7.3.7 Synchronization (SYNC/MODE)

The LMZM33604 switching frequency can also be synchronized to an external clock from 350 kHz to 2.2 MHz. Before the external clock is present, the device switches at the frequency programmed by the R_RT resistor. Select R_RT to set the frequency to be the same as the external synchronization frequency. Once the external clock is present, the device transitions to SYNC mode within 1 ms (typical) and overrides the RT mode. If the external clock is removed, the device continues to switch at the SYNC frequency for 10 µs (typ) before returning to the switching frequency set by the RT resistor, resulting in minimal disturbance to the output voltage during the transitions.

Recommendations for the external clock include a high level no lower than 2 V, low level no higher than 0.4 V, duty cycle between 10% and 90%, and both positive and negative pulse width no shorter than 80 ns.

When synchronizing to an external clock, the device operation mode is FPWM. If synchronization is not needed, connect this pin to AGND or logic high to select either Auto mode or FPWM mode. Do not leave this pin open.

The synchronization frequency must be selected based on the output voltages of the devices being synchronized. Table 6 and show the allowable frequencies for a given range of output voltages. For the most efficient solution, always select the lowest allowable frequency.