LT1270A/LT1270 8A and 10A High Efficiency Switching Regulators U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ 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) 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. UO APPLICATI ■ ■ ■ ■ S 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. High Efficiency Buck Converter PC Power Supply with Multiple Outputs Battery Upconverter Negative-to-Positive Converter 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. 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. UO TYPICAL APPLICATI Maximum Output Power* 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. BOOST † VSW 1N5819 LT1270* VIN FB GND VC + 1µF 0.047µF 0.047µF 1k 35µH, 8A* 5V* 5A ANODE + 470µF 35V LT1431CZ REF CATHODE MBR1035* 1N4158 560Ω 60 FLYBACK† 40 BUCK-BOOST, VO = 5V (INVERTING) 20 9.1k 0 0 10k 2N3904 360Ω BUCK-BOOST, VO = 12V (INVERTING) 80 OUTPUT POWER (W) VIN (8V TO 25V) 5 15 20 10 INPUT VOLTAGE (V) 25 30 LT1270 • TA02 1000µF 25V LT1270 • TA01 *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 PACKAGE/ORDER I FOR ATIO U W W W 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 ELECTRICAL CHARACTERISTICS PARAMETER CONDITIONS VREF Reference Voltage Measured at Feedback Pin VC = 0.8V IB Feedback Input Current VFB = VREF gm Error Amplifier Transconductance ∆lC = ±25µA Error Amplifier Source of Sink Current VC = 1.5V Error Amplifier Clamp Voltage Hi Clamp, VFB = 1V Lo Clamp, VFB = 1.5V Reference Voltage Line Regulation 3V ≤ VIN ≤ VMAX, VC = 0.8V Error Amplifier Voltage Gain 0.9V ≤ VC ≤ 1.4V Minimum Input Voltage IQ FRONT VIEW 5 4 3 2 1 TJMAX = 100°C, θJA = 2°C/W, θJA = 50°C/ W ● MIN TYP MAX UNITS 1.224 1.214 1.244 1.244 1.264 1.274 V V 350 750 1100 nA nA 3000 2400 4400 ● 6000 7000 µmho µmho 150 120 200 ● 350 400 µA µA 2.30 0.52 V V 0.03 %/V 1.80 0.25 3V ≤ VIN ≤ VMAX, VC = 0.6V Control Pin Threshold Duty Cycle = 0 0.38 ● 500 Normal/Flyback Threshold on Feedback Pin IFB = 50µA ● 800 2.8 ● Supply Current Flyback Reference Voltage mA 7 10 1.08 1.25 V V 0.40 0.45 0.54 V 15.0 14.0 16.3 17.6 18.0 V V 4.5 6.8 8.5 V 0.01 0.03 %/V 150 300 650 µmho 70 70 µA µA Flyback Reference Voltage Line Regulation IFB = 50µA 3V ≤ VIN ≤ VMAX Flyback Amplifier Transconductance (gm) ∆lC = ±10µA Flyback Amplifier Source and Sink Current VC = 0.6V Source IFB = 50µA Sink ● ● 15 25 32 40 BV Output Switch Breakdown Voltage 3V ≤ VIN ≤ VMAX ISW = 5mA ● 60 75 VSAT Output Switch ON Resistance (Note 1, 3) TJ ≤ 100°C TJ ≤ 125°C 2 V 0.90 0.05 ≤ IFB ≤ 1mA Control Voltage to Switch Current Transconductance V/V 3.0 0.80 0.60 Change in Flyback Reference Voltage VFB LT1270CT LT1270ACT T PACKAGE 5-LEAD TO-220 ● VFB VIN VSW GND FB VC ORDER PART NUMBER VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted. SYMBOL AV U RATI GS W AXI U U ABSOLUTE 0.12 12 V 0.18 0.22 Ω Ω A/V LT1270A/LT1270 ELECTRICAL CHARACTERISTICS VIN = 15V, VC = 0.5V, VFB = VREF, switch pin open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN ILIM Switch Current Limit (LT1270) (Note 3) Duty Cycle = 50%, TJ ≤ 100°C Duty Cycle = 80%, TJ ≤ 100°C ● ● 8 6 16 14 A A ILIM Switch Current Limit (LT1270A) (Note 3) Duty Cycle = 50%, TJ ≤ 100°C Duty Cycle = 80%, TJ ≤ 100°C ● ● 10.0 7.5 16.0 14.0 A A ∆IIN ∆ISW Supply Current Increase During Switch-ON Time f Switching Frequency ● DCMAX Maximum Switch Duty Cycle TYP MAX 25 40 mA/A 50 50 60 70 70 kHz kHz 80 92 95 % 100 400 µA 150 250 300 mV mV Flyback Sense Delay Time µs 1.5 Shutdown Mode Supply Current 3V ≤ VIN ≤ VMAX, VC = 0.05V Shutdown Mode Threshold Voltage 3V ≤ VIN ≤ VMAX 100 50 ● The ● 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 UNITS 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. U W TYPICAL PERFOR A CE CHARACTERISTICS Switch Saturation Voltage Switch Current Limit vs Duty Cycle 1.6 2.4 SWITCH SATURATION VOLTAGE (V) SWITCH CURRENT (A) TJ = 25°C 1.8 –55°C 25°C 1.2 125°C 6 0 1.2 0.8 0.4 0 0 20 60 40 DUTY CYCLE (%) 80 100 0 2 6 8 4 SWITCH CURRENT (A) 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. 10 LT1270 • TA04 3 LT1270A/LT1270 U TYPICAL APPLICATIO S Negative-to-Positive Buck-Boost Converter Boost Converter (5V to 12V) 5V L2 55µH* VIN OPTIONAL OUTPUT FILTER L1 55µH** VSW MBR1020 D1 VIN 12V, 2A LT1270 VSW + 10.7k FB GND + 1000µF VC + 25V 1k 1.24k OPTIONAL INPUT FILTER + 1µF LT1270 VOUT 12V, 3A R1 11.3k C2 2000µF C4 200µF* FB VC GND R3 2.2k C1 0.22µF L3 PULSE ENGINEERING #PE-92116 C3 LT1270 • TA05 VIN –12V 1.24k *REQUIRED IF INPUT LEADS ≥ 2" **PULSE ENGINEERING #PE-92116 LT1270 • TA06 Negative Buck Converter + VIN + OPTIONAL INPUT FILTER L3 10µH D1 L1 100µH** C2 1000µF –5.2V, 7.5A VSW 12k LT1270 C3 100µF* FB VC GND C1 R2 1.24k R3 VIN –20V OPTIONAL OUTPUT FILTER L2 4µF LT1270 • TA07 U PACKAGE DESCRIPTIO 0.380 – 0.420 (9.652 – 10.668) R1 4.64k LOAD + 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) 0.139 – 0.153 (3.531 – 3.886) DIA 0.560 – 0.650 (14.224 – 16.510) 0.169 – 0.185 (4.293 – 4.699) 0.460 – 0.500 (11.68 – 12.70) 0.866 – 0.913 (21.996 – 23.190) 0.035 – 0.055 (0.889 – 1.397) 0.620 ± 0.020 (15.75 ± 0.508) 0.700 – 0.728 (17.780 – 18.491) 0.970 – 1.050 (24.64 – 26.67) 0.057 – 0.077 (1.448 – 1.956) 4 0.028 – 0.035 (0.711 – 0.889) Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 0.015 – 0.025 (0.381 – 0.635) 0.210 – 0.240 (5.334 – 6.096) 0.327 – 0.335 (8.306 – 8.509) 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 LT/GP 1292 5K REV B LINEAR TECHNOLOGY CORPORATION 1992