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LT1764A Series 3A, Fast Transient Response, Low Noise, LDO Regulators
FEATURES

DESCRIPTIO
Optimized for Fast Transient Response Output Current: 3A Dropout Voltage: 340mV at 3A Low Noise: 40VRMS (10Hz to 100kHz) 1mA Quiescent Current Wide Input Voltage Range: 2.7V to 20V No Protection Diodes Needed Controlled Quiescent Current in Dropout Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 3.3V Adjustable Output from 1.21V to 20V < 1A Quiescent Current in Shutdown Stable with 10F Output Capacitor* Stable with Ceramic Capacitors* Reverse Battery Protection No Reverse Current Thermal Limiting
APPLICATIO S

The LT (R)1764A is a low dropout regulator optimized for fast transient response. The device is capable of supplying 3A of output current with a dropout voltage of 340mV. Operating quiescent current is 1mA, dropping to < 1A in shutdown. Quiescent current is well controlled; it does not rise in dropout as it does with many other regulators. In addition to fast transient response, the LT1764A has very low output voltage noise which makes the device ideal for sensitive RF supply applications. Output voltage range is from 1.21V to 20V. The LT1764A regulators are stable with output capacitors as low as 10F. Internal protection circuitry includes reverse battery protection, current limiting, thermal limiting and reverse current protection. The device is available in fixed output voltages of 1.5V, 1.8V, 2.5V, 3.3V and as an adjustable device with a 1.21V reference voltage. The LT1764A regulators are available in 5-lead TO-220 and DD packages, and 16-lead FE packages.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. *See Applications Information Section.
3.3V to 2.5V Logic Power Supply Post Regulator for Switching Supplies
TYPICAL APPLICATIO
400
3.3VIN to 2.5VOUT Regulator
DROPOUT VOLTAGE (mV)
2.5V 3A 10F* LT1764A-2.5 SHDN SENSE GND
1764 TA01
350 300 250 200 150 100 50 0 0 0.5 1.0 1.5 2.0 LOAD CURRENT (A) 2.5 3.0
1764 TA02
+
VIN > 3V 10F*
IN
OUT
+
*TANTALUM, CERAMIC OR ALUMINUM ELECTROLYTIC
U
Dropout Voltage
1764afb
U
U
1
LT1764A Series
ABSOLUTE MAXIMUM RATINGS (Note 1)
IN Pin Voltage ........................................................ 20V OUT Pin Voltage .................................................... 20V Input to Output Differential Voltage (Note 12) ....... 20V SENSE Pin Voltage ............................................... 20V ADJ Pin Voltage ...................................................... 7V SHDN Pin Voltage ................................................. 20V Output Short-Circuit Duration ......................... Indefinite Operating Junction Temperature Range E Grade ............................................. - 40C to 125C MP Grade ......................................... - 55C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
PACKAGE/ORDER INFORMATION
TOP VIEW
FRONT VIEW 5 4 TAB IS GND 3 2 1 Q PACKAGE 5-LEAD PLASTIC DD SENSE/ADJ* OUT GND IN SHDN
TAB IS GND
FRONT VIEW
5 4 3 2 1
T PACKAGE 5-LEAD PLASTIC TO-220
*PIN 5 = SENSE FOR LT1764A-1.5/LT1764A-1.8/ LT1764A-2.5/LT1764A-3.3 = ADJ FOR LT1764A TJMAX = 150C, JA = 30C/ W
*PIN 5 = SENSE FOR LT1764A-1.5/LT1764A-1.8/ LT1764A-2.5/LT1764A-3.3 = ADJ FOR LT1764A TJMAX = 150C, JA = 50C/ W
ORDER PART NUMBER LT1764AEQ LT1764AEQ-1.5 LT1764AEQ-1.8 LT1764AEQ-2.5 LT1764AEQ-3.3 LT1764AMPQ
Order Options Tape and Reel: Add #TR
ORDER PART NUMBER LT1764AET LT1764AET-1.5 LT1764AET-1.8 LT1764AET-2.5 LT1764AET-3.3
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.
ELECTRICAL CHARACTERISTICS
The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. (Note 2)
PARAMETER Minimum Input Voltage (Notes 3, 11) CONDITIONS ILOAD = 0.5A ILOAD = 1.5A E Grade: ILOAD = 3A MP Grade: ILOAD = 3A LT1764A-1.5 VIN = 2.21V, ILOAD = 1mA 2.7V < VIN < 20V, 1mA < ILOAD < 3A LT1764A-1.8 VIN = 2.3V, ILOAD = 1mA 2.8V < VIN < 20V, 1mA < ILOAD < 3A MIN TYP 1.7 1.9 2.3 2.3 1.477 1.447 1.773 1.737 1.500 1.500 1.800 1.800 MAX UNITS V V V V V V V V
1764afb
Regulated Output Voltage (Note 4)
2
U
U
W
WW U
W
SENSE/ ADJ* OUT GND IN SHDN
GND NC OUT OUT OUT SENSE/ADJ* GND GND
1 2 3 4 5 6 7 8 17
16 GND 15 NC 14 IN 13 IN 12 IN 11 NC 10 SHDN 9 GND
*PIN 6 = SENSE FOR LT1764A-1.5/ LT1764A-1.8/LT1764A-2.5/ LT1764A-3.3 = ADJ FOR LT1764A
FE PACKAGE 16-LEAD PLASTIC TSSOP PIN 17 IS GND
TJMAX = 150C, JA = 38C/ W
ORDER PART NUMBER LT1764AEFE LT1764AEFE-1.5 LT1764AEFE-1.8 LT1764AEFE-2.5 LT1764AEFE-3.3
FE PART MARKING LT1764AEFE LT1764AEFE-1.5 LT1764AEFE-1.8 LT1764AEFE-2.5 LT1764AEFE-3.3

2.7 2.8 1.523 1.545 1.827 1.854
LT1764A Series
The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. (Note 2)
