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Active Clamp Voltage Mode PWM Controller from the PowerWise® Family
National Semiconductor

Description
The LM5025 PWM controller contains all of the features necessary to implement power converters utilizing the Active Clamp / Reset technique. The device can be configured to control either a P-Channel clamp switch or an N-Channel clamp switch. With the active clamp technique, higher efficiencies and greater power densities can be realized 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 active clamp output can be configured for either a guaranteed overlap time (for P-Channel switch applications) or a guaranteed deadtime (for N_Channel applications). The two internal compound gate drivers parallel both MOS and Bipolar devices, providing superior gate drive characteristics. This controller is designed for high-speed operation including an oscillator frequency range up to 1MHz and total PWM and current sense propagation delays less than 100ns. The LM5025 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

 • Internal Start-up Bias Regulator
 • 3A Compound Main Gate Driver
 • Programmable Line Under-Voltage Lockout (UVLO) with Adjustable Hysteresis
 • Voltage Mode Control with Feed-Forward
 • Adjustable Dual Mode Over-Current Protection
 • Programmable Overlap or Deadtime between the Main and Active Clamp Outputs
 • Volt x Second Clamp
 • Programmable Soft-start
 • Leading Edge Blanking
 • Single Resistor Programmable Oscillator
 • Oscillator UP / DOWN Sync Capability
 • Precision 5V Reference
 • Thermal Shutdown




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