i.MXRT1064 PMIC_ON_REQ High Voltage Level

[Vagni]

I developed my custom board based on the i.MXRT1064 cpu and referring to the MIMXRT1064EVK board.

My board power-up is correct, the cpu start properly. But I noticed PMIC_ON_REQ active high is about 1.6V, while VDD_SNVS_IN is 3.3V: is it correct? I expected a 3.3V high level on PMIC_ON_REQ; PMIC_ON_REQ belongs to the VDD_SNVS_IN domain, right?

As on the MIMXRT1064EVK, PMIC_ON_REQ drives the enable input of my external DCDC through an RC network (10K - 220nF) and the DCDC enable input pull-down resistance is about 100K, so the DCDC enable input current is very low.

On the MIMXRT1064EVK, after the cpu is out of reset and started, I measure about 2.8V on PMIC_ON_REQ. Why?

I ask this because I need to use PMIC_ON_REQ output to also enable other external power supplies on my board system and I need to be sure about its high and low voltage levels.

Thanks!

[Vagni]

Looking the i.MX RT1064 Reference Manual I see the IOMUXC_SNVS_SW_PAD_CTL_PAD_PMIC_ON_REQ register:

From its reset value it seems on PMIC_ON_REQ output both 100 KOhm  pullup and Open Drain function are enabled. So the PMIC_ON_REQ high voltage level is generated by its internal pullup.

Could this be the cause of my 1.6V measure with an external 100 KOhm pulldown resistor?

The PMIC_ON_REQ is not a CMOS output at power-up.

[Pavel_Hernandez]

Hello,
Yes, the PMIC_ON_REQ belongs to the domain of VDD_SNVS_IN, and the maximum voltage is provided by this. The operating range of VDD_SNVS_IN is 2.4v minimum and 3.6v maximum. If you want to use an external PMIC instead of DCDC, you still need to power DCDC_IN. DCDC_PSWITCH must be connected to the ground to disable DC/DC, and DCDC_LP must be left floating. These recommendations are found in the Hardware Design Guide I suggest following the recommendations.