PARAMETER CONDITIONS LT1764A-2.5 VIN = 3V, ILOAD = 1mA 3.5V < VIN < 20V, 1mA < ILOAD < 3A LT1764A-3.3 VIN = 3.8V, ILOAD = 1mA 4.3V < VIN < 20V, 1mA < ILOAD < 3A ADJ Pin Voltage (Notes 3, 4) Line Regulation LT1764A VIN = 2.21V, ILOAD = 1mA E Grade: 2.7V < VIN < 20V, 1mA < ILOAD < 3A MP Grade: 2.8V < VIN < 20V, 1mA < ILOAD < 3A VIN = 2.21V to 20V, ILOAD = 1mA VIN = 2.3V to 20V, ILOAD = 1mA VIN = 3V to 20V, ILOAD = 1mA VIN = 3.8V to 20V, ILOAD = 1mA VIN = 2.21V to 20V, ILOAD = 1mA VIN = 2.7V, ILOAD = 1mA to 3A VIN = 2.7V, ILOAD = 1mA to 3A VIN = 2.8V, ILOAD = 1mA to 3A VIN = 2.8V, ILOAD = 1mA to 3A VIN = 3.5V, ILOAD = 1mA to 3A VIN = 3.5V, ILOAD = 1mA to 3A VIN = 4.3V, ILOAD = 1mA to 3A VIN = 4.3V, ILOAD = 1mA to 3A

ELECTRICAL CHARACTERISTICS
MIN 2.462 2.412 3.250 3.183 1.192 1.168 1.168
TYP 2.500 2.500 3.300 3.300 1.210 1.210 1.210 2.5 3 4 4.5 2 3 4
MAX 2.538 2.575 3.350 3.400 1.228 1.246 1.246 10 10 10 10 10 7 23 8 25 10 30 12 40 5 20 20 0.05 0.10 0.13 0.18 0.20 0.27 0.33 0.40 0.45 0.66 1.5 1.6 5 18 75 200 10 2 1 30 1
UNITS V V V V V V V mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV V V V V V V V V V V mA mA mA mA mA mA VRMS A V V A A A dB
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LT1764A-1.5 LT1764A-1.8 LT1764A-2.5 LT1764A-3.3 LT1764A (Note 3) LT1764A-1.5 LT1764A-1.8 LT1764A-2.5 LT1764A-3.3
Load Regulation
4
4
LT1764A (Note 3) VIN = 2.7V, ILOAD = 1mA to 3A E Grade: VIN = 2.7V, ILOAD = 1mA to 3A MP Grade: VIN = 2.8V, ILOAD = 1mA to 3A Dropout Voltage VIN = VOUT(NOMINAL) (Notes 5, 6, 11) ILOAD = 1mA ILOAD = 1mA ILOAD = 100mA ILOAD = 100mA ILOAD = 500mA ILOAD = 500mA ILOAD = 1.5A ILOAD = 1.5A ILOAD = 3A ILOAD = 3A GND Pin Current VIN = VOUT(NOMINAL) + 1V (Notes 5, 7) ILOAD = 0mA ILOAD = 1mA ILOAD = 100mA ILOAD = 500mA ILOAD = 1.5A ILOAD = 3A COUT = 10F, ILOAD = 3A, BW = 10Hz to 100kHz (Notes 3, 8) VOUT = Off to On VOUT = On to Off VSHDN = 0V VSHDN = 20V VIN = 6V, VSHDN = 0V VIN - VOUT = 1.5V (Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 1.5A
2

0.02
0.07
0.14
0.25
0.34

1 1.1 3.5 11 40 120 40 3
Output Voltage Noise ADJ Pin Bias Current Shutdown Threshold SHDN Pin Current (Note 9) Quiescent Current in Shutdown Ripple Rejection

0.25
0.9 0.75 0.01 7 0.01
55
63
3
LT1764A Series
ELECTRICAL CHARACTERISTICS
The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. (Note 2)
PARAMETER Current Limit CONDITIONS VIN = 7V, VOUT = 0V E Grade: LT1764A; LT1764A-1.5; VIN = 2.7V, VOUT = - 0.1V MP Grade: LT1764A VIN = 2.8V, VOUT = - 0.1V Input Reverse Leakage Current VIN = - 20V, VOUT = 0V Reverse Output Current (Note 10) LT1764A-1.5 VOUT = 1.5V, VIN < 1.5V LT1764A-1.8 VOUT = 1.8V, VIN < 1.8V LT1764A-2.5 VOUT = 2.5V, VIN < 2.5V LT1764A-3.3 VOUT = 3.3V, VIN < 3.3V LT1764A (Note 3) VOUT = 1.21V, VIN < 1.21V 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 LT1764A regulators are tested and specified under pulse load conditions such that TJ TA. The LT1764A (E grade) is 100% tested at TA = 25C; performance at - 40C and 125C is assured by design, characterization and correlation with statistical process controls. The LT1764A (MP grade) is 100% tested and guaranteed over the -55C to 125C temperature range. Note 3: The LT1764A (adjustable version) is tested and specified for these conditions with the ADJ pin connected to the OUT pin. 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: To satisfy requirements for minimum input voltage, the LT1764A (adjustable version) is tested and specified for these conditions with an external resistor divider (two 4.12k resistors) for an output voltage of

MIN 3.1 3.1
TYP 4
MAX
UNITS A A A
1 600 600 600 600 300 1200 1200 1200 1200 600
mA A A A A A
2.42V. The external resistor divider will add a 300A DC load on the output. Note 6: Dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. In dropout, the output voltage will be equal to: VIN - VDROPOUT. Note 7: GND pin current is tested with VIN = VOUT(NOMINAL) + 1V or VIN = 2.7V (E grade) or VIN = 2.8V (MP grade), whichever is greater, and a current source load. The GND pin current will decrease at higher input voltages. Note 8: ADJ pin bias current flows into the ADJ pin. Note 9: SHDN pin current flows into the SHDN pin. Note 10: Reverse output current is tested with the IN pin grounded and the OUT pin forced to the rated output voltage. This current flows into the OUT pin and out the GND pin. Note 11. For the LT1764A, LT1764A-1.5 and LT1764A-1.8 dropout voltage will be limited by the minimum input voltage specification under some output voltage/load conditions. Note 12. All combinations of absolute maximum input voltage and absolute maximum output voltage cannot be achieved. The absolute maximum differential from input to output is 20V. For example, with VIN = 20V, VOUT cannot be pulled below ground.
