AN-6077

APPLICATION NOTE

© 2008 Fairchild Semiconductor Corporation

www.fairchildsemi.com

Rev. 1.0.2 • 12/1/08

6

Output Driver / Soft Driving

The output stage is a fast totem-pole gate driver capable of

directly driving an external MOSFET. An internal Zener

diode clamps the driver voltage under 18V to protect the

MOSFET against over-voltage. By integrating special

circuits to control the slew rate of switch-on rising time, the

switching noise, improving Electromagnetic Interference

(EMI) performance.

ON/OFF

Driver

18V

SG6742

GATE

Figure 13.

Gate Driver

Thermal Protection

RT pin. For over-temperature protection, an NTC thermistor

pin, is less than 1.05V; PWM output is latched off after a

If the thermal protection is not used, connect a small

capacitor (around 0.47nF is recommended) from the RT pin

to the GND pin to prevent noise interference. This RT

capacitor cannot be larger than 1nF or the thermal protection

is triggered before a successful startup of output voltage.

Over-Temperature Protection (OTP)

The built-in temperature-sensing circuit shuts down PWM

output once the junction temperature exceeds 135°C. While

startup threshold voltage of 15.5V through the startup

resistor until PWM output is restarted. This hiccup-mode

protection occurs repeatedly as long as the temperature

remains above 130°C. The temperature hysteresis window

for the OTP circuit is 25°C.