The LMZM33602 switching frequency can also be synchronized to an external clock from 200 kHz to 1.2 MHz. To implement the synchronization feature, couple an AC signal to the EN/SYNC pin (pin 2) with a peak-to-peak amplitude of at least 2.8 V, not to exceed 5.5 V. The minimum SYNC clock ON and OFF time must be longer than 100ns. The AC signal must be coupled through a small capacitor (1 nF) as shown in Figure 7-8. R_ENT is required for this synchronization circuit, but R_ENB is not required if an external UVLO adjustment is not needed.

Before the external clock is present, or when a valid clock signal is removed, the device works in RT mode and the switching frequency is set by R_RT resistor. Select R_RT so that it sets the frequency close to the external synchronization frequency. When the external clock is present, the SYNC mode overrides the RT mode.

The synchronization frequency must be selected based on the output voltages of the devices being synchronized. Table 7-3 shows the allowable frequencies for a given range of output voltages. For the most efficient solution, always select the lowest allowable frequency.

Figure 7-8 AC Coupled SYNC Signal