The switching frequency of 300kHz to 2.5MHz is set by the RT resistor connected between the RT-pin and AGND. The RT resistor must be selected between 12kΩ and 100kΩ according to Figure 6-1. If configured to use an external clock the device can synchronize the switching frequency to an external clock applied at the SYNCIN-pin. For single device configuration within ±50% of the set frequency by the RT-pin, in multi device configuration within ±25%. The internal clock is synchronized at the rising edge of the external clock signal applied at the SYNCIN-pin. The CFG1-pin Spread Spectrum setting is ignored during frequency synchronization and clock dithering is disabled.

The device always starts with the internal clock and starts synchronizing to an applied external clock during the START PHASE and the ACTIVE state (see ). The device synchronizes to the external clock as soon as the clock is applied and switches back to the internal clock in case the external clock stops.

Figure 6-1 Clock Synchronization