ZHCSJY0B June 2012 – June 2019 LMR12015 , LMR12020
PRODUCTION DATA.
The LMR12015/20 switching frequency can be synchronized to an external clock, between 1.00 and 2.35 MHz, applied at the SYNC pin. At the first rising edge applied to the SYNC pin, the internal oscillator is overridden and subsequent positive edges will initiate switching cycles. If the external SYNC signal is lost during operation, the LMR12015/20 reverts to its internal 2-MHz oscillator within 1.5 µs. To disable frequency synchronization and utilize the internal 2-MHz oscillator, connect the SYNC pin to GND.
The SYNC pin gives the designer the flexibility to optimize their design. A lower switching frequency can be chosen for higher efficiency. A higher switching frequency can be chosen to keep EMI out of sensitive ranges such as the AM radio band. Synchronization can also be used to eliminate beat frequencies generated by the interaction of multiple switching power converters. Synchronizing multiple switching power converters will result in cleaner power rails.
The selected switching frequency (fSYNC) and the minimum on-time (tMIN) limit the minimum duty cycle (DMIN) of the device.
Operation below DMIN is not reccomended. The LMR12015/20 skips pulses to keep the output voltage in regulation, and the current limit is not ensured. The switching is in phase but no longer at the same switching frequency as the SYNC signal.