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LT1270A/LT1270 8A and 10A High Efficiency Switching Regulators
FEATURES
s s s s s s s s s
DESCRIPTIO
Wide Input Voltage Range: 3.5V to 30V Low Quiescent Current: 7mA Internal 8A Switch (10A for LT1270A) Very Few External Parts Required Self-Protected Against Overloads Shutdown Mode Draws Only 100A Supply Current Flyback-Regulated Mode Has Fully Floating Outputs Comes in Standard 5-Pin Package Can be Externally Synchronized (See LT1072 Data Sheet)
APPLICATI
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S
The LT1270A/LT1270 are monolithic high power switching regulators. Identical to the popular LT1070, except for switching frequency (60kHz) and higher switch current, they can be operated in all standard switching configurations including buck, boost, flyback, and inverting. A high current, high efficiency switch is included on the die along with all oscillator, control, and protection circuitry. Integration of all functions allows the LT1270A/LT1270 to be built in a standard TO-220 power package. This makes it extremely easy to use and provides "bust proof" operation similar to that obtained with 3-pin linear regulators. The LT1270A/LT1270 operate with supply voltages from 3.5V to 30V, and draw only 7mA quiescent current. By utilizing current-mode switching techniques, they provide excellent AC and DC load and line regulation. The LT1270A/LT1270 use adaptive anti-sat switch drive to allow very wide ranging load currents with no loss in efficiency. An externally activated shutdown mode reduces total supply current to 100A typical for standby operation.
High Efficiency Buck Converter PC Power Supply with Multiple Outputs Battery Upconverter Negative-to-Positive Converter
USER NOTE: This data sheet is only intended to provide specifications, graphs and a general functional description of the LT1270A/LT1270. Application circuits are included to show the capability of the LT1270A/LT1270. A complete design manual (AN-19) should be obtained to assist in developing new designs. AN-19 contains a comprehensive discussion of both the LT1070 and the external components used with it, as well as complete formulas for calculating the values of these components. AN-19 can also be used for the LT1270A/LT1270 by factoring in the higher switch current rating and higher operating frequency. A comprehensive CAD program called SwitcherCad is also available. Contact the local sales office in your area or the factory direct.
TYPICAL APPLICATI
VIN (8V TO 25V) 1N5819 VIN VSW LT1270*
High Efficiency Buck Converter
100
EFFICIENCY IS 88% @ 2A, 86% @ 5A. FOR POWER SHUTDOWN OPTION, CONSULT FACTORY. *THESE COMPONENTS RATED CONSERVATIVELY TO IMPROVE EFFICIENCY. MAXIMUM OUTPUT CURRENT CAN BE 7A. FOR HIGH EFFICIENCY, THE INDUCTOR SHOULD BE MOLYPERMALLOY OR FERRITE.
FB GND VC 0.047F 1k
OUTPUT POWER (W)
+
1F 0.047F 35H, 8A* 5V* 5A ANODE 9.1k
+
470F 35V
MBR1035* 2N3904 360
LT1431CZ REF CATHODE
10k
1N4158 560
1000F 25V
LT1270 * TA01
U
Maximum Output Power*
BOOST BUCK-BOOST, VO = 12V (INVERTING) FLYBACK 80 60 40 20 BUCK-BOOST, VO = 5V (INVERTING) 0 0 5 15 20 10 INPUT VOLTAGE (V) 25 30
LT1270 * TA02
UO
UO
*MULTIPLY BY 1.2 FOR LT1270A. BUCK MODE OUTPUT POWER (7.5A)(VOUT) TRANSFORMER TURNS RATIO MUST BE OPTIMUM TO ACHIEVE FULL POWER
1
LT1270A/LT1270 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
FRONT VIEW 5 4 3 2 1 T PACKAGE 5-LEAD TO-220 VIN VSW GND FB VC
Supply Voltage ....................................................... 30V Switch Output Voltage ............................................ 60V Feedback Pin Voltage (Transient, 1ms) ................ 15V Operating Junction Temperature Range LT1270AC/LT1270C (Oper.)................ 0C to 125C LT1270AC/LT1270C (Short-Ckt) ......... 0C to 140C Storage Temperature Range ................ - 65c to 150C Lead Temperature (Soldering, 10 sec)................ 300C
ORDER PART NUMBER LT1270CT LT1270ACT
TJMAX = 100C, JA = 2C/W, JA = 50C/ W
ELECTRICAL CHARACTERISTICS
SYMBOL VREF IB gm PARAMETER Reference Voltage Feedback Input Current Error Amplifier Transconductance Error Amplifier Source of Sink Current Error Amplifier Clamp Voltage Reference Voltage Line Regulation AV IQ Error Amplifier Voltage Gain Minimum Input Voltage Supply Current Control Pin Threshold Normal/Flyback Threshold on Feedback Pin VFB VFB Flyback Reference Voltage Change in Flyback Reference Voltage Flyback Reference Voltage Line Regulation Flyback Amplifier Transconductance (gm) Flyback Amplifier Source and Sink Current BV VSAT Output Switch Breakdown Voltage Output Switch ON Resistance (Note 1, 3) Control Voltage to Switch Current Transconductance IFB = 50A CONDITIONS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
MIN
q
TYP 1.244 1.244 350
MAX 1.264 1.274 750 1100 6000 7000 350 400 2.30 0.52 0.03
UNITS V V nA nA mho mho A A V V %/V V/V V mA V V V V V V %/V mho A A V
Measured at Feedback Pin VC = 0.8V VFB = VREF lC = 25A
1.224 1.214
q
3000 2400 150 120 1.80 0.25
4400 200
VC = 1.5V
q
Hi Clamp, VFB = 1V Lo Clamp, VFB = 1.5V 3V VIN VMAX, VC = 0.8V 0.9V VC 1.4V
q q
0.38 800 2.8 7
500
3.0 10 1.08 1.25 0.54 17.6 18.0 8.5 0.03 650 70 70
3V VIN VMAX, VC = 0.6V Duty Cycle = 0
q
0.80 0.60 0.40 15.0 14.0 4.5
0.90 0.45 16.3 6.8 0.01
q
0.05 IFB 1mA IFB = 50A 3V VIN VMAX lC = 10A VC = 0.6V Source IFB = 50A Sink 3V VIN VMAX ISW = 5mA TJ 100C TJ 125C
q q q
150 15 25 60
300 32 40 75 0.12 12
0.18 0.22
2
U
A/V
W
U
U
WW
W
LT1270A/LT1270
ELECTRICAL CHARACTERISTICS
SYMBOL ILIM ILIM IIN ISW f DCMAX PARAMETER Switch Current Limit (LT1270) (Note 3) Switch Current Limit (LT1270A) (Note 3) Supply Current Increase During Switch-ON Time Switching Frequency CONDITIONS
VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted.
