LM5025A Datasheet, PDF(1/16 Page) National Semiconductor (TI) – Active Clamp Voltage Mode PWM Controller

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LM5025A Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Active Clamp Voltage Mode PWM Controller

December 2004

LM5025A

Active Clamp Voltage Mode PWM Controller

General Description

The LM5025A is a functional variant of the LM5025 active

clamp PWM controller. The functional differences of the

LM5025A are: The CS1 and CS2 current limit thresholds

have been increased to 0.5V. The internal CS2 filter dis-

charge device has been disabled and no longer operates

each clock cycle. The internal VCC and VREF regulators

continue to operate when the line UVLO pin is below thresh-

old.

The LM5025A PWM controller contains all of the features

necessary to implement power converters utilizing the Active

Clamp / Reset technique. With the active clamp technique,

higher efficiencies and greater power densities can be real-

ized compared to conventional catch winding or RDC clamp

/ reset techniques. Two control outputs are provided, the

main power switch control (OUT_A) and the active clamp

switch control (OUT_B). The two internal compound gate

drivers parallel both MOS and Bipolar devices, providing

superior gate drive characteristics. This controller is de-

signed for high-speed operation including an oscillator fre-

quency range up to 1MHz and total PWM and current sense

propagation delays less than 100ns. The LM5025A includes

a high-voltage start-up regulator that operates over a wide

input range of 13V to 90V. Additional features include: Line

Under Voltage Lockout (UVLO), softstart, oscillator UP/

DOWN sync capability, precision reference and thermal

shutdown.

Features

n Internal Start-up Bias Regulator

n 3A Compound Main Gate Driver

n Programmable Line Under-Voltage Lockout (UVLO) with

Adjustable Hysteresis

n Voltage Mode Control with Feed-Forward

n Adjustable Dual Mode Over-Current Protection

n Programmable Overlap or Deadtime between the Main

and Active Clamp Outputs

n Volt x Second Clamp

n Programmable Soft-start

n Leading Edge Blanking

n Single Resistor Programmable Oscillator

n Oscillator UP / DOWN Sync Capability

n Precision 5V Reference

n Thermal Shutdown

Packages

n TSSOP-16

n LLP-16 (5x5 mm) Thermally Enhanced

Typical Application Circuit

Simplified Active Clamp Forward Power Converter

20107401

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