POF — Power-fail comparator

The power-fail comparator (POF) provides the host with an early warning of an impending power supply failure.

POF is generated from an always active comparator monitoring the voltage on the VSYS pin. It can be configured through POFCONFIG to give a warning through a GPIO to the host.

If voltage on the VSYS pin drops below VSYS_COMP, but voltage remains above the respective BOR threshold on the VBAT or VBUS pins, the VSYS pin is disabled after t_POFWAIT and registers are reset after t_PWRDN. If VSYS > VSYS_COMP, the chip powers up after t_PWRDN. See Power fail warning.

A warning is issued in the following cases:

• VBUS is removed while the battery is empty or not connected (VBAT < VSYS_POF)
• VBUS rises above VBUS_OVP while the battery is empty or not connected (VBAT < VSYS_POF)
• The battery is removed when VBUS is not connected
• The battery discharges until VBAT < VSYS_POF and VBUS is not connected
• Battery voltage drops momentarily below VSYS_POF and VBUS is not connected

Figure 1. Power fail warning

Figure 2. Power removal

To use the POF warning feature, set POFWARNPOLARITY and POFENA to 1 in register POFCONFIG. GPIO settings are located in GPIO — General purpose input/output.