© 2008 Fairchild Semiconductor Corporation

www.fairchildsemi.com

SG6846G • Rev. 1.0.0

3

Marking Information

Figure 3. Top Mark

Pin Configuration

Figure 4. Pin Configuration

Pin Definitions

Pin #

Name

Function

Description

1

GND

Ground

Ground.

2

FB

Feedback

The signal from the external compensation circuit is fed into this pin. The

PWM duty cycle is determined in response to the signal from this pin and the

current-sense signal from pin 6.

3

VIN

Line-voltage

Detection

Line-voltage detection is used for brownout protection with hysteresis.

Constant output power limit over universal AC input range is also achieved

using this pin. Add a low-pass filter to filter out line ripple on the bulk capacitor.

4

RI

Reference

Setting

A resistor from the RI pin to ground generates a reference current source that

determines the switching frequency. Increasing the resistance reduces the

switching frequency. Using a 26kΩ resistor results in a 65kHz switching

frequency.

5

RT

Temperature

Detection

For over-temperature protection, an external NTC thermistor is connected

from this pin to the GND pin. The impedance of the NTC decreases at high

temperatures. Once the voltage of the RT pin drops below a threshold, PWM

output is disabled.

6

SENSE

Current Sense

Current sense. The sensed voltage is used for peak-current-mode control and

cycle-by-cycle current limiting. If the switching current is higher than OCP

threshold and lasts for 110ms, SG6846G turns off immediately. This two-level

OCP feature is especially suitable for SMPS with surge current output.

7

VDD

Power Supply

Power supply. If an open-circuit failure occurs in the feedback loop, the

threshold.

8

GATE

Driver Output

The totem-pole output driver for the power MOSFET. It is internally clamped

below 18V.