.8 ON NC ON
0.1 0
LT1121 • TA01
0
20
40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
LT1121 • TA02
1121fg
1
LT1121/LT1121-3.3/LT1121-5 ABSOLUTE MAXIMUM RATINGS
(Note 1)
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
Output Short-Circuit Duration ....................... Indefinite Operating Junction Temperature Range (Note 3) LT1121C-X ............................................ 0°C to 125°C LT1121I-X ........................................ – 40°C to 125°C Storage Temperature Range .................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................... 300°C
PIN CONFIGURATION
TOP VIEW OUT 1 NC/ADJ* 2 GND 3 NC 4 N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150°C, θJA = 120°C/W (N8, S8) TJMAX = 150°C, θJA = 70°C/W (AS8) 8 IN 7 NC** 6 NC** 5 SHDN * 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. FRONT VIEW 3 TAB IS GND 2 1 OUTPUT GND VIN Z PACKAGE 3-LEAD PLASTIC TO-92 TJMAX = 150°C, θJA = 150°C/W IN GND OUT BOTTOM VIEW
ST PACKAGE 3-LEAD PLASTIC SOT-223 TJMAX = 150°C, θJA = 50°C/W
ORDER INFORMATION
LEAD FREE FINISH LT1121CN8#PBF LT1121CN8-3.3#PBF LT1121CN8-5#PBF LT1121IN8#PBF LT1121IN8-3.3#PBF LT1121IN8-5#PBF LT1121CS8#PBF LT1121CS8-3.3#PBF LT1121CS8-5#PBF LT1121HVCS8#PBF LT1121IS8#PBF LT1121IS8-3.3#PBF LT1121IS8-5#PBF LT1121HVIS8#PBF LT1121ACS8#PBF LT1121ACS8-3.3#PBF LT1121ACS8-5#PBF TAPE AND REEL LT1121CN8#TRPBF LT1121CN8-3.3#TRPBF LT1121CN8-5#TRPBF LT1121IN8#TRPBF LT1121IN8-3.3#TRPBF LT1121IN8-5#TRPBF LT1121CS8#TRPBF LT1121CS8-3.3#TRPBF LT1121CS8-5#TRPBF LT1121HVCS8#TRPBF LT1121IS8#TRPBF LT1121IS8-3.3#TRPBF LT1121IS8-5#TRPBF LT1121HVIS8#TRPBF LT1121ACS8#TRPBF LT1121ACS8-3.3#TRPBF LT1121ACS8-5#TRPBF PART MARKING LT1121CN8 LT1121CN8-3.3 LT1121CN8-5 LT1121IN8 LT1121IN8-3.3 LT1121IN8-5 1121 11213 11215 1121HV 1121I 121I3 121I5 121HVI 1121A 1121A3 1121A5 PACKAGE DESCRIPTION 8-Lead Plastic PDIP 8-Lead Plastic PDIP 8-Lead Plastic PDIP 8-Lead Plastic PDIP 8-Lead Plastic PDIP 8-Lead Plastic PDIP 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 TEMPERATURE RANGE 0°C to 125°C 0°C to 125°C 0°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C 0°C to 125°C 0°C to 125°C 0°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C 0°C to 125°C 0°C to 125°C 0°C to 125°C
1121fg
2
LT1121/LT1121-3.3/LT1121-5 ORDER INFORMATION
LEAD FREE FINISH LT1121AHVCS8#PBF LT1121AIS8#PBF LT1121AIS8-3.3#PBF LT1121AIS8-5#PBF LT1121AHVIS8#PBF LT1121CST-3.3#PBF LT1121IST-3.3#PBF LT1121CST-5#PBF LT1121IST-5#PBF LT1121CZ3-3#PBF LT1121IZ3-3#PBF LT1121CZ-5#PBF LT1121IZ-5#PBF TAPE AND REEL LT1121AHVCS8#TRPBF LT1121AIS8#TRPBF LT1121AIS8-3.3#TRPBF LT1121AIS8-5#TRPBF LT1121AHVIS8#TRPBF LT1121CST-3.3#TRPBF LT1121IST-3.3#TRPBF LT1121CST-5#TRPBF LT1121IST-5#TRPBF LT1121CZ3-3#TRPBF LT1121IZ3-3#TRPBF LT1121CZ-5#TRPBF LT1121IZ-5#TRPBF PART MARKING 121AHV 121AI 121AI3 121AI5 21AHVI 11213 121I3 11215 1121I5 LT1121CZ3-3 LT1121IZ3-3 LT1121CZ-5 LT1121IZ-5 PACKAGE DESCRIPTION 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 