Cannot reset MCU when pulldown POR = 0

[thanhnambka]

Hi all,

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

I am test following 4 step:

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

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

[thanhnambka]

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?

[diego_charles]

Hi @thanhnambka 

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. 

[diego_charles · Accepted solution]

Hi @thanhnambka 

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