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Dropout Voltage
600 GUARANTEED DROPOUT VOLTAGE (mV) 500
DROPOUT VOLTAGE (mV)
700 600 500 TJ 125C 400 300 TJ 25C 200 100 0
DROPOUT VOLTAGE (mV)
400 TJ = 125C 300 200 TJ = 25C 100 0
0
0.5
1.0 1.5 2.0 OUTPUT CURRENT (A)
4
UW
2.5
Guaranteed Dropout Voltage
= TEST POINTS 600 500 400
Dropout Voltage
IL = 3A 300 IL = 1.5A 200 IL = 0.5A 100 0 -50 -25 IL = 100mA IL = 1mA
3.0
1764 G01
0
0.5
2.0 1.5 1.0 OUTPUT CURRENT (A)
2.5
3.0
1764 G02
50 25 75 0 TEMPERATURE (C)
100
125
1764 G03
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LT1764A Series TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
1.4 1.2
QUIESCENT CURRENT (mA)
LT1764A-1.5/1.8/2.5/3.3
OUTPUT VOLTAGE (V)
1.0 LT1764A 0.8 0.6 0.4 0.2
1.51 1.50 1.49 1.48 1.47
OUTPUT VOLTAGE (V)
0 -50 -25
VIN = 6V RL = IL = 0 VSHDN = VIN 50 25 75 0 TEMPERATURE (C) 100 125
LT1764A-2.5 Output Voltage
2.58 2.56 IL = 1mA 3.38 3.36
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
2.52 2.50 2.48 2.46 2.44 2.42 - 50 - 25 0 75 50 25 TEMPERATURE (C) 100 125
3.32 3.30 3.28 3.26 3.24 3.22 - 50 - 25 0 75 50 25 TEMPERATURE (C) 100 125
ADJ PIN VOLTAGE (V)
2.54
LT1764A-1.5 Quiescent Current
40 35 TJ = 25C RL = VSHDN = VIN 40 35
QUIESCENT CURRENT (mA)
30 25 20 15 10 5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
UW
1764 G04 1756 G06 1764 G41
LT1764A-1.5 Output Voltage
1.54 IL = 1mA 1.53 1.52 1.83 1.82 1.81 1.80 1.79 1.78 1.77 0 50 75 25 TEMPERATURE (C) 100 125 1.84
LT1764A-1.8 Output Voltage
IL = 1mA
1.46 - 50 - 25
1.76 - 50 - 25
0
75 50 25 TEMPERATURE (C)
100
125
1764A G40
1756 G05
LT1764A-3.3 Output Voltage
IL = 1mA 1.230 1.225 1.220 1.215 1.210 1.205 1.200 1.195
LT1764A ADJ Pin Voltage
IL = 1mA
3.34
1.190 - 50 - 25
0
75 50 25 TEMPERATURE (C)
100
125
1756 G07
1756 G08
LT1764A-1.8 Quiescent Current
40 TJ = 25C RL = VSHDN = VIN 35 30 25 20 15 10 5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
LT1764A-2.5 Quiescent Current
TJ = 25C RL = VSHDN = VIN
30 25 20 15 10 5 0
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
1764 G09
1764 G10
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5
LT1764A Series TYPICAL PERFOR A CE CHARACTERISTICS
LT1764A-3.3 Quiescent Current
40 35 TJ = 25C RL = VSHDN = VIN
QUIESCENT CURRENT (mA)
GND PIN CURRENT (mA)
30 25 20 15 10 5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10
QUIESCENT CURRENT (mA)
LT1764A-1.8 GND Pin Current
20.0 17.5
GND PIN CURRENT (mA)
40
TJ = 25C VSHDN = VIN *FOR VOUT = 1.8V
GND PIN CURRENT (mA)
12.5 10.0 7.5 5.0 2.5 0 0 1 2
RL = 3.6 IL = 500mA*
RL = 6 IL = 300mA*
25 20 15 10 5 0
RL = 5 IL = 500mA*
GND PIN CURRENT (mA)
15.0
RL = 18 IL = 100mA* 34567 INPUT VOLTAGE (V) 8 9 10
LT1764A GND Pin Current
15 TJ = 25C VSHDN = VIN *FOR VOUT = 1.21V
GND PIN CURRENT (mA)
12
GND PIN CURRENT (mA)
RL = 2.42 IL = 500mA* 9 RL = 4.33 IL = 300mA* 6 RL = 12.1 IL = 100mA* 3
GND PIN CURRENT (mA)
0
0
1
2
34567 INPUT VOLTAGE (V)
6
UW
1764 G11
LT1764A Quiescent Current
1.6 TJ = 25C 1.4 RL = 4.3k VSHDN = VIN 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
1764 G12
LT1764A-1.5 GND Pin Current
20.0 17.5 15.0 12.5 10.0 7.5 5.0 2.5 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 RL = 15 IL = 100mA* RL = 3 IL = 500mA* RL = 5 IL = 300mA* TJ = 25C VSHDN = VIN *FOR VOUT = 1.5V
1764 G42
LT1764A-2.5 GND Pin Current
80 TJ = 25C VSHDN = VIN *FOR VOUT = 2.5V 70 60 50 40 30 20 10 0 0 1 2 34567 INPUT VOLTAGE (V) 8 9 10 35 30
LT1764A-3.3 GND Pin Current
TJ = 25C VSHDN = VIN *FOR VOUT = 3.3V
RL = 6.6 IL = 500mA* RL = 11 IL = 300mA* RL = 33 IL = 100mA*
RL = 25 IL = 100mA*
RL = 8.33 IL = 300mA*
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
1764 G13
1764 G14
1764 G15
LT1764A-1.5 GND Pin Current
150 TJ = 25C VSHDN = VIN *FOR VOUT = 1.5V
150
LT1764A-1.8 GND Pin Current
TJ = 25C VSHDN = VIN *FOR VOUT = 1.8V RL = 0.6 IL = 3A*
120 RL = 0.5 IL = 3A* RL = 1 IL = 1.5A*
120
90
90
60
RL = 2.14 IL = 0.7A*
60
RL = 1.2 IL = 1.5A*
RL = 2.57 IL = 0.7A*
30
30
0 8 9 10
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
0
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
1764 G16
1764A G43
1764 G17
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LT1764A Series TYPICAL PERFOR A CE CHARACTERISTICS
LT1764A-2.5 GND Pin Current
200 TJ = 25C VSHDN = VIN *FOR VOUT = 2.5V
GND PIN CURRENT (mA)
GND PIN CURRENT (mA)
GND PIN CURRENT (mA)
160
120
RL = 0.83 IL = 3A*
80 RL = 1.66 IL = 1.5A* RL = 3.57 IL = 0.7A*
40
0
0
1
2
34567 INPUT VOLTAGE (V)
GND Pin Current vs ILOAD
160 140
SHDN PIN THRESHOLD (V)
VIN = VOUT(NOM) + 1V
120 100 80 60 40 20 0 0 0.5 2.0 1.5 OUTPUT CURRENT (A) 1.0 2.5 3.0
1764 G21
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
SHDN PIN THRESHOLD (V)
GND PIN CURRENT (mA)
SHDN Pin Input Current
10 9
10 9
SHDN PIN INPUT CURRENT (A)
SHDN PIN INPUT CURRENT (A)
ADJ PIN BIAS CURRENT (A)
8 7 6 5 4 3 2 1 0 0 2 4 6 8 10 12 14 16 18 20 SHDN PIN VOLTAGE (V)
1764 G24
UW
8 9
1764 G18
LT1764A-3.3 GND Pin Current
200 TJ = 25C VSHDN = VIN *FOR VOUT = 3.3V RL = 1.1 IL = 3A*
150
LT1764A GND Pin Current
TJ = 25C VSHDN = VIN *FOR VOUT = 1.21V RL = 0.4 IL = 3A* 90 RL = 0.81 IL = 1.5A*
160
120
120
80 RL = 2.2 IL = 1.5A* 40 RL = 4.71 IL = 0.7A*
60
RL = 1.73 IL = 0.7A*
30
0
10
0
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
0
1
2
34567 INPUT VOLTAGE (V)
8
9
10
1764 G19