8-Lead Plastic S0 3-Lead Plastic SOT-223 3-Lead Plastic SOT-223 3-Lead Plastic SOT-223 3-Lead Plastic SOT-223 3-Lead Plastic TO-92 3-Lead Plastic TO-92 3-Lead Plastic TO-92 3-Lead Plastic TO-92 TEMPERATURE RANGE 0°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C –40°C to 125°C 0°C to 125°C –40°C to 125°C 0°C to 125°C –40°C to 125°C 0°C to 125°C –40°C to 125°C 0°C to 125°C –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on nonstandard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER Regulated Output Voltage (Note 4) CONDITIONS LT1121-3.3 LT1121-5 LT1121 (Note 5) Line Regulation
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
MIN VIN = 3.8V, IOUT = 1mA, TJ = 25ºC 4.3V < VIN < 20V, 1mA < IOUT < 150mA VIN = 5.5V, IOUT = 1mA, TJ = 25ºC 6V < VIN < 20V, 1mA < IOUT < 150mA VIN = 4.3V, IOUT = 1mA, TJ = 25ºC 4.8V < VIN < 20V, 1mA < IOUT < 150mA
l l l l l l l l l l
TYP 3.3 3.3 5 5 3.75 3.75 1.5 1.5 1.5 –12 –20 –17 –28 –12 –18 0.13 0.3
MAX 3.35 3.4 5.075 5.15 3.805 3.86 10 10 10 –25 –40 –35 –50 –25 –40 0.16 0.25 0.35 0.5 0.45 0.6 0.55 0.7
UNITS V V V V V V mV mV mV mV mV mV mV mV mV V V V V V V V V
1121fg
3.25 3.2 4.925 4.85 3.695 3.64
Load Regulation
LT1121-3.3 ΔVIN = 4.8V TO 20V, IOUT = 1mA LT1121-5 ΔVIN = 5.5V TO 20V, IOUT = 1mA LT1121 (Note 5) ΔVIN = 4.3V TO 20V, IOUT = 1mA LT1121-3.3 ΔILOAD = 1mA to 150mA, TJ = 25ºC ΔILOAD = 1mA to 150mA LT1121-5 ΔILOAD = 1mA to 150mA, TJ = 25ºC ΔILOAD = 1mA to 150mA LT1121 (Note 5) ΔILOAD = 1mA to 150mA, TJ = 25ºC ΔILOAD = 1mA to 150mA ILOAD = 1mA, TJ = 25ºC ILOAD = 1mA ILOAD = 50mA, TJ = 25ºC ILOAD = 50mA ILOAD = 100mA, TJ = 25ºC ILOAD = 100mA ILOAD = 150mA, TJ = 25ºC ILOAD = 150mA
Dropout Voltage (Note 6)
l
0.37
l
0.42
l
3
LT1121/LT1121-3.3/LT1121-5 ELECTRICAL CHARACTERISTICS
PARAMETER Ground Pin Current (Note 7) CONDITIONS ILOAD = 0mA ILOAD = 1mA ILOAD = 10mA ILOAD = 50mA ILOAD = 100mA ILOAD = 150mA TJ = 25ºC VOUT = Off to On VOUT = On to Off VSHDN = 0V VIN – VOUT = 1V (Avg), VRIPPLE = 0.5VP-P , fRIPPLE = 120Hz, ILOAD = 0.1A VIN – VOUT = 7V, TJ = 25ºC VIN = –20V, VOUT = 0V LT1121-3.3 VOUT = 3.3V, VIN = 0V LT1121-5 VOUT = 5V, VIN = 0V LT1121 (Note 5) VOUT = 3.8V, VIN = 0V
l l l l l l l l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
MIN TYP 30 90 350 1.5 4 7 150 0.25 1.2 0.75 6 16 50 58 200 16 16 16 500 1 25 25 25 MAX 50 120 500 2.5 7 14 300 2.8 10 22 UNITS µA µA µA mA mA mA nA V V µA µA dB mA mA µA µA µA
Adjust Pin Bias Current (Notes 5, 8) Shutdown Threshold Shutdown Pin Current (Note 9) Ripple Rejection Current Limit Input Reverse Leakage Current Reverse Output Current (Note 11)
Quiescent Current in Shutdown (Note 10) VIN = 6V, VSHDN = 0V
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 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 110°C, a minimum load of 1mA is recommended. For TJ > 110°C 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 (6µA) and the ground pin current (9µA). 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.
