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Linux: CR-2032 back up battery is draining too fast, even though PMIC goes to RTC only mode.

Sanju Bisanal
Prodigy 40 points
Other Parts Discussed in Thread: TPS65910, AM3352

Tool/software: Linux

We have a custom board based on am3352, powered by tps65910 PMIC which gets power from an external adapter (24v,5A), PMIC is going to RTC only mode on giving "poweroff" command, but want to know whether it goes to RTC only mode on power cut, below is the snapshot of the power supply from PMIC, linux kernel version 3.14. 

  • 0
    TI__Guru**** 393215 points
    Hi,

    It's the AM335x that goes to RTC-only mode, not the PMIC. When the input power supply to the PMIC is off the entire system will have no power supply.
  • 0 in reply to Biser Gatchev-XID
    Prodigy 40 points
    Hi Biser,
    Thank you for your quick reply, yes its AM335x which goes to RTC only mode by making "PMIC_PWR_En" pin off PMIC low on giving "poweroff" command, but when the power goes off, i probed "PMIC_PWR_En" pin it was still high, so my doubt is whether it dissipates more power during this time, since the battery is draining fast. And is there any means to make it low during power cut.
  • 0
    TI__Genius 13567 points
    Hi Sanju,

    "RTC-only mode" describes the state when all supplies are turned off except for VDDS_RTC and CAP_VDD_RTC on the AM335x. During debug, please check your supplies to verify if RTC-only mode is entered.

    When an RTC alarm is set, it will drive the "PMIC_PWR_EN" pin to turn on the PMIC after some time. The PMIC_PWR_EN pin by default always stays high unless you configure the output in the RTC registers (section 20.3.3.8 of the AM335x TRM). You need to set these registers to keep PMIC_PWR_EN low until the alarm expires.

    Regards,
    Ahmad
  • 0 in reply to Ahmad_Rashed
    TI__Genius 13567 points
    Hi Sanju,

    Let me add... the PMIC_PWR_EN pin should go low after you perform a shutdown using the "poweroff" command. This is built in to the "rtc-omap.c" driver where it uses the ALARM2 interrupt to set PMIC_PWR_EN low after using the "poweroff" command. If the PMIC_PWR_EN pin stays high then there is some configuration that is not matching the SDK / driver default configuration.

    To resume from RTC-only mode, you will configure the RTC to wake from either an ALARM event or from the EXT_WAKEUP pin.
  • 0 in reply to Ahmad_Rashed
    Prodigy 40 points
    Hi Ahmad,

    Thank you for your valuable inputs, on giving "poweroff" command AM335x goes to RTC only mode everything works as expected, but the only problem is we are using an adapter (24v,5A) to power up our board, on turning it off without running "poweroff" command the " PMIC_PWR_EN" pin still stays high, is there any ways to make it low.
  • 0 in reply to Sanju Bisanal
    TI__Genius 13567 points
    Why does your chip go to RTC-only mode when you give it the poweroff command? It should power off unless you modified the RTC registers.