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LT1521/LT1521-3 LT1521-3.3/LT1521-5 300mA Low Dropout Regulators with Micropower Quiescent Current and Shutdown
FEATURES
s s s s s s s s s s s
DESCRIPTION
The LT (R)1521/LT1521-3/LT1521-3.3/LT1521-5 are low dropout regulators with micropower quiescent current and shutdown. These devices are capable of supplying 300mA of output current with a dropout voltage of 0.5V. Designed for use in battery-powered systems, the low quiescent current, 12A operating and 6A 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 LT1521/LT1521-3/LT1521-3.3/ LT1521-5 include the ability to operate with very small output capacitors. They are stable with only 1.5F on the output while most older devices require between 10F and 100F for stability. Small ceramic capacitors can be used, enhancing manufacturability. Also, the input may be connected to voltages lower than the output voltage, including negative voltages, without reverse current flow from output to input. This makes the LT1521 series ideal for backup power situations where the output is held high and the input is low or reversed. Under these conditions only 5A will flow from the output pin to ground.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Dropout Voltage: 0.5V Output Current: 300mA Quiescent Current: 12A No Protection Diodes Needed Adjustable Output from 3.8V to 20V Fixed Output Voltages: 3V, 3.3V, 5V Controlled Quiescent Current in Dropout Shutdown IQ = 6A Reverse Battery Protection No Reverse Current Thermal Limiting
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
8 IN LT1521-5 5 SHDN GND 3 SENSE 2 OUT 1 5V 300mA
0.6 0.5
DROPOUT VOLTAGE (V)
+
6V 1F 1.5F
0.4 0.3 0.2 0.1
VSHDN (PIN 5) OUTPUT <0.25 OFF >2.80 ON NC ON
LT1521 * TA01
0
0
50
U
U
U
Dropout Voltage
100 150 200 250 OUTPUT CURRENT (mA)
300
LT1521 * TA02
1
LT1521/LT1521-3 LT1521-3.3/LT1521-5
ABSOLUTE MAXIMUM RATINGS
Input Voltage ...................................................... 20V* Output Pin Reverse Current .................................. 10mA Adjust Pin Current ................................................ 10mA Shutdown Pin Input Voltage (Note 1) .......... 6.5V, - 0.6V Shutdown Pin Input Current (Note 1) ..................... 5mA Output Short-Circuit Duration .......................... Indefinite
PACKAGE/ORDER INFORMATION
TOP VIEW
TOP VIEW OUT SENSE/ADJ* NC GND 1 2 3 4 8 7 6 5 IN NC NC SHDN
OUT 1 SENSE/ADJ* 2 GND 3 NC 4
MS8 PACKAGE 8-LEAD PLASTIC MSOP *PIN 2 = SENSE FOR LT1521-3/ LT1521-3.3/LT1521-5 PIN 2 = ADJ FOR LT1521 TJMAX = 125C, JA = 125C/ W
*PIN 2 = SENSE FOR LT1521-3/LT1521-3.3/LT1521-5 = ADJ FOR LT1521
TJMAX = 125C, JA = 70C/ W SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER LT1521CMS8 LT1521CMS8-3 LT1521CMS8-3.3 LT1521CMS8-5
ORDER PART NUMBER LT1521CS8 LT1521CS8-3 LT1521CS8-3.3 LT1521CS8-5 LT1521IS8 LT1521IS8-3 LT1521IS8-3.3 LT1521IS8-5 S8 PART MARKING 1521 15213 152133 15215 1521I 1521I3 1521I33 1521I5
MS8 PART MARKING LTEZ LTFB LTDU LTFA
Consult factory for Military grade parts.
2
U
U
W
WW U
W
(Note 1)
Storage Temperature Range ................. - 65C to 150C Operating Junction Temperature Range (Note 2) Commercial ........................................... 0C to 125C Industrial ......................................... - 40C to 125C Lead Temperature (Soldering, 10 sec).................. 300C
*For applications requiring input voltage ratings greater than 20V, contact the factory.