1764 G20
SHDN Pin Threshold (On-to-Off)
1.0 0.9 0.8 IL = 1mA
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
SHDN Pin Threshold (Off-to-On)
IL = 3A
IL = 1mA
0 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1764 G22
1764 G23
SHDN Pin Input Current
VSHDN = 20V
ADJ Pin Bias Current
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
8 7 6 5 4 3 2 1 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125
0 - 50 - 25
0
75 50 25 TEMPERATURE (C)
100
125
1764 G25
1756 G26
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7
LT1764A Series TYPICAL PERFOR A CE CHARACTERISTICS
Current Limit
6 5 TJ = -50C
CURRENT LIMIT (A) 6 5
CURRENT LIMIT (A)
REVERSE OUTPUT CURRENT (mA)
4 3 2 1 0 0 2 4 6 8 10 12 14 16 18 20 INPUT/OUTPUT DIFFERENTIAL (V)
1764 G27
TJ = 125C TJ = 25C
Reverse Output Current
1.0 VOUT = 1.21V (LT1764A) 0.9 VOUT = 1.5V (LT1764A-1.5) = 1.8V (LT1764A-1.8) V 0.8 VOUT = 2.5V (LT1764A-2.5) OUT 0.7 VOUT = 3.3V (LT1764A-3.3) 0.6 0.5 0.4 0.3 0.2 0.1 0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 LT1764A VIN = 0V
REVERSE OUTPUT CURRENT (mA)
RIPPLE REJECTION (dB)
LT1764A-1.5/1.8/-2.5/-3.3
50 40 30
COUT = 100F TANTALUM + 10 x 1F CERAMIC
RIPPLE REJECTION (dB)
LT1764A Minimum Input Voltage
3.0 2.5 2.0 IL = 1.5A 1.5 IL = 500mA 1.0 0.5 0 -50 -25 IL = 100mA
10 5
OUTPUT NOISE SPECTRAL DENSITY (V/Hz)
MINIMUM INPUT VOLTAGE (V)
LOAD REGULATION (mV)
IL = 3A
50 25 75 0 TEMPERATURE (C)
8
UW
1764 G30
Current Limit
VIN = 7V VOUT = 0V 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -50 -25 0 50 25 75 0 TEMPERATURE (C) 100 125
Reverse Output Current
LT1764A-1.5 LT1764A-1.8 LT1764A-2.5 LT1764A-3.3 LT1764A TJ = 25C VIN = 0V CURRENT FLOWS INTO OUTPUT PIN VOUT = VADJ (LT1764A) VOUT = VFB (LT1764A-1.5/1.8/-2.5/-3.3) 0 1 2 345678 OUTPUT VOLTAGE (V) 9 10
4 3 2 1
1764 G28
1764 G29
Ripple Rejection
80 70 60
Ripple Rejection
75 IL = 1.5A VIN = VOUT(NOM) + 1V + 0.5VP-P RIPPLE AT f = 120Hz
70
65
60
COUT = 10F IL = 1.5A TANTALUM 10 VIN = VOUT(NOM) + 1V + 50mVRMS RIPPLE 0 100 100k 10 1k 10k FREQUENCY (Hz)
20
55
1M
50 -50 -25
50 25 0 75 TEMPERATURE (C)
100
125
1764 G31
1764 G32
Load Regulation
1
Output Noise Spectral Density
COUT = 10F ILOAD = 3A
0 -5 -10 -15 -20 -25
LT1764A
LT1764A-1.5 LT1764A-1.8 LT1764A-2.5 LT1764A-3.3 IL = 1mA TO 3A VIN = 2.7V (LT1764A/LT1764A-1.5) VIN = VOUT(NOM) + 1V (LT1764A-1.8/-2.5/-3.3) 0 75 50 25 TEMPERATURE (C) 100 125
LT1764A-3.3 0.1
LT1764A-2.5
LT1764A
LT1764A-1.8 LT1764A-1.5
100
125
-30 - 50 - 25
0.01 10
100
1k 10k FREQUENCY (Hz)
100k
1764 G35
1764 G33
1764 G34
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LT1764A Series TYPICAL PERFOR A CE CHARACTERISTICS
RMS Output Noise vs Load Current (10Hz to 100kHz)
40 35 COUT = 10F LT1764A-3.3
OUTPUT NOISE (VRMS)
30 25
20 15 LT1764A-1.5 10 5 0 0.0001 0.001 0.01 0.1 LOAD CURRENT (A) 1 10
1764 G36
LT1764A-3.3 Transient Response
OUTPUT VOLTAGE DEVIATION (V) OUTPUT VOLTAGE DEVIATION (V)
0.2 0.1 0 -0.1 -0.2 1.00 VIN = 4.3V CIN = 3.3F TANTALUM COUT = 10F TANTALUM
LOAD CURRENT (A)
LOAD CURRENT (A)
0.75 0.50 0.25 0 0 2 4 6 8 10 12 14 16 18 20 TIME (s)
1764 G38
UW
LT1764A-3.3 10Hz to 100kHz Output Noise
LT1764A-2.5
LT1764A-1.8
VOUT 100V/DIV
LT1764A
COUT = 10F IL = 3A
1ms/DIV
1764A G37
LT1764A-3.3 Transient Response
0.2 0.1 0 -0.1 -0.2 VIN = 4.3V CIN = 33F COUT = 100F TANTALUM + 10 x 1F CERAMIC
3 2 1 0 0 2 4 6 8 10 12 14 16 18 20 TIME (s)
1764 G39
1764afb
9
LT1764A Series
PI FU CTIO S
SHDN (Pin 1/1/10): Shutdown. The SHDN pin is used to put the LT1764A regulators into a low power shutdown state. The output will be off when the SHDN pin is pulled low. The SHDN pin can be driven either by 5V logic or open-collector logic with a pull-up resistor. The pull-up resistor is required to supply the pull-up current of the open-collector gate, normally several microamperes, and the SHDN pin current, typically 7A. If unused, the SHDN pin must be connected to VIN. The device will be in the low power shutdown state if the SHDN pin is not connected. IN (Pin 2/Pin 2/Pins 12, 13, 14): Input. Power is supplied to the device through the IN pin. A bypass capacitor is required on this pin 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 advisable to include a bypass capacitor in batterypowered circuits. A bypass capacitor in the range of 1F to 10F is sufficient. The LT1764A regulators are designed to withstand reverse voltages on the IN pin with respect to ground and the OUT pin. In the case of a reverse input, which can happen if a battery is plugged in backwards, the device will act as if there is a diode in series with its input. There will be no reverse current flow into the regulator and no reverse voltage will appear at the load. The device will protect both itself and the load. NC (Pins 2, 11, 15) TSSOP Only: No Connect. GND (Pin 3/Pin 3/Pins 1, 7, 8, 9, 16, 17): Ground. OUT (Pin 4/Pin 4/Pins 3, 4, 5): Output. The output supplies power to the load. A minimum output capacitor of 10F is required to prevent oscillations. Larger output capacitors will be required for applications with large transient loads to limit peak voltage transients. See the
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DD/TO-220/TSSOP
