LM5025B Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Active Clamp Voltage Mode PWM Controller

March 2006
LM5025B
Active Clamp Voltage Mode PWM Controller
General Description
The LM5025B is a functional variant of the LM5025 active
clamp PWM controller. The functional differences of the
LM5025B are as follows:
• The maximum PWM duty cycle is limited to less than
75% to reduce voltage stress on the power MOSFETs.
• The CS2 hiccup mode threshold is increased to 0.5V
• The CS2 filter discharge device is disabled
• The V_CC regulator continues to operate when the line
UVLO is below the threshold of normal operation
• The V_REF regulator is switched off when the line UVLO
input falls below the operating threshold
• The internal 5kΩ COMP pin pull-up resistor is removed
The LM5025B 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 LM5025B includes a high-voltage start-up regulator that
operates over a wide input range of 13V to 100V. Additional
features include: Line Under Voltage Lockout (UVLO), soft-
start, oscillator UP/DOWN sync capability, precision refer-
ence 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 maximum duty cycle clamp
n Programmable soft-start
n Current sense 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
20141101
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