The MCU LDO has an undervoltage monitor to notify the MCU if the LDO falls out of regulation. This monitor is enabled any time the MCU LDO is enabled and its status is in the MCU_PG register bit. A 125-μs deglitch time rejects load and line transient spikes that may briefly drop the MCU LDO voltage below the under-voltage threshold. If MCU_PG is low while the MCU LDO is enabled and it has been more than 10 ms since the LDO was enabled or changed voltage, the MCU_ERR register bit latches high. When the MCU_ERR bit is set high and the MCUERR_DIS bit is low, the MCU LDO fault state is entered.

Two scenarios can cause the LDO to drop voltage:

• input voltage (PLDO) drops
• load current exceeds the LDO current limit

If the input voltage drops, it can be because the boost converter is disabled. If the load current exceeds the LDO current limit, the die temperature could exceed safe limits. The MCU fault state automatically enables the boost converter and temperature monitor (OTS_EN) to handle both of these cases. The device disables all analog blocks to prevent further issues caused by an underpowered MCU.

There are two methods to exit the fault state. Every second in the fault state, the MCU_PG register bit is automatically read. If high, the fault state is exited. The MCU_ERR bit remains high until the STATUS1 register is read. Alternatively, if the STATUS1 register is read and MCU_PG is high, the fault state is exited. When the device exits the MCU_ERR fault state, the device re-enables all blocks that were enabled before the fault state occurred.

If an over-temperature fault occurs while in the MCU LDO fault state, the device enters the over-temperature fault state. The over-temperature fault state disables the MCU LDO and boost converter in addition to the blocks that are disabled by the MCU LDO fault state. After the device exits the over-temperature fault state, it immediately re-enters the MCU LDO fault state to confirm the MCU LDO status.