This pin is bidirectional (refer to Figure 11). When used as an output, SYNC is used as a clock, which is the same as the internal clock of the device. When used as an input, SYNC overrides the internal oscillator of the chip and acts as the clock signal. This bidirectional feature allows synchronization of multiple power supplies. Also, the SYNC signal internally discharge the CT capacitor and any filter capacitors that are present on the RAMP pin. The internal SYNC circuitry is level sensitive, with an input-low threshold of 1.9 V, and an input-high threshold of 2.1 V. A resistor as small as 3.9 kΩ may be tied between SYNC and GND to reduce the sync pulse width.