The nSTRT (push button input) serves as an external initialization input to the PMIC. nSTRT is internally pulled up to SVIN and monitored. When the nSTRT is pulled/detected LOW (SW3 pressed), the MCP16502 initiates the turn-on sequence.
The nSTRTO signal is asserted LOW whenever the nSTRT is detected to be LOW, and it is high-Z otherwise (nSTRTO has an external pull-up resistor).
While nSTRT is LOW during the power-up sequence, the MCP16502 expects the assertion of the PWRHLD signal (power-hold) from the MPU to continue the sequence.
PWRHLD may be already HIGH in a typical application using a backup supply. If PWRHLD has NOT been asserted HIGH by the MPU before completion of the start-up sequence (i.e., when nRSTO is asserted high), the MCP16502 automatically initiates a turn-off sequence.
After the assertion of PWRHLD, nSTRT should be released before the long-press time-out timer expires.
During run time (PWRHLD=HIGH), the nSTRT (thus nSTRTO) can be asserted LOW again. No automatic action is taken by the MCP16502 in this case unless the push button interrupt assertion time-out delay expires without any action from the MPU.