Applications Information section for more information on output capacitance and reverse output characteristics. SENSE (Pin 5/Pin 5/Pin 6): Sense. For fixed voltage versions of the LT1764A (LT1764A-1.5/LT1764A-1.8/ LT1764A-2.5/LT1764A-3.3), 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 OUT pin of the regulator. In critical applications, small voltage drops are caused by the resistance (RP) of PC traces between the regulator and the load. These 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 600A at the nominal rated output voltage. The SENSE pin can be pulled below ground (as in a dual supply system where the regulator load is returned to a negative supply) and still allow the device to start and operate. ADJ (Pin 5/Pin 5/Pin 6): Adjust. For the adjustable LT1764A, this is the input to the error amplifier. This pin is internally clamped to 7V. It has a bias current of 3A which flows into the pin. The ADJ pin voltage is 1.21V referenced to ground and the output voltage range is 1.21V to 20V.
2
IN OUT LT1764A
4
RP
+
VIN
1
SHDN
SENSE GND
5
+
LOAD
3
RP
1764 F01
Figure 1. Kelvin Sense Connection
1764afb
LT1764A Series
APPLICATIO S I FOR ATIO
The LT1764A series are 3A low dropout regulators optimized for fast transient response. The devices are capable of supplying 3A at a dropout voltage of 340mV. The low operating quiescent current (1mA) drops to less than 1A in shutdown. In addition to the low quiescent current, the LT1764A regulators incorporate several protection features which make them ideal for use in battery-powered systems. The devices are protected against both reverse input 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 LT1764A-X acts like it has a diode in series with its output and prevents reverse current flow. Additionally, in dual supply applications where the regulator load is returned to a negative supply, the output can be pulled below ground by as much as 20V and still allow the device to start and operate. Adjustable Operation The adjustable version of the LT1764A has an output voltage range of 1.21V to 20V. The output voltage is set by the ratio of two external resistors as shown in Figure 2. The device servos the output to maintain the voltage at the ADJ pin at 1.21V referenced to ground. The current in R1 is then equal to 1.21V/R1 and the current in R2 is the current in R1 plus the ADJ pin bias current. The ADJ pin bias current, 3A at 25C, flows through R2 into the ADJ pin. The output voltage can be calculated using the formula in Figure 2. The value of R1 should be less than 4.17k to minimize errors in the output voltage caused by the ADJ pin bias current. Note that in shutdown the output is turned off and the divider current will be zero. The adjustable device is tested and specified with the ADJ pin tied to the OUT pin for an output voltage of 1.21V. Specifications for output voltages greater than 1.21V will be proportional to the ratio of the desired output voltage to 1.21V: VOUT/1.21V. For example, load regulation for an output current change of 1mA to 3A is - 3mV typical at VOUT = 1.21V. At VOUT = 5V, load regulation is: (5V/1.21V)(-3mV) = - 12.4mV
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IN VIN OUT VOUT
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LT1764A ADJ GND R1
1764 F02
R2
R2 VOUT = 1.21V 1 + + (IADJ )(R2) R1 VADJ = 1.21V IADJ = 3A AT 25C OUTPUT RANGE = 1.21V TO 20V
Figure 2. Adjustable Operation
Output Capacitors and Stability The LT1764A regulator is a feedback circuit. Like any feedback circuit, frequency compensation is needed to make it stable. For the LT1764A, the frequency compensation is both internal and external--the output capacitor. The size of the output capacitor, the type of the output capacitor, and the ESR of the particular output capacitor all affect the stability. In addition to stability, the output capacitor also affects the high frequency transient response. The regulator loop has a finite band width. For high frequency transient loads, recovery from a transient is a combination of the output capacitor and the bandwidth of the regulator. The LT1764A was designed to be easy to use and accept a wide variety of output capacitors. However, the frequency compensation is affected by the output capacitor and optimum frequency stability may require some ESR, especially with ceramic capacitors. For ease of use, low ESR polytantalum capacitors (POSCAP) are a good choice for both the transient response and stability of the regulator. These capacitors have intrinsic ESR that improves the stability. Ceramic capacitors have extremely low ESR, and while they are a good choice in many cases, placing a small series resistance element will sometimes achieve optimum stability and minimize ringing. In all cases, a minimum of 10F is required while the maximum ESR allowable is 3. The place where ESR is most helpful with ceramics is low output voltage. At low output voltages, below 2.5V, some ESR helps the stability when ceramic output capacitors are used. Also, some ESR allows a smaller capacitor value to be used. When small signal ringing occurs with ceramics due to insufficient ESR, adding ESR or increas1764afb
11
LT1764A Series
APPLICATIO S I FOR ATIO
ing the capacitor value improves the stability and reduces the ringing. Table 1 gives some recommended values of ESR to minimize ringing caused by fast, hard current transitions.
