In the BQ25619/618, the accessory devices can be connected to the charger PMID pin to get power either from the adapter through the Q1 direct path or from battery Boost mode. An optional external PMOS FET can be placed between the charger PMID pin and accessory input to disconnect the power path during overcurrent and overvoltage conditions. PMID_GOOD is used to drive an external PMOS FET through an inverter. PMID_GOOD HIGH turns on an inverter to pull the PMOS FET gate low to turn on the PMOS FET, and PMID_GOOD LOW turns off the PMOS FET.

Upon adapter plug-in, PMID_GOOD goes from LOW to HIGH when VBUS rises above the battery but below V_ACOV, and passes poor source detection. During the operation, PMID_GOOD goes from HIGH to LOW if Q1 current exceeds 115% of the IINDPM threshold, (I_{BLK_OCP}), or adapter voltage rises above 5.8 V (V_{BST_OVP}).

The high-voltage adapter over V_{BST_OVP} keeps charging the battery if all conditions are valid. The external PMOS FET stays off to protect the accessory from an overvoltage fault.

When the adapter is removed, PMID_GOOD goes LOW before battery Boost mode starts.

In battery Boost mode, the device regulates PMID voltage between 4.6 V to 5.15 V as a stable power supply to the accessory devices. PMID_GOOD goes from LOW to HIGH when PMID voltage rises above 3.8 V (V_POORSRC). Similar to the adapter present scenario, the PMID valid voltage range is between V_POORSRC and V_{BST_OVP}. Once PMID voltage is out of this range, PMID_GOOD goes LOW to disconnect the accessory device from PMID. During Boost mode, all of the conditions to exit Boost mode will drive PMID_GOOD from HIGH to LOW, including Boost mode disable in register, ACOV, TS fault, battery depleted (V_{BAT_DPL}), BATFET overcurrent, (I_{SYS_OCP_Q4}), etc.