It is often desirable to synchronize the operation of multiple regulators in a single system, resulting in a well-defined system level performance. The select variants in the LMR36503-Q1 with the MODE/SYNC pin allow the power designer to synchronize the device to a common external clock. The LMR36503-Q1 implements an in-phase locking scheme, where the rising edge of the clock signal, provided to the MODE/SYNC pin of the LMR36503-Q1, corresponds to the turning on of the high-side device. The external clock synchronization is implemented using a phase locked loop (PLL) eliminating any large glitches. The external clock fed into the LMR36503-Q1 replaces the internal free-running clock, but does not affect any frequency foldback operation. Output voltage continues to be well-regulated. The device remains in FPWM mode and operates in CCM for light loads when synchronization input is provided.

The MODE/SYNC input pin in the LMR36503-Q1 can operate in one of three selectable modes:

• Auto Mode: Pulse frequency modulation (PFM) operation is enabled during light load and diode emulation prevents reverse current through the inductor. See Section 8.4.3.2 for more details.
• FPWM Mode: In FPWM mode, diode emulation is disabled, allowing current to flow backwards through the inductor. This allows operation at full frequency even without load current. See Section 8.4.3.3 for more details.
• SYNC Mode: The internal clock locks to an external signal applied to the MODE/SYNC pin. As long as output voltage can be regulated at full frequency and is not limited by minimum off-time or minimum on-time, clock frequency is matched to the frequency of the signal applied to the MODE/SYNC pin. While the device is in SYNC mode, it operates as though in FPWM mode: diode emulation is disabled allowing the frequency applied to the MODE/SYNC pin to be matched without a load.