August 2005
LM5026
Active Clamp Current Mode PWM Controller
General Description
Features
n Current Mode Control
The LM5026 PWM controller contains all of the features
necessary to implement power converters utilizing the active
clamp / reset technique with current mode control. 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
device can be configured to control either a P-Channel or
N-Channel clamp switch. The main gate driver features a
compound configuration, consisting of both MOS
and Bipolar devices, providing superior gate drive character-
istics. The LM5026 can be configured to operate with bias
voltages over a wide input range of 8V to 100V. Additional
features include programmable maximum duty cycle, line
under-voltage lockout, cycle-by-cycle current limit, hiccup
mode fault operation with adjustable timeout delay, PWM
slope compensation, soft-start, 1MHz capable oscillator with
synchronization input / output capability, precision reference
and thermal shutdown.
n Internal 100V Start-up Bias Regulator
n 3A Compound Main Gate Driver
n High Bandwidth Opto-coupler Interface
n Programmable Line Under-Voltage Lockout (UVLO) with
Adjustable Hysteresis
n Versatile Dual Mode Over-Current Protection with hiccup
delay timer
n Programmable Overlap or Deadtime between the Main
and Active Clamp Outputs
n Programmable Maximum Duty Cycle Clamp
n Programmable Soft-start
n Leading Edge Blanking
n Resistor Programmed 1MHz Capable Oscillator
n Oscillator Sync I/O Capability
n Precision 5V Reference
Packages
n TSSOP-16
n LLP-16 (5x5 mm) Thermally Enhanced (Available
Soon)
Typical Application Circuit
20147901
Simplified Forward Power Converter with Active Clamp Reset
© 2005 National Semiconductor Corporation
DS201479
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