1121fg
4
LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.7 0.6 DROPOUT VOLTAGE (V) 0.5 0.4 0.3 0.2 0.1 0 = TEST POINTS 0 20 40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
1121 G01
Dropout Voltage
0.7 50 ILOAD = 150mA QUIESCENT CURRENT (μA) ILOAD = 100mA 0.6 DROPOUT VOLTAGE (V) 0.5 0.4 0.3 0.2 0.1 0 –50 50 25 0 75 TEMPERATURE (°C) 100 125 ILOAD = 50mA ILOAD = 1mA
Quiescent Current
VIN = 6V RLOAD = ∞ VSHDN = OPEN 30
TJ ≤ 125°C
40
TJ ≤ 25°C
20
VSHDN = 0V
10
–25
0 –50
–25
50 25 0 75 TEMPERATURE (°C)
100
125
1121 G02
1121 G03
LT1121-3.3 Quiescent Current
120 100 QUIESCENT CURRENT (μA) 80 60 40 20 0 VSHDN = 0V VSHDN = OPEN TJ = 25°C RLOAD = ∞ QUIESCENT CURRENT (μA) 120 100 80
LT1121-5 Quiescent Current
TJ = 25°C RLOAD = ∞ QUIESCENT CURRENT (μA) 120 100 80
LT1121 Quiescent Current
TJ = 25°C RLOAD = ∞ VOUT = VADJ
VSHDN = OPEN 60 40 20 0 VSHDN = 0V
VSHDN = OPEN 60 40 20 0 VSHDN = 0V
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
1121 G04
1121 G05
1121 G06
LT1121-3.3 Output Voltage
3.38 3.36 OUTPUT VOLTAGE (V) 3.34 3.32 3.30 3.28 3.26 3.24 3.22 –50 –25 50 0 75 25 TEMPERATURE (°C) 100 125 IOUT = 1mA 5.08 5.06 OUTPUT VOLTAGE (V)
LT1121-5 Output Voltage
IOUT = 1mA 3.83 3.81 ADJ PIN VOLTAGE (V) 3.79 3.77 3.75 3.73 3.71 3.69 –25 50 0 75 25 TEMPERATURE (°C) 100 125
LT1121 Adjust Pin Voltage
IOUT = 1mA
5.04 5.02 5.00 4.98 4.96 4.94 4.92 –50
3.67 –50
–25
50 0 75 25 TEMPERATURE (°C)
100
125
1121 G07
1121 G08
1121 G09
1121fg
5
LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFORMANCE CHARACTERISTICS
LT1121-3.3 Ground Pin Current
800 700 GROUND PIN CURRENT (μA) 600 500 400 300 200 100 0 0 1 2 RLOAD = 330Ω ILOAD = 10mA* *FOR VOUT = 3.3V RLOAD = 3.3k ILOAD = 1mA* 34567 INPUT VOLTAGE (V) 8 9 10 TJ = 25°C GROUND PIN CURRENT (μA) RLOAD = 130Ω ILOAD = 25mA* 800 700 600 500 400 300 200 100 0 0 1 2 RLOAD = 500Ω ILOAD = 10mA* *FOR VOUT = 5V RLOAD = 5k ILOAD = 1mA* 34567 INPUT VOLTAGE (V) 8 9 10
LT1121-5 Ground Pin Current
TJ = 25°C GROUND PIN CURRENT (μA) RLOAD = 200Ω ILOAD = 25mA* 800
LT1121 Ground Pin Current
TJ = 25°C 700 VOUT = VADJ 600 500 400 300 200 100 0 0 1 2 RLOAD = 380Ω ILOAD = 10mA* *FOR VOUT = 3.75V RLOAD = 3.8k ILOAD = 1mA* 34567 INPUT VOLTAGE (V) 8 9 10 RLOAD = 150Ω ILOAD = 25mA*
1121 G10
1121 G11
1121 G12
LT1121-3.3 Ground Pin Current
10 9 GROUND PIN CURRENT (mA) 8 7 6 5 4 3 2 1 0 0 1 2 RLOAD = 66Ω ILOAD = 50mA* *FOR VOUT = 3.3V 34567 INPUT VOLTAGE (V) 8 9 10 TJ = 25°C GROUND PIN CURRENT (mA) RLOAD = 22Ω ILOAD = 150mA* RLOAD = 33Ω ILOAD = 100mA* 10 9 8 7 6 5 4 3 2 1 0
LT1121-5 Ground Pin Current
TJ = 25°C GROUND PIN CURRENT (mA) 10
LT1121 Ground Pin Current
TJ = 25°C 9 VOUT = VADJ 8 7 6 5 4 3 2 1 8 9 10 0 0 1 2 RLOAD = 25Ω ILOAD = 150mA* RLOAD = 38Ω ILOAD = 100mA* RLOAD = 75Ω ILOAD = 50mA* *FOR VOUT = 3.75V 34567 INPUT VOLTAGE (V) 8 9 10
RLOAD = 33Ω ILOAD = 150mA* RLOAD = 50Ω ILOAD = 100mA* RLOAD = 100Ω ILOAD = 50mA* *FOR VOUT = 5V 0 1 2 34567 INPUT VOLTAGE (V)
1121 G13
1121 G14
1121 G15
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 40 60 80 100 120 140 160 OUTPUT CURRENT (mA)