FRONT VIEW
8 7 6 5 IN GND GND SHDN
1 TAB IS GND 2 3
OUT GND IN
S8 PACKAGE 8-LEAD PLASTIC SO
ST PACKAGE 3-LEAD PLASTIC SOT-223
TJMAX = 125 C, JA = 50C/ W SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER LT1521CST-3 LT1521CST-3.3 LT1521CST-5 LT1521IST-3 LT1521IST-3.3 LT1521IST-5
ST PART MARKING 15213 152133 15215 1521I3 1521I33 1521I5
LT1521/LT1521-3 LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER Regulated Output Voltage (Note 4) CONDITIONS LT1521-3 VIN = 3.5V, IOUT = 1mA, TJ = 25C 4V < VIN < 20V, 1mA < IOUT < 300mA LT1521-3.3 VIN = 3.8V, IOUT = 1mA, TJ = 25C 4.3V < VIN < 20V, 1mA < IOUT < 300mA LT1521-5 VIN = 5.5V, IOUT = 1mA, TJ = 25C 6V < VIN < 20V, 1mA < IOUT < 300mA LT1521 (Note 5) VIN = 4.3V, IOUT = 1mA, TJ = 25C 4.8V < VIN < 20V, 1mA < IOUT < 300mA LT1521-3 VIN = 4.5 to 20V, IOUT = 1mA LT1521-3.3 VIN = 4.8 to 20V, IOUT = 1mA LT1521-5 VIN = 5.5 to 20V, IOUT = 1mA LT1521 (Note 5) VIN = 4.3 to 20V, IOUT = 1mA LT1521-3 ILOAD = 1mA to 300mA, TJ 25C LT1521-3.3 ILOAD = 1mA to 300mA, TJ 25C LT1521-5 ILOAD = 1mA to 300mA, TJ 25C LT1521 (Note 5) ILOAD = 1mA to 300mA, TJ 25C LT1521-3 ILOAD = 1mA to 300mA, TJ >25C LT1521-3.3 ILOAD = 1mA to 300mA, TJ > 25C LT1521-5 ILOAD = 1mA to 300mA, TJ > 25C LT1521 (Note 5) ILOAD = 1mA to 300mA, TJ > 25C ILOAD = 1mA, TJ = 25C ILOAD = 1mA ILOAD = 50mA, TJ = 25C ILOAD = 50mA ILOAD = 100mA, TJ = 25C ILOAD = 100mA ILOAD = 150mA, TJ = 25C ILOAD = 150mA ILOAD = 300mA, TJ = 25C ILOAD = 300mA ILOAD = 0mA ILOAD = 1mA ILOAD = 10mA ILOAD = 50mA ILOAD = 100mA ILOAD = 150mA ILOAD = 300mA TJ = 25C VOUT = Off to On VOUT = On to Off VSHDN = 0V VIN = VOUT (NOMINAL) + 1V, VSHDN = 0V VIN - VOUT = 1V(Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 150mA VIN - VOUT = 7V, TJ = 25C VIN = VOUT (NOMINAL) + 1.5V, VOUT = - 0.1V
q q q q q q q q
MIN 2.950 2.900 3.250 3.200 4.925 4.850 3.695 3.640
Line Regulation
Load Regulation
Dropout Voltage (Note 6)
TYP 3.000 3.000 3.300 3.300 5.000 5.000 3.750 3.750 1.5 1.5 1.5 1.5 - 20 - 20 - 25 - 20 - 20 - 20 - 25 - 20 130 290
q q
350
q
400
q
500
q q q q q q q q q q q q
Ground Pin Current (Note 7)
Adjust Pin Bias Current (Notes 5, 8) Shutdown Threshold Shutdown Pin Current (Note 9) Quiescent Current in Shutdown (Note 10) Ripple Rejection Current Limit
0.25
50
12 65 300 0.8 1.4 2.2 6.5 50 1.20 0.75 2.0 6 58 400 400
MAX 3.050 3.100 3.350 3.400 5.075 5.150 3.805 3.860 20 20 20 20 - 30 - 30 - 45 - 30 - 55 - 55 - 75 - 55 170 250 350 450 420 550 470 600 600 750 20 100 450 1.5 2.5 4.0 12.0 100 2.80 5.0 12
UNITS V V V V V V V V mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV A A A mA mA mA mA nA V V A A dB mA mA
800
q
320
3
LT1521/LT1521-3 LT1521-3.3/LT1521-5
ELECTRICAL CHARACTERISTICS
