LM5025C Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Active Clamp Voltage Mode PWM Controller

LM5025C
April 23, 2009
Active Clamp Voltage Mode PWM Controller
General Description
The LM5025C is a functional variant of the LM5025 active
clamp PWM controller. The functional differences of the
LM5025C are: The maximum duty cycle of the LM5025C is
increased from 80% to 91%. The soft-start capacitor charging
current is increased from 20 µA to 90 µA. The V_CC regulator
current limit threshold is increased from 25 mA to 55 mA. The
CS1 and CS2 current limit thresholds have been increased to
0.5V. The internal CS2 filter discharge device has been dis-
abled and no longer operates each clock cycle. The internal
V_CC and V_REF regulators continue to operate when the line
UVLO pin is below threshold.
The LM5025C 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 designed for high-
speed operation including an oscillator frequency range up to
1MHz and total PWM and current sense propagation delays
less than 100 ns. The LM5025C 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, pre-
cision 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}
Packages
■ ^TSSOP-16
Typical Application Circuit
Simplified Active Clamp Forward Power Converter
30058901
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