MIN
q q q q
TYP
MAX 16 14 16.0 14.0
UNITS A A A A mA/A kHz kHz % s A mV mV
Duty Cycle = 50%, TJ 100C Duty Cycle = 80%, TJ 100C Duty Cycle = 50%, TJ 100C Duty Cycle = 80%, TJ 100C
8 6 10.0 7.5 25 50 50 80 60 92 1.5 100
40 70 70 95 400 250 300
q
Maximum Switch Duty Cycle Flyback Sense Delay Time Shutdown Mode Supply Current Shutdown Mode Threshold Voltage 3V VIN VMAX, VC = 0.05V 3V VIN VMAX
q
100 50
150
The q denotes specifications which apply over the full operating temperature range. Note 1: Measured with VC in Hi Clamp, VFB = 0.8V. Note 2: For duty cycles (DC) between 50% and 80%, minimum guaranteed
switch current is given by ILIM = 6.67 (1.7 - DC) for the LT1270 and ILIM = 8.33 (1.7 - DC) for the LT1270A. Note 3: Minimum current limit is reduced by 0.5A at 125C. 100C test limits are guaranteed by correlation to 125C tests.
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Current Limit vs Duty Cycle
2.4 1.6 TJ = 25C
SWITCH SATURATION VOLTAGE (V)
SWITCH CURRENT (A)
1.8 25C
-55C 1.2 125C 6
0
0
20
60 40 DUTY CYCLE (%)
UW
Switch Saturation Voltage
1.2
0.8
0.4
0 80 100
0
2
6 8 4 SWITCH CURRENT (A)
10
LT1270 * TA04
LT1270 * TA03
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 circuits as described herein will not infringe on existing patent rights.
3
LT1270A/LT1270
TYPICAL APPLICATIO S
Boost Converter (5V to 12V)
5V 55H* L1 55H** MBR1020 LT1270 10.7k FB GND VC 1k 1.24k 12V, 2A VIN VSW D1
VIN
VSW
+ 1000F
25V OPTIONAL INPUT FILTER L3
+
1F PULSE ENGINEERING #PE-92116
LT1270 * TA05
+
OPTIONAL INPUT FILTER L3 10H
C3 100F* FB GND VC C1 R3 R2 1.24k OPTIONAL OUTPUT FILTER L2 4F
VIN -20V
PACKAGE DESCRIPTIO
0.380 - 0.420 (9.652 - 10.668)
0.139 - 0.153 (3.531 - 3.886) DIA
0.560 - 0.650 (14.224 - 16.510) 0.866 - 0.913 (21.996 - 23.190)
0.057 - 0.077 (1.448 - 1.956)
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
U
U
Negative-to-Positive Buck-Boost Converter
L2 OPTIONAL OUTPUT FILTER C3
+
+
LT1270 C4 200F* FB GND VC R3 2.2k C1 0.22F
LT1270 * TA06
C2 2000F
R1 11.3k
VOUT 12V, 3A
1.24k *REQUIRED IF INPUT LEADS 2" **PULSE ENGINEERING #PE-92116
VIN -12V
Negative Buck Converter
+
VIN D1 L1 100H** VSW 12k C2 1000F R1 4.64k LOAD -5.2V, 7.5A
LT1270
+ C4
200F *REQUIRED IF INPUT LEADS 2" **PULSE ENGINEERING #PE-92115
LT1270 * TA07
Dimensions in inches (millimeters) unless otherwise noted.
0.079 - 0.135 (2.007 - 3.429)
0.169 - 0.185 (4.293 - 4.699)
0.035 - 0.055 (0.889 - 1.397)
0.460 - 0.500 (11.68 - 12.70)
0.620 0.020 (15.75 0.508) 0.700 - 0.728 (17.780 - 18.491)
0.970 - 1.050 (24.64 - 26.67) 0.055 - 0.090 (1.397 - 2.286) 0.079 - 0.115 (2.007 - 2.921) 0.170 - 0.185 (4.318 - 4.699)
T5 (FORMED) 0392
0.028 - 0.035 (0.711 - 0.889)
0.015 - 0.025 (0.381 - 0.635) 0.210 - 0.240 (5.334 - 6.096) 0.327 - 0.335 (8.306 - 8.509)
LT/GP 1292 5K REV B
(c) LINEAR TECHNOLOGY CORPORATION 1992

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