PARAMETER Input Reverse Leakage Current Reverse Output Current (Note 11) CONDITIONS VIN = - 20V, VOUT = 0V LT1521-3 VOUT = 3V, VIN < 3V, TJ = 25C LT1521-3.3 VOUT = 3.3V, VIN < 3.3V, TJ = 25C LT1521-5 VOUT = 5V, VIN < 5V, TJ = 25C LT1521 (Note 5) VOUT = 3.8V, VIN < 3.75V, TJ = 25C MIN
q
TYP 5 5 5 5
MAX 1.0 10 10 10 10
UNITS mA A A A A
The q denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 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 5mA. 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 LT1521 (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 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 total sum of the shutdown pin current (2A) and the ground pin current (4A). 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 PERFORMANCE CHARACTERISTICS
Guaranteed Dropout Voltage
0.8 = TEST POINTS 0.7
0.7
DROPOUT VOLTAGE (V)
DROPOUT VOLTAGE (V)
0.6 0.5 0.4 0.3 0.2 0.1 0 0
TJ 125C
0.6 0.5 0.4 0.3 0.2 0.1 0 -50 -25 0
ILOAD = 300mA ILOAD = 150mA ILOAD = 100mA
QUIESCENT CURRENT (A)
TJ 25C
50
200 250 150 OUTPUT CURRENT (mA)
100
4
UW
Dropout Voltage
0.8 15.0 12.5 10.0 7.5 5.0 2.5
Quiescent Current
VSHDN = OPEN
VSHDN = 0V VIN = 6V RL = ILOAD = 0 50 25 75 0 TEMPERATURE (C) 100 125
ILOAD = 50mA ILOAD = 1mA 50 75 25 TEMPERATURE (C) 100 125
300
0 -50 -25
LT1521 * TPC01
LT1521 * TPC02
LT1521 * TPC03
LT1521/LT1521-3 LT1521-3.3/LT1521-5 TYPICAL PERFORMANCE CHARACTERISTICS
LT1521-3 Output Voltage
3.08 3.06
3.38 3.36 IOUT = 1mA
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.04 3.02 3.00 2.98 2.96 2.94 2.92 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125
LT1521 Adjust Pin Voltage
3.83 3.81 ILOAD = 1mA
QUIESCENT CURRENT (A)
50 45 40 35 30 25 20 15 10 5 0
OUTPUT VOLTAGE (V)
3.79 3.77 3.75 3.73 3.71 3.69 3.67 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125
QUIESCENT CURRENT (A)
LT1521-5 Quiescent Current
50 45 TJ = 25C RL =
QUIESCENT CURRENT (A)
GROUND PIN CURRENT (A)
QUIESCENT CURRENT (A)
40 35 30 25 20 15 10 5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = 0V VSHDN = OPEN
UW
LT1521-3.3 Output Voltage
5.08 5.06 5.04 5.02 5.00 4.98 4.96 4.94
-25 0 75 50 25 TEMPERATURE (C) 100 125
LT1521-5 Output Voltage
3.34 3.32 3.30 3.28 3.26 3.24 3.22 -50
4.92 -50 -25
0
50 75 25 TEMPERATURE (C)
100
125
LT1521 * TPC04
LT1521 * TPC05
LT1521 * TPC06
LT1521-3 Quiescent Current
50
TJ = 25C RL =
LT1521-3.3 Quiescent Current
45 40 35 30 25 20 15 10 5
8 9
TJ = 25C RL =
VSHDN = OPEN VSHDN = 0V
0
1
2
34567 INPUT VOLTAGE (V)
0
10
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
LT1521 * TPC07
LT1521 * TPC08
LT1521 * TPC09
LT1521 Quiescent Current
50 45 40 35 30 25 20 15 10 5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 VSHDN = 0V VSHDN = OPEN TJ = 25C RL = 1000 900 800 700 600 500 400 300 200 100 0
LT1521-3 Ground Pin Current
TJ = 25C *FOR VOUT = 3V RLOAD = 60 ILOAD = 50mA* RLOAD = 120 ILOAD = 25mA* RLOAD = 300 ILOAD = 10mA* RLOAD = 3k ILOAD = 1mA* 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
