Step-Down Switching Regulator

The LT1074 is a 5A (LT1076 is rated at 2A) monolithic bipolar switching regulator which requires only a few external parts for normal operation. The power switch, all oscillator and control circuitry, and all current limit components,are included on the chip. The topology is a classic positive “buck” configuration but several design innovations allow this device to be used as a positive-to-negative converter, a negative boost converter, and as a flyback converter. The switch output is specified to swing 40V below ground, allowing the LT1074 to drive a tapped-inductor in the buck mode with output currents up to 10A.

The LT1074 uses a true analog multiplier in the feedback loop. This makes the device respond nearly instantaneously to input voltage fluctuations and makes loop gain independent of input voltage. As a result, dynamic behavior of the regulator is significantly improved over previous designs.

On-chip pulse by pulse current limiting makes the LT1074 nearly bust-proof for output overloads or shorts. The input voltage range as a buck converter is 8V to 60V, but a self-boot feature allows input voltages as low as 5V in the inverting and boost configurations.

The LT1074 is available in lowcost TO-220 or DD packages with frequency pre-set at 100kHz and current limit at 6.5A (LT1076 =2.6A). A 7-pin TO-220 package is also available which allows current limit to be adjusted down to zero. In addition, full micropower shutdown can be programmed. See Application Note 44 for design details.

A fixed 5V output, 2A version is also available. See LT1076-5.

Applications

* Buck Converter with Output Voltage Range of 2.5V to 50V

* Tapped-Inductor Buck Converter with 10A Output at 5V

* Positive-to-Negative Converter

* Negative Boost Converter

* Multiple Output Buck Converter

* 5A Onboard Switch (LT1074)

* Operates Up to 60V Input

* 100kHz Switching Frequency

* Greatly Improved Dynamic Behavior

* Available in Low Cost 5 and 7-Lead Packages

* Only 8.5mA Quiescent Current

* Programmable Current Limit

* Micropower Shutdown Mode