LT1270

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 100µA Supply Current Flyback-Regulated Mode Has Fully Floating Outputs Comes in Standard 5-Pin Package Can be Externally Synchronized (See LT1072 Data Sheet) APPLICATI s s s s 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 100µA 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 µPOWER 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 0.047µF 1k OUTPUT POWER (W) + 1µF 0.047µF 35µH, 8A* 9.1k 5V* 5A ANODE + 470µF 35V MBR1035* 2N3904 360Ω LT1431CZ REF CATHODE 10k 1N4158 560Ω 1000µF 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.)................ 0°C to 125°C LT1270AC/LT1270C (Short-Ckt) ......... 0°C to 140°C Storage Temperature Range ................ – 65°c to 150°C Lead Temperature (Soldering, 10 sec)................ 300°C ORDER PART NUMBER LT1270CT LT1270ACT TJMAX = 100°C, θJA = 2°C/W, θJA = 50°C/ 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 = 50µA 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 µmho µmho µA µA V V %/V V/V V mA V V V V V V %/V µmho µA µA V Measured at Feedback Pin VC = 0.8V VFB = VREF ∆lC = ± 25µA 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 = 50µA 3V ≤ VIN ≤ VMAX ∆lC = ± 10µA VC = 0.6V Source IFB = 50µA Sink 3V ≤ VIN ≤ VMAX ISW = 5mA TJ ≤ 100°C TJ ≤ 125°C q q q 150 15 25 60 300 32 40 75 0.12 12 0.18 0.22 2 U Ω Ω 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 % µs µA mV mV Duty Cycle = 50%, TJ ≤ 100°C Duty Cycle = 80%, TJ ≤ 100°C Duty Cycle = 50%, TJ ≤ 100°C Duty Cycle = 80%, TJ ≤ 100°C 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 125°C. 100°C test limits are guaranteed by correlation to 125°C tests. TYPICAL PERFOR A CE CHARACTERISTICS Switch Current Limit vs Duty Cycle 2.4 1.6 TJ = 25°C SWITCH SATURATION VOLTAGE (V) SWITCH CURRENT (A) 1.8 25°C –55°C 1.2 125°C 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 55µH* L1 55µH** MBR1020 LT1270 10.7k FB GND VC 1k 1.24k 12V, 2A VIN VSW D1 VIN VSW + 1000µF 25V OPTIONAL INPUT FILTER L3 + 1µF LT1270 • TA05 PULSE ENGINEERING #PE-92116 + OPTIONAL INPUT FILTER L3 10µH C3 100µF* GND VC 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 200µF* GND VC R3 2.2k C1 0.22µF LT1270 • TA06 C2 2000µF R1 11.3k VOUT 12V, 3A FB 1.24k *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING #PE-92116 VIN –12V Negative Buck Converter + VIN D1 L1 100µH** VSW 12k C2 1000µF R1 4.64k LOAD –5.2V, 7.5A LT1270 FB C1 R3 LT1270 • TA07 R2 1.24k OPTIONAL OUTPUT FILTER L2 4µF + C4 200µF *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING #PE-92115 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 © LINEAR TECHNOLOGY CORPORATION 1992