MCU Supply Ramp Rate S32K116

[donald3]

My application is simple automoive body electronics module and I am considering the S32K116.

AN5426 says that MCU supply must ramp monitonicly and if it does not the device may be stuck or damaged.  The min and max rampt rates are so wide they are not an issue.

Normally, non monotonic supply can happen for example when turned off and back on or there is bounce in the on/off switch (like in ignition switch in this case).  Traditionally we use Brown out reset or LVR to recover this condition but it seems for this part, that is not sufficient.

If the device is just fed from a LDO regulator in Automotive application the supply could easilly be non monotonic due to switch bounce on the supply feed etc.  What does NXP recomment for power management in very small systems using this processor for Automotive applications?

[PavelL]

Hello @donald3 ,

For the S32K1xx devices, the requirement for a monotonic power‑supply ramp in AN5426 refers specifically to the initial power‑up ramp through the operating thresholds of the internal POR/LVD circuits. This requirement is common to most ARM‑based automotive MCUs and is intended to avoid undefined digital states during startup.

A short non‑monotonic event on the battery or ignition line does not damage the device by itself. The risk occurs only if the supply oscillates exactly in the region where the internal analog reset circuitry is transitioning, and the MCU may fail to exit reset cleanly. This is why AN5426 recommends a monotonic ramp during power‑up.

Once the device has passed POR and is running, the LVD/BOR modules will correctly trigger a reset when supply dips below their thresholds.

Please check the S32K116_0N96V errata, item ERR052092. It recommends using an external regulator capable of supplying the specified voltage with a minimum current of 200 mA.

Best regards,

Pavel

[donald3]

Thanks for the prompt reply.  Thanks for the reference to the Errata item as well.

I understand the applicability to the initial power-up but what criteria to use to decide if this is an initial power up.  How low can the supply voltage go before the supply voltage must get close to 0 and rise monotonicly again.  Also how close to 0v is required for the next 'initial power-up'?

[PavelL · Accepted solution]

Hello @donald3 ,

I apologize for delayed response caused by vacations.

As far as I know, there's no such a requirement.

Best regards,

Pavel