The RT/SYNC pin can be used to sync

The RT/SYNC pin can be used to synchronize the device’s internal oscillator to an external system clock. The external clock should be coupled to the RT/SYNC pin through a 47pF capacitor, as shown in Figure 1. The external clock logic-high level should be higher than 3V, logic-low level lower than 0.5V and the duty cycle of the external clock should be in the range of 10% to 70%. External clock-synchronization is allowed only in PWM mode of operation (MODE pin connected to GND). The RT resistor should be selected to set the switching frequency 10% lower than the external clock frequency. The external clock should be applied at least 500μs after enabling the device for proper configuration of the internal loop compensation.