5.16 Limp Home

The Limp Home function is a high-voltage output pin used for signaling unexpected system errors. The LH pin is driven by an open-drain NMOS switch and is activated by the following events:

• A watchdog failure or Reset event. A watchdog timeout event in Sleep mode will not activate LH.

• If the device is in Standby or Normal mode:

  V_VDD1 < V_{VDD1_UV_Set} and RSTLVL bit = ‘1’ (ATA6847-5050) or

  V_VDD1 < V_{VDD1_UV_IO_Set} (ATA6847-5050/ATA6847-3333) or

  V_VDD2 < V_{VDD2_UV_IO_Set} (ATA6847-5033)

• V_VDD1 < V_{VDD1_UV_Set} and RSTLVL bit = ‘1’ (ATA6847-5050(L)) or

  V_VDD1 < V_{VDD1_UV_IO_Set} (ATA6847-5050 / ATA6847-3333(L)) or

  V_VDD2 < V_{VDD2_UV_IO_Set} (ATA6847-5033(L)) has been detected for longer than t_Reset after entering MCU Reset mode, triggered by a wake-up or interrupt event (see cases e AND i in Device Operating Modes).

• VDDIO overvoltage event has been detected .

Releasing the LH pin to high ohmic, after the ATA6847/ATA6847L transitions from MCU Reset mode into Standby mode, requires receiving three valid watchdog trigger values (0x55) via SPI.