Table 1. Capacitor Minimum ESR
VOUT 1.2V 1.5V 1.8V 2.5V 3.3V 5V 10F 10m 7m 5m 0m 0m 0m 22F 5m 5m 5m 0m 0m 0m 47F 3m 3m 3m 0m 0m 0m 100F 0m 0m 0m 0m 0m 0m
Figures 3 through 8 show the effect of ESR on the transient response of the regulator. These scope photos show the transient response for the LT1764A at three different output voltages with various capacitors and various values of ESR. The output load conditions are the same for all traces. In all cases there is a DC load of 1A. The load steps up to 2A at the first transition and steps back to 1A at the second transition. At the worst case point of 1.2VOUT with 10F COUT (Figure 3), a minimum amount of ESR is required. While 5m is enough to eliminate most of the ringing, a value closer to 20m provides a more optimum response. At 2.5V output with 10F COUT (Figure 4) the output rings at the transitions with 0 ESR but still settles to within 10mV in 20s after the 1A load step. Once again a small value of ESR will provide a more optimum response. At 5VOUT with 10F COUT (Figure 5) the response is well damped with 0 ESR. With a COUT of 100F at 0 ESR and an output of 1.2V (Figure 6), the output rings although the amplitude is only 10mVp-p. With COUT of 100F it takes only 5m to 20m of ESR to provide good damping at 1.2V output. Performance at 2.5V and 5V output with 100F COUT shows similar characteristics to the 10F case (see Figures 7-8). At 2.5VOUT 5m to 20m can improve transient response. At 5VOUT the response is well damped with 0 ESR.
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Capacitor types with inherently higher ESR can be combined with 0m ESR ceramic capacitors to achieve both good high frequency bypassing and fast settling time. Figure 9 illustrates the improvement in transient response that can be seen when a parallel combination of ceramic and POSCAP capacitors are used. The output voltage is at the worst case value of 1.2V. Trace A, is with a 10F ceramic output capacitor and shows significant ringing with a peak amplitude of 25mV. For Trace B, a 22F/45m POSCAP is added in parallel with the 10F ceramic. The output is well damped and settles to within 10mV in less than 5s. For Trace C, a 100F/35m POSCAP is connected in parallel with the 10F ceramic capacitor. In this case the peak output deviation is less than 20mV and the output settles in about 5s. For improved transient response the value of the bulk capacitor (tantalum or aluminum electrolytic) should be greater than twice the value of the ceramic capacitor. Tantalum and Polytantalum Capacitors There is a variety of tantalum capacitor types available, with a wide range of ESR specifications. Older types have ESR specifications in the hundreds of m to several Ohms. Some newer types of polytantalum with multielectrodes have maximum ESR specifications as low as 5m. In general the lower the ESR specification, the larger the size and the higher the price. Polytantalum capacitors have better surge capability than older types and generally lower ESR. Some types such as the Sanyo TPE and TPB series have ESR specifications in the 20m to 50m range, which provide near optimum transient response. Aluminum Electrolytic Capacitors Aluminum electrolytic capacitors can also be used with the LT1764. These capacitors can also be used in conjunction with ceramic capacitors. These tend to be the cheapest and lowest performance type of capacitors. Care must be used in selecting these capacitors as some types can have ESR which can easily exceed the 3 maximum value.
1764afb
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LT1764A Series
0 5 VOUT = 1.2V IOUT = 1A WITH 1A PULSE COUT = 10F CERAMIC 0 VOUT = 1.2V IOUT = 1A WITH 1A PULSE COUT = 100F CERAMIC
RESR (m)
RESR (m)
5
20mV/DIV
50mV/DIV
10 20 50 20s/DIV
1764A F03
10
20 20s/DIV
1764A F06
Figure 3
Figure 6
0 5
VOUT = 2.5V IOUT = 1A WITH 1A PULSE COUT = 10F CERAMIC
0
VOUT = 2.5V ILOAD = 1A WITH 1A PULSE COUT = 100F CERAMIC
RESR (m)
RESR (m)
5
50mV/DIV
20mV/DIV
10 20
10
20 50 20s/DIV
1764A F04
20s/DIV
1764A F07
Figure 4
Figure 7
0
VOUT = 5V IOUT = 1A WITH 1A PULSE COUT = 10F CERAMIC
0
VOUT = 5V ILOAD = 1A WITH 1A PULSE COUT = 100F CERAMIC
RESR (m)
RESR (m)
5
5
50mV/DIV
20mV/DIV
10
10
20 20s/DIV
1764A F05
20 20s/DIV
1764A F08
Figure 5
Figure 8
A
RESR (m)
B
VOUT = 1.2V IOUT = 1A WITH 1A PULSE COUT = A = 10F CERAMIC B = 10F CERAMIC IN PARALLEL WITH 22F/ 45m POLY C = 10F CERAMIC IN PARALLEL WITH 100F/ 35m POLY
20mV/DIV
C
20s/DIV
1764A F09
Figure 9
1764afb
13
LT1764A Series
APPLICATIONS INFORMATION
Ceramic Capacitors Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior over temperature and applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 3 and 4. When used with a 5V regulator, a 10F Y5V capacitor can exhibit an effective value as low as 1F to 2F over the operating temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is available in higher values.