LT1521 * TPC10
LT1521 * TPC11
LT1521 * TPC12
5
LT1521/LT1521-3 LT1521-3.3/LT1521-5 TYPICAL PERFORMANCE CHARACTERISTICS
LT1521-3 Ground Pin Current
8 7 GROUND PIN CURRENT (mA) 6 5 4 3 2 1 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 RLOAD = 30 ILOAD = 100mA* RLOAD = 20 ILOAD = 150mA* RLOAD = 10 ILOAD = 300mA* TJ = 25C *FOR VOUT = 3V 1000 900 TJ = 25C *FOR VOUT = 3.3V RLOAD = 66 ILOAD = 50mA* RLOAD = 132 ILOAD = 25mA* RLOAD = 330 ILOAD = 10mA* RLOAD = 3.3k ILOAD = 1mA* 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (A)
LT1521-5 Ground Pin Current
1000 900 TJ = 25C *FOR VOUT = 5V RLOAD = 100 ILOAD = 50mA* 8 7
GROUND PIN CURRENT (mA)
GROUND PIN CURRENT (A)
GROUND PIN CURRENT (A)
800 700 600 500 400 300 200 100 0 0 1 2
RLOAD = 200 ILOAD = 25mA* RLOAD = 500 ILOAD = 10mA*
RLOAD = 5k ILOAD = 1mA* 34567 INPUT VOLTAGE (V) 8 9 10
LT1521 Ground Pin Current
8 7 GROUND PIN CURRENT (mA) 6 5 4 3 2 1 0 0 1 2 RLOAD = 37.5 ILOAD =100mA* 34567 INPUT VOLTAGE (V) 8 9 10 RLOAD = 25 ILOAD =150mA* TJ = 25C VOUT = VADJ *FOR VOUT = 3.75V RLOAD = 12.5 ILOAD =300mA*
GROUND PIN CURRENT (mA)
8 7 6 5 4 3 2 1 0 0
TJ = 125C
SHUTDOWN PIN THRESHOLD (V)
6
UW
LT1521 * TPC13 LT1521 * TPC16 LT1521 * TPC19
LT1521-3.3 Ground Pin Current
8 7 6 5 4 3 2 1 0
LT1521-3.3 Ground Pin Current
TJ = 25C *FOR VOUT = 3.3V RLOAD = 11 ILOAD = 300mA*
800 700 600 500 400 300 200 100 0
RLOAD = 22 ILOAD = 150mA*
RLOAD = 33 ILOAD = 100mA* 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
LT1521 * TPC14
LT1521 * TPC15
LT1521-5 Ground Pin Current
1000 TJ = 25C *FOR VOUT = 5V RLOAD = 16.7 ILOAD = 300mA* 900 800 700 600 500 400 300 200 100 0 8 9 10
LT1521 Ground Pin Current
TJ = 25C VOUT = VADJ *FOR VOUT = 3.75V RLOAD = 75 ILOAD = 50mA* RLOAD = 150 ILOAD = 25mA* RLOAD = 375 ILOAD = 10mA* RLOAD = 3.8k ILOAD = 1mA* 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
6 5 4 3 2 1 0 0 1 2 RLOAD = 50 ILOAD = 100mA* 34567 INPUT VOLTAGE (V) RLOAD = 33.3 ILOAD = 150mA*
LT1521 * TPC17
LT1521 * TPC18
Ground Pin Current
10 9 VIN = 3V (LT1521-3) VIN = 3.3V (LT1521-3.3) VIN = 5V (LT1521-5) VIN = 3.75V (LT1521) DEVICE IS OPERATING IN DROPOUT TJ = 25C
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Shutdown Pin Threshold (On-to-Off)
ILOAD = 1mA
TJ = 55C
50
250 150 200 100 OUTPUT CURRENT (mA)
300
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
LT1521 * TPC20
LT1521 * TPC21
LT1521/LT1521-3 LT1521-3.3/LT1521-5 TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Pin Threshold (Off-to-On)
2.0 1.8
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 -50 -25
SHUTDOWN PIN CURRENT (A)
ILOAD = 300mA
2.5 2.0 1.5 1.0 0.5 0 -50 -25
SHUTDOWN PIN INPUT CURRENT (mA)
SHUTDOWN PIN THRESHOLD (V)
ILOAD = 1mA
50 25 0 75 TEMPERATURE (C)
Adjust Pin Bias Current
200
50
REVERSE OUTPUT CURRENT (A)
ADJUST PIN BIAS CURRENT (nA)
