Buck Pulse Width Modulator Stepdown Voltage Regulator

UC3578 is not recommended for new designs.
This product continues to be in production to support existing customers. Please consider one of these alternatives:
Similar but not functionally equivalent to the compared device:
LM2578A ACTIVE Switching Regulator Improve your design to achieve increased performance.

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  • Provides Simple Single Inductor Buck PWM Step-Down Voltage Regulation
  • Drives External High Side NMOS Switch
  • 14V to 72V Input Voltage Operating Range
  • Contains 100kHz Internal Oscillator, 2V Reference and UVLO
  • Soft Start on Power Up
  • Overcurrent Shutdown Followed by Soft Start
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The UC3578 is a PWM controller with an integrated high side floating gate driver. It is used in buck step down converters and regulates a positive output voltage. Intended to be used in a distributed power system, the IC allows operation from 14V to 72V input voltage which range includes the prevalent telecomm bus voltages. The output duty cycle of the UC3578 can vary between 0% and 90% for operation over the wide input voltage and load conditions.

The UC3578 simplifies the design of the single switch PWM buck converter by incorporating a floating high side driver for an external N-channel MOSFET switch. It also features a 100kHz fixed frequency oscillator, an internal 2V precision reference, an error amplifier configured for voltage mode operation, and a PWM comparator with latching logic. Complementing the traditional voltage mode control block, the UC3578 incorporates an overcurrent shutdown circuit with full cycle soft re-start to limit the input current to a user defined maximum value during overload operation. Additional functions include an under voltage lockout circuit to insure that sufficient input supply voltage is present before any switching activity can occur.

The UC2578 and the UC3578 are both available in surface mount and thru-hole power packages.

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Technical documentation

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* Datasheet Buck Pulse Width Modulator Stepdown Voltage Regulator datasheet Sep. 05, 1999
User guides UC3578 Telecom Buck Converter Reference Design Oct. 16, 2001

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