Table 2. PC Trace Resistors
10m 0.5oz CU 1.0oz CU 2.0oz CU Width Length Width Length Width Length 0.011" (0.28mm) 0.102" (2.6mm) 0.006" (0.15mm) 0.110" (2.8mm) 0.006" (0.15mm) 0.224" (5.7mm) 20m 0.011" (0.28mm) 0.204" (5.2mm) 0.006" (0.15mm) 0.220" (5.6mm) 0.006" (0.15mm) 0.450" (11.4mm) 30m 0.011" (0.28mm) 0.307" (7.8mm) 0.006" (0.15mm) 0.330" (8.4mm) 0.006" (0.15mm) 0.670" (17mm)
20 0 CHANGE IN VALUE (%)
BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F X5R
CHANGE IN VALUE (%)
-20 -40 -60 Y5V -80
-100
0
2
8 6 4 10 12 DC BIAS VOLTAGE (V)
14
16
1764 F10
Figure 3. Ceramic Capacitor DC Bias Characteristics
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Voltage and temperature coefficients are not the only sources of problems. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. "FREE" Resistance with PC Traces The resistance values shown in Table 1 can easily be made using a small section of PC trace in series with the output capacitor. The wide range of noncritical ESR makes it easy to use PC trace. The trace width should be sized to handle the RMS ripple current associated with the load. The output capacitor only sources or sinks current for a few microseconds during fast output current transitions. There
40 20 0 -20 -40 -60 -80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F 50 25 75 0 TEMPERATURE (C) 100 125
1764 F11
X5R
Y5V
-100 -50 -25
Figure 4. Ceramic Capacitor Temperature Characteristics
1764afb
LT1764A Series
APPLICATIONS INFORMATION
is no DC current in the output capacitor. Worst case ripple current will occur if the output load is a high frequency (>100kHz) square wave with a high peak value and fast edges (< 1s). Measured RMS value for this case is 0.5 times the peak-to-peak current change. Slower edges or lower frequency will significantly reduce the RMS ripple current in the capacitor. This resistor should be made using one of the inner layers of the PC board which are well defined. The resistivity is determined primarily by the sheet resistance of the copper laminate with no additional plating steps. Table 2 gives some sizes for 0.75A RMS current for various copper thicknesses. More detailed information regarding resistors made from PC traces can be found in Application Note 69, Appendix A. Overload Recovery Like many IC power regulators, the LT1764A-X has safe operating area protection. The safe area protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. The protection is designed to provide some output current at all values of input-to-output voltage up to the device breakdown. When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start up into very heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output currents. With a high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. Other regulators, such as the LT1085, also exhibit this phenomenon, so it is not unique to the LT1764A series. The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations are immediately after the removal of a short circuit or when the SHDN pin is pulled high after the input voltage has already been turned on. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable output operating points for the regulator. With this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. Output Voltage Noise The LT1764A regulators have been designed to provide low output voltage noise over the 10Hz to 100kHz bandwidth while operating at full load. Output voltage noise is typically 50nVHz over this frequency bandwidth for the LT1764A (adjustable version). For higher output voltages (generated by using a resistor divider), the output voltage noise will be gained up accordingly. This results in RMS noise over the 10Hz to 100kHz bandwidth of 15VRMS for the LT1764A increasing to 37VRMS for the LT1764A-3.3. Higher values of output voltage noise may be measured when care is not exercised with regards to circuit layout and testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the LT1764A-X. Power supply ripple rejection must also be considered; the LT1764A regulators do not have unlimited power supply rejection and will pass a small portion of the input noise through to the output. Thermal Considerations The power handling capability of the device is limited by the maximum rated junction temperature (125C). The power dissipated by the device is made up of two components: 1. Output current multiplied by the input/output voltage differential: (IOUT)(VIN - VOUT), and 2. GND pin current multiplied by the input voltage: (IGND)(VIN). The GND pin current can be found using the GND Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. The LT1764A series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum junction temperature rating of 125C must not be exceeded. It is important to give careful consideration to
1764afb
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15
LT1764A Series
APPLICATIONS INFORMATION
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. Surface mount heatsinks and plated through-holes can also be used to spread the heat generated by power devices. The following table lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 1/16" FR-4 board with one ounce copper.
Table 3. Q Package, 5-Lead DD
COPPER AREA TOPSIDE* 2500mm 1000mm 125mm
2 2
BACKSIDE 2500mm 2500mm 2500mm
2 2 2
BOARD AREA 2500mm 2500mm 2500mm
2 2 2
THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 23C/W 25C/W 33C/W
2
*Device is mounted on topside.
T Package, 5-Lead TO-220 Thermal Resistance (Junction-to-Case) = 2.5C/W
Calculating Junction Temperature Example: Given an output voltage of 3.3V, an input voltage range of 4V to 6V, an output current range of 0mA to 500mA 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) = 500mA VIN(MAX) = 6V IGND at (IOUT = 500mA, VIN = 6V) = 10mA So, P = 500mA(6V - 3.3V) + 10mA(6V) = 1.41W Using a DD package, the thermal resistance will be in the range of 23C/W to 33C/W depending on the copper area. So the junction temperature rise above ambient will be approximately equal to: 1.41W(28C/W) = 39.5C
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The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: TJMAX = 50C + 39.5C = 89.5C Protection Features The LT1764A regulators incorporate several protection features which make them 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 devices are 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 20V. Current flow into the device will be limited to less than 1mA and no negative voltage will appear at the output. The device will protect both itself and the load. This provides protection against batteries which can be plugged in backward. The output of the LT1764A-X 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. For fixed voltage versions, the output will act like a large resistor, typically 5k or higher, limiting current flow to typically less than 600A. For adjustable versions, 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 short-circuit current of the device and will protect itself by thermal limiting. In this case, grounding the SHDN pin will turn off the device and stop the output from sourcing the short-circuit current. The ADJ pin of the adjustable device can be pulled above or below ground by as much as 7V without damaging the device. If the input is left open circuit or grounded, the ADJ pin will act like an open circuit when pulled below ground and like a large resistor (typically 5k) in series with a diode when pulled above ground.
1764afb
LT1764A Series
APPLICATIONS INFORMATION
In situations where the ADJ pin is connected to a resistor divider that would pull the ADJ pin above its 7V clamp voltage if the output is pulled high, the ADJ pin input current must be limited to less than 5mA. For example, a resistor divider is used to provide a regulated 1.5V output from the 1.21V reference when the output is forced to 20V. The top resistor of the resistor divider must be chosen to limit the current into the ADJ pin to less than 5mA when the ADJ pin is at 7V. The 13V difference between OUT and ADJ pins divided by the 5mA maximum current into the ADJ pin yields a minimum top resistor value of 2.6k. 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 follow the curve shown in Figure 5. When the IN pin of the LT1764A-X is forced below the OUT pin or the OUT pin is pulled above the IN pin, input current will typically drop to less than 2A. This can happen if the input of the device is connected to a discharged (low voltage) battery and the output is held up by either a backup battery or a second regulator circuit. The state of the SHDN pin will have no effect on the reverse output current when the output is pulled above the input.