175 150 125 100 75 50 25 0 -50 -25 0 75 50 25 TEMPERATURE (C) 100 125
40 35 30 25 20 15 10 5 0 0
SHORT-CIRCUIT CURRENT (A)
Current Limit
0.6 0.5 0.4 0.3 0.2 0.1 0 -50 -25 VIN = 7V VOUT = 0V
OUTPUT PIN CURRENT (A)
SHORT-CIRCUIT CURRENT (A)
RIPPLE REJECITON (dB)
50 25 75 0 TEMPERATURE (C)
UW
100
LT1521 * TPC22
Shutdown Pin Current
3.0 VSHDN = 0V 25
Shutdown Pin Input Current
20
15
10
5
125
50 25 75 0 TEMPERATURE (C)
100
125
0
0
1
7 3 8 2 5 6 4 SHUTDOWN PIN VOLTAGE (V)
9
LT1521 * TPC23
LT1521 * TPC24
Reverse Output Current
45 TJ = 25C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN VOUT = VSENSE (LT1521-3/LT1521-3.3 LT1521-5) VOUT = VADJ (LT1521) LT1521-3.3 LT1521-3 LT1521-5 1 2 345678 OUTPUT VOLTAGE (V) 9 10
Current Limit
0.6 VOUT = 0V 0.5 0.4 0.3 0.2 0.1 0
LT1521
0
1
4 3 5 2 INPUT VOLTAGE (V)
6
7
LT1521 * TPC25
LT1521 * TPC26
LT1521 * TPC27
Reverse Output Current
8 7 6 5 4 3 2 1 100 125 0 -50 -25 0 75 50 25 TEMPERATURE (C) 100 125 VIN = 0V VOUT = 3V (LT1521-3) VOUT = 3.3V (LT1521-3.3) VOUT = 5V (LT1521-5) VOUT = 3.75V (LT1521) 66 64 62 60 58 56 54
Ripple Rejection
VIN = VOUT (NOMINAL) + 1V + 0.5VP-P RIPPLE AT f = 120Hz ILOAD = 150mA
52 -50 -25
50 25 75 0 TEMPERATURE (C)
100
125
LT1521 * TPC28
LT1521 * TPC29
LT1521 * TPC30
7
LT1521/LT1521-3 LT1521-3.3/LT1521-5 TYPICAL PERFORMANCE CHARACTERISTICS
Ripple Rejection
100 90 80
RIPPLE REJECTION (dB)
ILOAD = 150mA VIN = 6V + 50mVRMS RIPPLE
LOAD REGULATION (mV)
70 60 50 40 30 20 10 0 10 100 COUT = 3.3F SOLID TANTALUM 1k 10k FREQUENCY (Hz) 100k 1M COUT = 33F SOLID TANTALUM
LT1521-5 Transient Response
OUTPUT VOLTAGE DEVIATION (V) 0.2 0.1 0 -0.1 -0.2 LOAD CURRENT (mA) LOAD CURRENT (mA) OUTPUT VOLTAGE DEVIATION (V) VIN = 6V CIN = 0.1F COUT = 1.5F
0.2 0.1 0 -0.1 -0.2
150 100 50 0 50 100 150 200 250 300 350 400 450 500 TIME (s)
LT1521 * TPC33
PIN FUNCTIONS
OUT (Pin 1): The output pin supplies power to the load. A minimum output capacitor of 1.5F is required to prevent oscillations, but larger values of output capacitor will be necessary to deal with larger load transients. See the Applications Information section for more on output capacitance and reverse output characteristics. SENSE (Pin 2): For fixed voltage versions of the LT1521 (LT1521-3, LT1521-3.3, LT1521-5), the sense pin is the input to the error amplifier. Optimum regulation will be obtained at the point where the sense pin is connected to the output pin of the regulator. In critical applications small voltage drops caused by the resistance (RP) of PC traces between the regulator and the load, which would normally degrade regulation, may be eliminated by connecting the sense pin to the output at the load as shown in Figure 1 (Kelvin Sense Connection). Note that the voltage drop across the external PC traces will add to the dropout voltage of the regulator. The sense pin bias current is 5A at the nominal regulated output voltage. This pin is internally clamped to - 0.6V (one VBE).
