SG6741A Ver la hoja de datos (PDF) - Fairchild Semiconductor

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SG6741A

Highly Integrated Green-Mode PWM Controller

Fairchild Semiconductor 

VDD Over-voltage Protection (OVP)

VDD over-voltage protection has been built in to prevent

damage due to abnormal conditions. Once the VDD

voltage is over the VDD over-voltage protection voltage

(VDD-OVP) and lasts for tD-VDDOVP, the PWM pulses are

disabled until the VDD voltage drops below the UVLO,

then starts again. Over-voltage conditions are usually

caused by open feedback loops.

Limited Power Control

The FB voltage increases every time the output of the

power supply is shorted or overloaded. If the FB voltage

remains higher than a built-in threshold for longer than

tD-OLP, PWM output is turned off. As PWM output is

turned off, the supply voltage VDD begins decreasing.

When VDD goes below the turn-off threshold (~10.5V)

the controller is totally shut down. VDD is charged up to

the turn-on threshold voltage of 16V through the startup

resistor until PWM output is restarted. This protection

feature continues as long as the overloading condition

persists. This prevents the power supply from

overheating due to overloading conditions.

Noise Immunity

Noise on the current sense or 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. Avoiding long PCB traces and

component leads, locating compensation and filter

components near the SG6741A, and increasing the

power MOS gate resistance improve performance.

© 2008 Fairchild Semiconductor Corporation

SG6741A • Rev. 1.0.1

9

www.fairchildsemi.com

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