5.0
REVERSE OUTPUT CURRENT (mA)
TYPICAL APPLICATIO S
SCR Preregulator Provides Efficiency Over Line Variations
NTE5437 L2 10V AC AT 115VIN 10V AC AT 115VIN 12.1k* NTE5437 1N4002 "SYNC" 1N4002 TO ALL "V +" POINTS 2.4k 1N4002 V+ 1N4148 1k L1 500H LT1764A-3.3 VOUT 3.3V 3A 22F IN SHDN GND 34k* OUT FB
90V AC TO 140V AC
+
22F 750
L1: COILTRONICS CTX500-2-52 L2: STANCOR P-8560 *1% FILM RESISTOR V+
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4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0
LT1764A-1.5
LT1764A-1.8
LT1764A
TJ = 25C VIN = OV CURRENT FLOWS INTO OUTPUT PIN VOUT = VADJ (LT1764A) VOUT = VFB (LT1764A-1.5 LT1764A-1.8, LT1764A-2.5, LT1764A-3.3) LT1764A-2.5
LT1764A-3.3
1
2
345678 OUTPUT VOLTAGE (V)
9
10
1764 F12
Figure 5. Reverse Output Current
+
10000F
+
+
C1A 1/2 LT1018
1N4148
200k 0.1F
-
V+ 0.033F 750
+
C1B 1/2 LT1018 1N4148
V+
+
A1 LT1006 10k 10k V+
-
10k 1F
-
LT1004 1.2V
1764 TA03
1764afb
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LT1764A Series
TYPICAL APPLICATIO S
Adjustable Current Source
+
VIN > 2.7V
C2 3.3F
PACKAGE DESCRIPTION
Q Package 5-Lead Plastic DD Pak
(Reference LTC DWG # 05-08-1461)
0.256 (6.502)
0.060 (1.524)
0.060 (1.524) TYP
0.060 (1.524)
0.183 (4.648)
0.330 - 0.370 (8.382 - 9.398)
0.075 (1.905) 0.300 (7.620) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK +0.012 0.143 -0.020 0.067 (1.70) 0.028 - 0.038 BSC (0.711 - 0.965)
0.013 - 0.023 (0.330 - 0.584)
(
+0.305 3.632 -0.508
)
18
+
3
-
U
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R5 0.01 R1 1k R4 2.2k R6 2.2k IN OUT LT1764A-1.8 SHDN FB GND R8 100k
C1 10F
LT1004-1.2
LOAD
R2 40.2k R3 2k
C3 1F
R7 470
ADJUST R1 FOR 0A TO 3A CONSTANT CURRENT 2 8 1
1/2 LT1366 4
1764 TA04
0.390 - 0.415 (9.906 - 10.541) 15 TYP
0.165 - 0.180 (4.191 - 4.572)
0.045 - 0.055 (1.143 - 1.397) +0.008 0.004 -0.004
0.059 (1.499) TYP
(
+0.203 0.102 -0.102
)
0.095 - 0.115 (2.413 - 2.921) 0.050 0.012 (1.270 0.305)
Q(DD5) 1098
1764afb
LT1764A Series
PACKAGE DESCRIPTION
T Package 5-Lead Plastic TO-220 (Standard)
(Reference LTC DWG # 05-08-1421)
0.390 - 0.415 (9.906 - 10.541) 0.147 - 0.155 (3.734 - 3.937) DIA 0.230 - 0.270 (5.842 - 6.858) 0.460 - 0.500 (11.684 - 12.700) 0.570 - 0.620 (14.478 - 15.748) 0.330 - 0.370 (8.382 - 9.398) 0.700 - 0.728 (17.78 - 18.491) 0.620 (15.75) TYP 0.165 - 0.180 (4.191 - 4.572) 0.045 - 0.055 (1.143 - 1.397)
0.067 BSC (1.70)
0.028 - 0.038 (0.711 - 0.965)
3.58 (.141)
6.60 0.10 4.50 0.10
SEE NOTE 4
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 - 4.50* (.169 - .177)
0.09 - 0.20 (.0035 - .0079)
0.50 - 0.75 (.020 - .030)
NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE
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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SEATING PLANE 0.260 - 0.320 (6.60 - 8.13) 0.152 - 0.202 (3.861 - 5.131)
0.095 - 0.115 (2.413 - 2.921) 0.155 - 0.195* (3.937 - 4.953) 0.013 - 0.023 (0.330 - 0.584) * MEASURED AT THE SEATING PLANE
T5 (TO-220) 0399
0.135 - 0.165 (3.429 - 4.191)
FE Package 16-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation BB
4.90 - 5.10* (.193 - .201) 3.58 (.141) 16 1514 13 12 1110 9
2.94 (.116) 0.45 0.05 1.05 0.10 2.94 6.40 (.116) (.252) BSC
12345678
0.25 REF
1.10 (.0433) MAX
0 - 8
0.05 - 0.15 0.195 - 0.30 (.002 - .006) (.0077 - .0118) FE16 (BB) TSSOP 0204 TYP 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE
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0.65 (.0256) BSC
19
LT1764A Series
TYPICAL APPLICATIO U
Paralleling of Regulators for Higher Output Current
R1 0.01
+
VIN > 3.7V
C1 100F
IN OUT LT1764A-3.3 SHDN FB GND R2 0.01 IN OUT LT1764A ADJ GND
+
3.3V 6A C2 22F
R6 6.65k R7 4.12k
SHDN
SHDN
R3 2.2k
R4 2.2k
3
+ -
8 1 C3 0.01F
R5 1k
1/2 LT1366 2 4
1764 TA05
RELATED PARTS
PART NUMBER LT1120 LT1121 LT1129 LT1175 LT1374 LT1521 LT1529 LT1573 LT1575 LTC1735 LT1761 Series LT1762 Series LT1763 Series LT1962 LT1963A LT1964 DESCRIPTION 125mA Low Dropout Regulator with 20A IQ 150mA Micropower Low Dropout Regulator 700mA Micropower Low Dropout Regulator 500mA Negative Low Dropout Micropower Regulator 4.5A, 500kHz Step-Down Converter 300mA Low Dropout Micropower Regulator with Shutdown 3A Low Dropout Regulator with 50A IQ UltraFastTM Transient Response Low Dropout Regulator UltraFast Transient Response Low Dropout Regulator Synchronous Step-Down Converter 100mA, Low Noise, Low Dropout Micropower Regulators in SOT-23 150mA, Low Noise, LDO Micropower Regulators 500mA, Low Noise, LDO Micropower Regulators 300mA, Low Noise, LDO Micropower Regulator 1.5A, Low Noise, Fast Transient Response LDO 200mA, Low Noise, Negative LDO Micropower Regulator COMMENTS Includes 2.5V Reference and Comparator 30A IQ, SOT-223 Package 50A Quiescent Current 45A IQ, 0.26V Dropout Voltage, SOT-223 Package 4.5A, 0.07 Internal Switch, SO-8 Package 15A IQ, Reverse Battery Protection 500mV Dropout Voltage Drives External PNP Drives External N-Channel MOSFET High Efficiency, OPTI-LOOP(R) Compensation 20A Quiescent Current, 20VRMS Noise, ThinSOTTM Package 25A Quiescent Current, 20VRMS Noise, MSOP Package 30A Quiescent Current, 20VRMS Noise, SO-8 Package 20VRMS Noise, MSOP Package 40VRMS Noise, SOT-223 Package 30VRMS Noise, ThinSOT Package
OPTI-LOOP is a registered trademark of Linear Technology Corporation. UltraFast and ThinSOT are trademarks of Linear Technology Corporation.
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20
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
LT 0706 REV B * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2002

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