8
UW
Load Regulation
0 -5 -10 -15 LT1521* -20 -25 -30 -35 VIN = VOUT (NOMINAL + 1V) *VADJ = VOUT 0 50 75 25 TEMPERATURE (C) 100 125 ILOAD = 1mA TO 300mA LT1521-5 LT1521-3 LT1521-3.3
-40 -50 -25
LT1521 * TPC31
LT1521 * TPC32
LT1521-5 Transient Response
VIN = 6V CIN = 0.1F COUT = 33F
300 200 100 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 TIME (ms)
LT1521 * TPC34
U
U
U
LT1521/LT1521-3 LT1521-3.3/LT1521-5
PIN FUNCTIONS
5 IN LT1521 4 SHDN GND 3 RP
LT1521 * F01
+
VIN
Figure 1. Kelvin Sense Connection
ADJ (Pin 2): For adjustable LT1521, 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 50nA which flows into the pin. See Adjust Pin Bias Current vs Temperature in the Typical Performance Characteristics section. 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 20V. SHDN (Pin 5): The shutdown 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 1.7A. The shutdown pin is internally clamped to 7V and - 0.6V (one
APPLICATIONS INFORMATION
The LT1521 is a 300mA low dropout regulator with micropower quiescent current and shutdown. The device is capable of supplying 300mA at a dropout of 0.5V and operates with very low quiescent current (12A). In shutdown, the quiescent current drops to only 6A. In addition to the low quiescent current, the LT1521 incorporates several protection features which make it ideal for use in battery-powered 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 LT1521 acts like it has a diode in series with its output and prevents reverse current flow. Adjustable Operation The adjustable version of the LT1521 has an output voltage range of 3.75V to 20V. The output voltage is set by the ratio of two external resistors as shown in Figure 2. 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, 50nA at 25C, flows through R2 into the adjust pin. The output voltage can be calculated using the formula in Figure 2. 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
U
W
U
U
U
U
U
OUT
1
RP
SENSE
2
+
LOAD
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 5mA. A curve of the 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. IN (Pin 8): 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 battery rises with frequency, so it is advisable to include a bypass capacitor in battery-powered circuits. A bypass capacitor in the range of 1F to 10F is sufficient. The LT1521 is designed to withstand reverse voltages on the input pin with respect to ground and the output pin. In the case of reversed input, which can happen if a battery is plugged in backwards, the LT1521 will act as if there is a diode in series with its input. There will be no reverse current flow into the LT1521 and no reverse voltage will appear at the load. The device will protect both itself and the load.
