topic Re: Cannot reset MCU when pulldown POR = 0 in i.MX RT Crossover MCUs

Cannot reset MCU when pulldown POR = 0

namht — Thu, 02 Feb 2023 03:45:31 GMT

Hi all,

I'm using MCU MIMXRT1051CVL5B. In power of SOC, i design following IMXRT1050-EVKB schematic.

I am test following 4 step:

MCU_DCDC_IN = 3.3V → DCDC_OUT = 1.2V.
Drop MCU_DCDC_IN = 2.8V → DCDC_OUT = 0.0V.
Restore MCU_DCDC_IN = 3.3V → DCDC_OUT = 0.0V.
I am pulldown POR = 0, however DCDC_OUT = 0.0V.

My question: How to reset MCU in my test case?

Re: Cannot reset MCU when pulldown POR = 0

diego_charles — Tue, 14 Feb 2023 19:08:47 GMT

Hi @namht

I hope you are doing well!

When dropping MCU_DCDC_IN = 2.8V I presume that VDD_SOC_IN = 0.0v.

MCU_DCDC_IN = 2.8V → DCDC_OUT = 0.0V.→VDD_SOC_IN = 0.0v.

As your schematic shows that VDD_SOC_IN is connected to DCDC_OUT.

Being that correct, the only proper way, I can think of, to recover the MCU is to do a power cycle. Let me explain below.

There is one scenario when VDD_SOC_IN can be 0.0v is, this when the MCU enters in SNVS low power mode. The MCU is able to enter into SNVS mode via SW or HW (this is pulling down the ONOFF pin) In SNVS mode external PMIC and several power rails are shutdown, this includes the VDD_SOC_IN.

When the MCU recovers from SNVS ( by externally pulling up the ONOFF pin or via peripheral wake up) there is a power cycle sequence almost similar to the typical power-up sequence.

Please note that you processor have not entered into SNVS mode. It is very likely that it was shutdown improperly, thus a power cycle should fix your issue. SNVS does almost the same to a the power cycle to recover the MCU when VDD_SOC_IN was previously at 0.0v.

Best regards,

Diego

Re: Cannot reset MCU when pulldown POR = 0

namht — Thu, 09 Feb 2023 10:15:07 GMT

Hi @diego_charles . Thanks for your reply.

According to you, in step 4, MCU enter to SNVS Mode. To put MCU back into Run Mode, i need reset MCU_DCDC_IN (power down 0V then power on 3.3V), right?

Re: Cannot reset MCU when pulldown POR = 0

diego_charles — Tue, 14 Feb 2023 19:10:34 GMT

Hi @namht

I edited my previous reply with more details.

Basically I suggest you to do a power cycle to recover the MCU.

Let me know if you encounter more issues.

Thank you.