1121 G16
Shutdown Pin Threshold (On-to-Off)
2.0 1.8 SHUTDOWN THRESHOLD (V) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ILOAD = 1mA SHUTDOWN THRESHOLD (V) 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 –25 50 25 0 75 TEMPERATURE (°C) 100 125
Shutdown Pin Threshold (Off-to-On)
GROUND PIN CURRENT (mA)
ILOAD = 150mA
TJ = 125°C TJ = 25°C TJ = –55°C
ILOAD = 1mA
20
0 –50
0 –50
–25
50 25 0 75 TEMPERATURE (°C)
100
125
1121 G17
1121 G18
1121fg
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LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Current
10 9 SHUTDOWN PIN CURRENT (μA) 8 7 6 5 4 3 2 1 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 SHUTDOWN PIN INPUT CURRENT (mA) VSHDN = 0V 25 20 ADJUST PIN BIAS CURRENT (nA)
Shutdown Pin Input Current
400 350 300 250 200 150 100 50
LT1121 Adjust Pin Bias Current
15
10 5 0
0
1
7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V)
9
0 –50
–25
50 0 75 25 TEMPERATURE (°C)
100
125
1121 G19
1121 G20
1121 G21
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 SHORT-CIRCUIT CURRENT (mA) 350
Current Limit
VOUT = 0V 400
Current Limit
VIN = 7V 350 VOUT = 0V CURRENT LIMIT (mA) 300 250 200 150 100 50
OUTPUT PIN CURRENT (μA)
300 250 200 150 100 50 0 0 1 4 2 5 3 INPUT VOLTAGE (V) 6 7
1121 G23
–25
50 25 0 75 TEMPERATURE (°C)
100
125
0 –50
–25
50 0 75 25 TEMPERATURE (°C)
100
125
1121 G22
1121 G24
Reverse Output Current
100 TJ = 25°C 90 VIN = 0V CURRENT FLOWS 80 INTO OUTPUT PIN 70 60 50 40 30 20 10 0 0 1 2 LT1121 (VOUT = VADJ) LT1121-3.3 64
Ripple Rejection
VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz 62 IOUT = 100mA RIPPLE REJECTION (dB) RIPPLE REJECTION (dB) 60 58 56 54 52 9 10 50 –50 50 25 0 75 TEMPERATURE (°C) 100 125 100
Ripple Rejection
IOUT = 100mA 90 VIN = 6V + 50mVRMS RIPPLE 80 70 60 50 40 30 20 10 COUT = 1μF SOLID TANTALUM COUT = 47μF SOLID TANTALUM
OUTPUT PIN CURRENT (μA)
LT1121-5 345678 OUTPUT VOLTAGE (V)
–25
0
10
100
1k 10k FREQUENCY (Hz)
100k
1M
1121 G27
1121 G25
1121 G26
1121fg
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LT1121/LT1121-3.3/LT1121-5 TYPICAL PERFORMANCE CHARACTERISTICS
Load Regulation
0 –5 LOAD REGULATION (mV) –10 –15 –20 –25 –30 –35 * ADJ PIN TIED TO OUTPUT PIN –25 50 0 75 25 TEMPERATURE (°C) 100 125 150 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 TIME (ms)
1121 G29
LT1121-5 Load Transient Response
OUTPUT VOLTAGE DEVIATION (V) OUTPUT VOLTAGE DEVIATION (V) VIN = 6V 0.2 CIN = 0.1μF = 1μF C 0.1 OUT 0 –0.1 –0.2
LT1121-5 Load Transient Response
VIN = 6V 0.2 CIN = 0.1μF COUT = 3.3μF 0.1 0 –0.1 –0.2
ΔILOAD = 1mA TO 150mA LT1121* LT1121-3.3
LOAD CURRENT (mA)
LT1121-5
LOAD CURRENT (mA)
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 G30
–40 –50
1121 G28
PIN FUNCTIONS
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 0.1µF to 1µF 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 6µA. 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 pull-up 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.