9
LT1521/LT1521-3 LT1521-3.3/LT1521-5
APPLICATIONS INFORMATION
IN VIN SHDN GND VOUT = 3.75V 1 + R2 + (IADJ + R2) R1 VADJ = 3.75V IADJ = 50nA AT 25C OUTPUT RANGE = 3.75V TO 20V
LT1521 * F01
OUT
+
LT1521 ADJ R1 R2
))
Figure 2. Adjustable Operation
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 positive temperature coefficient of approximately 15ppm/C. The adjust pin bias current has a negative temperature coefficient. These effects 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 voltages 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 300mA is -20mV typical at VOUT = 3.75V. At VOUT = 12V, load regulation would be: (12V/3.75V)(- 20mV) = - 64mV Thermal Considerations The power handling capability of the device will be limited by the maximum rated junction temperature (125C). The 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)
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VOUT
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 LT1521 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. For surface mount devices, heat sinking 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. The following tables list thermal resistance 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 one ounce copper. All NC leads were connected to the ground plane.
Table 1. MS8 Package
COPPER AREA TOPSIDE** 2500mm2 1000mm2 225mm2 100mm2 BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 110C/W 115C/W 120C/W 130C/W
* Pin 4 is ground. ** Device is mounted on topside.
Table 2. S8 Package*
COPPER AREA TOPSIDE** BACKSIDE 2500mm2 1000mm2 225mm2 100mm2 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE BOARD AREA (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 2500mm2 60C/W 60C/W 68C/W 74C/W
* Pins 3, 6, 7 are ground. ** Device is mounted on topside.
LT1521/LT1521-3 LT1521-3.3/LT1521-5
APPLICATIONS INFORMATION
Table 3. SOT-223 Package (Thermal Resistance Junction-to-Tab 20C/W)
COPPER AREA TOPSIDE* 2500mm2 1000mm2 225mm2 100mm2 1000mm2 1000mm
2
BACKSIDE 2500mm2 2500mm2 2500mm2 2500mm2 1000mm2 0
BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 1000mm2 1000mm
2
THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 50C/W 50C/W 58C/W 64C/W 57C/W 60C/W
* Tab of device attached to topside copper.
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 150mA and a maximum ambient temperature of 50C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: IOUT(MAX)(VIN(MAX) - VOUT) + IGND(VIN(MAX)) Where, IOUT(MAX) = 150mA VIN(MAX) = 7V IGND at (IOUT = 150mA, VIN = 7V) = 2.1mA So, P = 150mA(7V - 3.3V) + (2.1mA)(7V) = 0.57W If we use a SOT-223 package, then the thermal resistance will be in the range of 50C/W to 65C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 0.57W(60C/W) = 34.2C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50C + 34.2C = 84.2C Output Capacitance and Transient Performance The LT1521 is designed to be stable with a wide range of output capacitors. A minimum output capacitor of 1.5F
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is required to prevent oscillations. The LT1521 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 for larger load current deltas. Bypass capacitors, used to decouple individual components powered by the LT1521, will increase the effective value of the output capacitor. Protection Features The LT1521 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 temperatures should not exceed 125C. The input of the device will withstand reverse voltages of 20V. 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 backward. For fixed voltage versions of the device, the output can be pulled below ground without damaging the device. If the input is left 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 voltage source, the output will source the 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.
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LT1521/LT1521-3 LT1521-3.3/LT1521-5
APPLICATIONS INFORMATION
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 4 summarizes the following information. The reverse output current will follow the curve in Figure 3 when the input 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 on the LT1521 unconnected when the output is held high. This can happen when the LT1521 is powered from a rectified AC source. If the AC source is removed, then the input of the LT1521 is effectively left floating. The reverse output current also follows the curve in Figure 3 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. When the input of the LT1521 is forced to a voltage below its nominal output voltage and its output is held high, the output current will follow the curve shown in Figure 3. This can happen if the input of the LT1521 is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or by 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 4). The state of the shutdown pin will have no effect on the reverse output current when the output is pulled above the input.
