SNVS_PMIC_ON (AB8) seemingly being driven high when RTC battery is attached.

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SNVS_PMIC_ON (AB8) seemingly being driven high when RTC battery is attached.

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eedev
Contributor I

I am working on a board using the i.MX7D and PF3000 PMIC. The SNVS_PMIC_ON signal from the i.MX is driving the PMIC's PWRON pad. When powered off this should be LOW. And that is true if I run the poweroff command from linux, or by setting the "TOP" bit of the SNVS_LP register.

However when the RTC battery (powers VDD_SNVS_IN) is first inserted  or when power is removed abruptly (power cord is pulled out), the SNVS_PMIC_ON signal from the i.MX is HIGH (about 2.5v) which is apparently enough to turn on the PMIC enough to draw too much current from the battery. It's not a lot, but it matters for this application.

How can I get the SNVS_PMIC_ON to go and stay low when power is removed from the board? Is there a SNVS register I'm missing or something?

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Evan

seems this behaviour complies with description in Table 6-8.

Power mode transitions i.MX7D Reference Manual
"ON, first time - Either coin cell or SoC power supply is connected to SNVS."
http://cache.nxp.com/files/32bit/doc/ref_manual/IMX7DRM.pdf

I am not aware of special SNVS register settings for case when power is

removed from the board, but when power is removed abruptly there may be

corruption of nand or emmc images, if there is current data transfer from them.

Best regards
igor
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eedev
Contributor I

Thank you, that makes sense for the first time. We are using a write only partition for the linux image, with special partitions for writable things like logs.

What is the expected state when power is removed abruptly? Is it undefined, or just remains in the ON state? In other words I'm trying to determine if it is normal for abrupt power removal to leave the SNVS_PMIC_ON signal from the i.MX, or if I'm doing something wrong in software.

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