i.MXRT1064 PMIC_ON_REQ Output Not Deactivated on Power-Off

[Vagni]

I developed my custom board based on the i.MXRT1064 cpu and referring to the MIMXRT1064EVK board. I used the same power supply hardware architecture of the MIMXRT1064EVK board: my board power-up is correct, the cpu start properly, the same for power-off. An ONOFF pushbutton is not used, so the mcu ONOFF input pin is unconnected.

On my board the VDD_SNVS_IN is supplied by a CR1220 coin battery for the internal RTC functionality and also for an external NVRAM memory device.

My issue: if my board is kept in power off for more than 30 days, the coin battery results completely discharged, with or without the NVRAM device.

PMIC_ON_REQ output belongs to the VDD_SNVS_IN domain: I see it is never deactivated when the main supply switches off, so the battery is drained through the internal 100K PMIC_ON_REQ pullup and the external 10K resistor.

PMIC_ON_REQ current path in OFF state

How can I get PMIC_ON_REQ low when my board is switched off?

Is it possible through software?

Or should I use an ONOFF pushbutton? But how?

[jingpan]

Hi @Vagni ,

RT1064 can go into SNVS mode by software, ONOFF button is not a must. PMIC_ON_REQ can deactive when go into SNVS mode by software.

Please check the power_mode_switch demo in SDK.

Regards,

Jing

[Vagni]

Thank you @jingpan .

The power_mode_switch demo in SDK let RT1064 enter in SNVS low power mode and exit out of reset through the WAKEUP pin. Unfortunately, on my board the WAKEUP pin is floating (unconnected).

I need to wakeup RT1064 from SNVS mode when power supply is reconnected to my board: how can I achieve this?

[jingpan]

Hi @Vagni ,

My question is how can RT1064 know it's main power come back? Here is all the wake up source.

Besides that only ONOFF can power on the chip. /POR can't.

Regards,

Jing

[Vagni]

Hi Jing,

On my board I have a power-fail analog signal (a resistive voltage divider on the main supply voltage) used as interrupt source with the internal comparator (CMP4_IN6) to know when the main power is switched off.

I see RTC can be a wakeup source from SVNS low power mode, but till the main power come back the mcu cannot exit out of reset and check the power-fail input signal at every RTC wakeup interrupt, right? The mcu can wake up only if \RESET is not active, right?

If I use RTC as wakeup source from SVNS mode, at the first RTC interrupt does PMIC_ON_REQ return high even if \RESET is low?

[jingpan]

Hi @Vagni ,

Coin battery also connect on VDD_SNVS_IN. PMIC_ON_REQ and WAKEUP pin are in SNVS domain. RTC is SNVS domain too. I think the PMIC_ON_REQ will assert by RTC even VDD_HIGH_IN is not power up.

I think it's better to use WAKEUP pin.

Regards,

Jing