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REVERSE OUTPUT CURRENT (A)
45 40 35 30 25 20 15 10 5 0 0
INPUT CURRENT (A)
TJ = 25C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN VOUT = VSENSE (LT1521-3/LT1521-3.3 LT1521-5) VOUT = VADJ (LT1521) LT1521-3.3 LT1521-3
LT1521
LT1521-5 1 2 345678 OUTPUT VOLTAGE (V) 9 10 0 0 1 3 2 INPUT VOLTAGE (V) 4 5
LT1521 * F04
LT1521 * F03
Figure 3. Reverse Output Current
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5 VOUT = 3V (LT1521-3) VOUT = 3.3V (LT1521-3.3) VOUT = 5V (LT1521-5) LT1521-3.3 3
4
2
LT1521-3 LT1521-5
1
Figure 4. Input Current
LT1521/LT1521-3 LT1521-3.3/LT1521-5
APPLICATIONS INFORMATION
Table 4. Fault Conditions
INPUT PIN < VOUT (Nominal) < VOUT (Nominal) Open Open 0.8V 0.8V > 1.5V - 20V < VIN < 20V SHDN PIN Open (High) Grounded Open (High) Grounded Open (High) Grounded Open (High) Grounded OUTPUT/SENSE PINS Forced to VOUT (Nominal) Forced to VOUT (Nominal) > 1V > 1V 0V 0V 0V 0V RESULTING CONDITIONS Reverse Output Current 5A (See Figure 3) Input Current 1A (See Figure 4) Reverse Output Current 5A (See Figure 3) Input Current 1A (See Figure 4) Reverse Output Current 5A (See Figure 3) Reverse Output Current 5A (See Figure 3) Output Current = 0 Output Current = 0 Output Current = Short-Circuit Current Output Current = 0
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
0.007 (0.18) 0.021 0.006 (0.53 0.015)
0 - 6 TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
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MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102) 8 76 5
0.192 0.004 (4.88 0.10)
0.118 0.004** (3.00 0.102)
1 0.040 0.006 (1.02 0.15)
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4 0.034 0.004 (0.86 0.102)
0.006 0.004 (0.15 0.102)
MSOP (MS8) 1197
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LT1521/LT1521-3 LT1521-3.3/LT1521-5
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP 0.053 - 0.069 (1.346 - 1.752)
2
3
4
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
SO8 0996
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LT1521/LT1521-3 LT1521-3.3/LT1521-5
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted.
ST Package 3-Lead Plastic SOT-223
(LTC DWG # 05-08-1630)
0.248 - 0.264 (6.30 - 6.71) 0.116 - 0.124 (2.95 - 3.15)
0.264 - 0.287 (6.71 - 7.29) 0.130 - 0.146 (3.30 - 3.71)
0.090 (2.29) NOM
0.033 - 0.041 (0.84 - 1.04)
10 - 16 0.071 (1.80) MAX 10 MAX 0.010 - 0.014 (0.25 - 0.36)
10 - 16 0.025 - 0.033 (0.64 - 0.84) 0.181 (4.60) NOM 0.012 (0.31) MIN 0.0008 - 0.0040 (0.0203 - 0.1016)
ST3 (SOT-233) 0792
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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LT1521/LT1521-3 LT1521-3.3/LT1521-5 RELATED PARTS
PART NUMBER LTC 1174 LT1175 LT1120A LT1304 LT1529
(R)
DESCRIPTION 425mA High Efficiency Step-Down Switching Regulator 500mA Micropower Low Dropout Negative Linear Regulator 125mA Micropower Low Dropout Linear Regulator Micropower Step-Up DC/DC Converter 3A Micropower Low Dropout Regulator
COMMENTS >90% Efficiency, SO-8 Package Selectable Current Limit 20A Quiescent Current, Includes Comparator 15A Quiescent Current, 1.5 Minimum Input 50A Quiescent 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
1521335fa LT/TP 0299 REV A 2K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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