FAN400ANY Ver la hoja de datos (PDF) - Fairchild Semiconductor

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FAN400ANY

Low-Power Green-Mode PWM Flyback Power Controller without Secondary Feedback

Fairchild Semiconductor 

Operation Description (Continued)

Slope Compensation

The sensed voltage across the current sense resistor is

used for current mode control and pulse-by-pulse

current limiting. The built-in slope compensation

improves power supply stability. Furthermore, it

prevents sub-harmonic oscillations that normally would

occur because of peak current mode control. A

positively sloped, synchronized ramp is activated with

every switching cycle. The slope of the ramp is:

0.33 × Duty

(1)

Duty(max.)

Noise Immunity

Noise from the current sense or the control signal may

cause significant pulse-width jitter, particularly in

continuous-conduction mode. Slope compensation

helps alleviate this problem. Good placement and

layout practices should be followed. The designer

should avoid long PCB traces and component leads.

Compensation and filter components should be located

near the FAN400A. Finally, increasing the power-MOS

gate resistance is advised.

© 2008 Fairchild Semiconductor Corporation

FAN400A Rev. 1.0.1

10

www.fairchildsemi.com

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