1121fg
8
LT1121/LT1121-3.3/LT1121-5 APPLICATIONS INFORMATION
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 (30µA). In shutdown the quiescent current drops to only 16µA. 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 25°C, 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
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 ⎞ ⎜ 3.75V ⎟ • ( –12mV ) = ( –38mV ) ⎝ ⎠ Thermal Considerations Power handling capability will be limited by maximum rated junction temperature (125°C). 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 125°C 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 taken in still air, on 3/32" FR-4 board with 1oz copper. All
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OUT R2
VOUT
+
VOUT = 3.75V 1 + R2 + IADJ • R2 R1 VADJ = 3.75V IADJ = 150nA AT 25°C OUTPUT RANGE = 3.75V TO 30V
(
)
(
)
Figure 1. Adjustable Operation
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LT1121/LT1121-3.3/LT1121-5 APPLICATIONS INFORMATION
NC leads were connected to the ground plane.
Table 1. N8 Package*
COPPER AREA TOPSIDE BACKSIDE BOARD AREA 2500 sq mm 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 225 sq mm 2500 sq mm 1000 sq mm 1000 sq mm THERMAL RESISTANCE JUNCTION TO AMBIENT 80ºC/W 80ºC/W 85ºC/W 91ºC/W
Table 5. TO-92 Package THERMAL RESISTANCE
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 220ºC/W 175ºC/W 145ºC/W 160ºC/W
135ºC/W
* Device is mounted on topside. Leads are through hole and are soldered to both sides of board.
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 50°C, 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
Table 2. S8 Package
COPPER AREA TOPSIDE* BACKSIDE BOARD AREA 2500 sq mm 2500 sq mm 2500 sq mm 1000 sq mm 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 JUNCTION TO AMBIENT 120ºC/W 120ºC/W 125ºC/W 131ºC/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 2500 sq mm 2500 sq mm 1000 sq mm 2500 sq mm 225 sq mm 100 sq mm 2500 sq mm 2500 sq mm THERMAL RESISTANCE JUNCTION TO AMBIENT 60ºC/W 60ºC/W 68ºC/W 74ºC/W
If we use an SOT-223 package, then the thermal resistance will be in the range of 50°C/W to 65°C/W depending on copper area. So the junction temperature rise above ambient will be less than or equal to: 0.405W • 60°C/W = 24°C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50°C + 24°C = 74°C Output Capacitance and Transient Performance The LT1121 is designed to be stable with a wide range of output capacitors. The minimum recommended value is 1µF with an ESR of 3Ω or less. For applications where space is very limited, capacitors as low as 0.33µF can be used if combined with a small series resistor. Assuming that the ESR of the capacitor is low (ceramic) the suggested series
1121fg
* Pins 3, 6 and 7 are ground. ** Device is mounted on topside.
Table 4. SOT-223 Package (Thermal Resistance Junction-to-Tab 20ºC/W)
COPPER AREA TOPSIDE* BACKSIDE BOARD AREA 2500 sq mm 2500 sq mm 2500 sq mm 2500 sq mm 1000 sq mm 1000 sq mm 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 JUNCTION TO AMBIENT 50ºC/W 50ºC/W 58ºC/W 64ºC/W 57ºC/W 60ºC/W
1000 sq mm 2500 sq mm
* Tab of device attached to topside copper.
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LT1121/LT1121-3.3/LT1121-5 APPLICATIONS INFORMATION
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
OUTPUT CAPACITANCE 0.33µF 0.47µF 0.68µF >1µF SUGGESTED SERIES RESISTOR 2Ω 1Ω 1Ω None Needed
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 = 25°C 90 VIN < VOUT CURRENT FLOWS 80 INTO OUTPUT PIN 70 TO GROUND 60 50 40 30 20 10 0 0 1 2 LT1121 (VOUT = VADJ) LT1121-3.3
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 125°C. 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 100µA) 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 (μA)
LT1121-5 345678 OUTPUT VOLTAGE (V) 9 10
1121• F02
Figure 2. Reverse Output Current
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LT1121/LT1121-3.3/LT1121-5 APPLICATIONS INFORMATION
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 2µA (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.
5 VOUT = 3.3V (LT1121-3.3) VOUT = 5V (LT1121-5) 4 INPUT CURRENT (μA)
3
2
1
0
0
1
3 2 INPUT VOLTAGE (V)
4
5
1121 F03
Figure 3. Input Current Table 7. Fault Conditions
INPUT PIN