LT1074/LT1076 Step-Down Switching Regulator FEATURES ponents, are included on the chip. The topology is a classic positive “buck” configuration but several design innova- ■ 5A Onboard Switch (LT1074) tions allow this device to be used as a positive-to-negative ■ Operates Up to 60V Input converter, a negative boost converter, and as a flyback ■ 100kHz Switching Frequency converter. The switch output is specified to swing 40V ■ Greatly Improved Dynamic Behavior below ground, allowing the LT1074 to drive a tapped- ■ Available in Low Cost 5 and 7-Lead Packages inductor in the buck mode with output currents up to 10A. ■ Only 8.5mA Quiescent Current The LT1074 uses a true analog multiplier in the feedback ■ Programmable Current Limit loop. This makes the device respond nearly instanta- ■ Micropower Shutdown Mode neously to input voltage fluctuations and makes loop gain U independent of input voltage. As a result, dynamic behav- APPLICATIO S ior of the regulator is significantly improved over previous designs. ■ Buck Converter with Output Voltage Range of 2.5V to 50V On-chip pulse by pulse current limiting makes the LT1074 ■ Tapped-Inductor Buck Converter with 10A Output nearly bust-proof for output overloads or shorts. The input at 5V voltage range as a buck converter is 8V to 60V, but a self- ■ Positive-to-Negative Converter boot feature allows input voltages as low as 5V in the ■ Negative Boost Converter inverting and boost configurations. ■ Multiple Output Buck Converter The LT1074 is available in low cost TO-220 or DD packages U with frequency pre-set at 100kHz and current limit at 6.5A DESCRIPTIO (LT1076 = 2.6A). A 7-pin TO-220 package is also available which allows current limit to be adjusted down to zero. In The LT®1074 is a 5A (LT1076 is rated at 2A) monolithic addition, full micropower shutdown can be programmed. bipolar switching regulator which requires only a few See Application Note 44 for design details. external parts for normal operation. The power switch, all A fixed 5V output, 2A version is also available. See LT1076-5. oscillator and control circuitry, and all current limit com- , LTC and LT are registered trademarks of Linear Technology Corporation. UTYPICAL APPLICATIOBuck Converter EfficiencyBasic Positive Buck Converter LT1074 100 L1** 50µH (LT1074) V = 12V, V = 20V OUT IN 100µH (LT1076) 90 5V V V IN SW 5A 10V TO 40V * USE MBR340 FOR LT1076 ** COILTRONICS #50-2-52 (LT1074) 80 LT1074 R1 MBR745* 2.8k #100-1-52 (LT1076) V = 5V, V = 15V OUT IN 1% PULSE ENGINEERING, INC. EFFICIENCY (%) FB 70 GND V #PE-92114 (LT1074) C #PE-92102 (LT1076) R2 R3 60 L = 50µH TYPE 52 CORE 2.21k HURRICANE #HL-AK147QQ (LT1074) 2.7k DIODE = MBR735 + 1% + #HL-AG210LL (LT1076) C3† C2 C1 † RIPPLE CURRENT RATING ≥ IOUT/2 50 200µF 0.01µF 500µF 0 1 2 3 4 5 6 25V OUTPUT LOAD CURRENT (A) LT1074•TA01 LT1074•TPC27 sn1074 1074fds 1
