RT1170: Using ONOFF pin with external PMIC

[marcoosi1]

Referring to i.MX RT1170 Processor Reference Manual, Rev. 2, 06/2023:

I intend using the RT1170 with an external PMIC. Figure 25-3 and the following table describe the ONOFF input of the MCU not to be connected and instead use a button input on the PMIC.

Is there any reason for not using the ONOFF input of the MCU with an external PMIC to control the PMIC_ON_REQ line?

From my understanding, e.g. when doing the `Emergency On to OFF, by button` action (long press ONOFF), the PMIC_ON_REQ should go low even when using an external PMIC.

[Pavel_Hernandez]

Hello, my name is Pavel, and I will be supporting your case, I believe this could be by the power sequence of the MCU. I recommend reviewing the HDG I will attach to the thread.

4.2.1.2 Power-down sequence
The following restrictions must be followed:
• VDD_SNVS_IN supply must be turned off after any other power supply or be connected (shorted) with VDD_LPSR_IN and DCDC_IN supply.
• If a coin cell is used to power VDD_SNVS_IN, then ensure that it is removed after any other supply is switched off.

Best regards,
Pavel

[marcoosi1]

Hi Pavel, thank you very much for your answer. I have consulted the HDG and am fully aware of the power sequencing. The VDD_SNVS_IN line is indeed powered by a dedicated LDO or battery to ensure the correct sequence.

What I was not sure is why the Reference Manual refers to using the push-button input of the external PMIC rather than the MCU's ONOFF pin. But from your answer, I understand that as long as VDD_SNVS_IN is individually powered before the PMIC starts, it would be ok to use the ONOFF input to control the PMIC_REQ_ON line?

[Pavel_Hernandez]

Hello, sorry for the late response I was asking for more details about your questions.

The user could use the logic of the external PMIC to power on the MCU or the ON/OFF pin from the MCU, the ON/OFF pin trough to the state machine and then send the signal trough PMIC_REQ_ON to the external PMIC to request a power-on.
The PMIC is responsible to turn on the rest of the MCU, the user could use the schematic on the RM or use the pin. The user could decide whether to use the external PMIC logic or the extra step using the pin.

Best regards,
Pavel

[Pavel_Hernandez]

Hello, my name is Pavel, and I will be supporting our case, let me get into your case, when I have more information, I will contact you.

Best regards,
Pavel