7.4.4 Slave Mode and SYNCOUT

The LM5122ZA is designed to easily implement dual (or higher) phase boost converters by configuring one controller as a master and all others as slaves. Slave mode is activated by connecting the FB pin to the VCC pin. The FB pin is sampled during initial power-on and if a slave configuration is detected, the state is latched. In the slave mode, the error amplifier is disabled and has a high impedance output, 10-μA hiccup-mode off-time charging current and 5-μA hiccup-mode off-time discharging current are disabled, 5-μA normal-state RES discharging current and 10-μA soft-start charging current are disabled, 30 μA fault-state RES charging current is changed to 35 μA. 10-μA UVLO hysteresis current source works the same as master mode. Also, in slave mode, the internal oscillator is disabled, and an external synchronization clock is required.

The SYNCOUT function provides a 180° phase shifted clock output, enabling easy dual-phase interleaved configuration. By directly connecting master1 SYNCOUT to slave1 SYNCIN, the switching frequency of slave controller is synchronized to the master controller with 180º phase shift. In master mode, if OPT pin is tied to GND, an internal oscillator clock divided by two with 50% duty cycle is provided to achieve an 180º phase-shifted operation in two phase interleaved configuration. Switching frequency of master controller is half of the external clock frequency with this configuration. If the OPT pin voltage is higher than 2.7-V OPT threshold or the pin is tied to VCC, SYNCOUT is disabled and the switching frequency of master controller becomes the same as the external clock frequency. An external synchronization clock should be always provided and directly connected to SYNCIN for master2, slave1 and slave2 configurations. See Interleaved Boost Configuration for detailed information.