Power supply supervisors

The power supply supervisors monitor the connected power supply and provide the following functionality.

  • Power-on reset (POR) — signals the circuit when a supply is connected
  • Fixed brownout reset detector (BOR) — holds the system in reset when the voltage is too low for safe operation
  • Optional power-fail comparator (POF) — signals the application when the supply voltage drops below a configured threshold

The power supply supervisors are illustrated in the following figure.

Figure 2. Power supply supervisors
power supply supervisor

Power-fail comparator

Using the power-fail comparator (POF) is optional. When enabled, it notifies the CPU of a potential power supply failure.

The POF can measure the voltage on VDD . To enable and configure the POF, see register POFCON.

When the supply voltage falls below the defined threshold, the POF generates an event POFWARN that can be used by an application to prepare for power failure. This event is also generated when the supply voltage is already below the threshold at the time the POF is enabled, or if the threshold is reconfigured to a level above the supply voltage. POFWARN is disabled using the EVENTDISABLE field of REGULATORS.POFCON. In addition to the event, the result of the POF is found using POFSTAT.

POFWARN prevents RRAMC from performing write operations to the non-volatile memory. See RRAMC — Resistive random access memory controller for more information about non-volatile memory.

The POF features a hysteresis of VHYST, as illustrated in the following figure.

Figure 3. Power-fail comparator
The power-fail comparator has built in hysteresis that prevents oscillations if the voltage is close to the threshold

To save power, the POF is not active in System ON when the HFCLK is not running, or in System OFF.

To measure the voltage, perform the following steps.
  1. Disable POFWARN by writing Disabled to REGULATORS.POFCON.EVENTDISABLE.
  2. Enable POF by writing Enabled to REGULATORS.POFCON.POF.
  3. Loop over all threshold voltages by writing a threshold voltage into register REGULATORS.POFCON.THRESHOLD, starting at the lowest value enumerator until REGULATORS.POFSTAT toggles. This toggle indicates that the voltage has been found and can be read from register REGULATORS.POFCON.THRESHOLD.