LT1176/LT1176-5

Step-Down Switching Regulator

FEATURES

■ 1.2A On-Board Switch

■ 100kHz Switching Frequency

■ Excellent Dynamic Behavior

■ DIP and Surface Mount Packages

■ Only 8mA Quiescent Current

■ Preset 5V Output Available

■ Operates Up to 35V Input

■ Micropower Shutdown Mode

APPLICATION

■ Buck Converter with Output Voltage Range of 2.5V to 30V

■ Positive-to-Negative Converter

■ Negative Boost Converter

■ Mulitple Output Buck Converter

DESCRIPTION

The LT1176 is a 1A 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 allows 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 below ground.

The LT1176 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 LT1176 nearly bust-proof for output overloads or shorts. The input voltage range as a buck converter is 8V to 35V, but a selfboot feature allows input voltages as low as 5V in the inverting and boost configurations.

The LT1176 is available in a low cost 8-lead DIP package with frequency preset at 100kHz and current limit at 1.7A An adjustable output is offered as well as a preset 5V version. For further design details and application help, see the LT1074/LT1076 data sheet and Application Note 44.

ABSOLUTE MAXMUM RATINGS

Input Voltage .......................................................... 38V

Switch Voltage With Respect to Input Voltage........ 50V

Switch Voltage With Respect to Ground Pin

(V_SW Negative) (Note 6) ......................................... 20V

Feedback Pin Voltage.......................................– 2V, 10V

Shutdown Pin Voltage (Not to Exceed VIN) ............. 35V

Status Pin Voltage

(Current Must Be Limited to 5mA When Status Pin

Switches “ON”) ................................................... 30V

I_LIM Pin Voltage (Forced)...................................... 5.5V

Maximum Operating Ambient Temperature Range

LT1176C/LT1176C-5 .............................. 0°C to 70°C

Maximum Operating Junction Temperature Range

LT1176C/LT1176C-5 ............................ 0°C to 125°C

Storage Temperature Range ................ – 65°C to 150°C

Lead Temperature (Soldering, 10 sec) ............... 300°C

TYPICAL APPLICATION

Basic 5V Positive Buck Converter 5V Buck Converter Efficiency

PACKAGE/ORDER INFORMATION

BLOCK DIAGRAM

PACKAGE DESCRIPTION Dimensions in inches (milimeters) unless otherwise noted.

N Package 8-Lead Plastic DIP