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AM335x with TPS65910AA1SRL hang

Andrea Sorio
Intellectual 265 points
Other Parts Discussed in Thread: AM3359, TPS65910

Dear Sirs

I developed a custom board with an AM3359 processor and a TPS65910AA1 PMIC.

I would like to use the PMIC RTC.

I connected a SuperCAP to PMIC.

When I switch on the system with Supercap discharged, the system  boots.

When I switch on the system with Supercap charged the system doesn't boot.

If I remove the usdcard , the processor doesn't print the 'C" letter to the uart.

Could you be so kind as to suggest me what do I have to check?

Thank you in advance

Best Regards

Andrea Sorio

  • 0
    TI__Guru**** 393215 points
    Hi Andrea,
     
    It would help very much if you can post the PMIC - AM335X part of your schematic.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru**** 393215 points

    Just got the schematic from Alberto. I will look through it and reply here.

  • 0 in reply to Biser Gatchev-XID
    TI__Guru**** 393215 points
    Hi Andrea,
     
    Here are some comments. Unfortunately the PDF you sent is not text-searchable, and unmounted components are not marked, so I wasn't able to trace everything. However:
     
    1. If U8 is mounted this is probably what causes the problem. This part should be removed.
    2. R110 should be removed.
    3. Ether R67 or R109 should be removed.
    4. The AM335X EXT_WAKEUP pin seems to be floating. If it isn't connected anywhere it should be tied to GND.
    5. R7 should be removed.
    6. An external 4.7kOhm pullup should be added to GPMC_WAIT0.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    Hi Biser

    Thank you for your replay.

    On my board the mounted components are:

    R110

    IC9 (I would like to remove it to manage the reset with IC8)

    R109 (for switching feedback)

    The not mounted components are:

    IC10 (I wouldn't like to use an external power for VRTC)

    IC8

    R67.

    With this configuration and with TP65910 VBACKUP pin floating, the system works fine.

    With a discharged super cap the system boots fine, as soon as the super cap voltage goes above

    1.8-.19 V the system doesn't boot

    The system starts as soon as I feed the 5V to it.

    When, from linux console, I execute the "shutdown -h now" command , the system switch off correctly.

    With EXT_WAKEUP tied to ground and GPMC_WAIT pulled to ground, nothing is changed.

    Any idea?

    Thank you in advance

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points

    Andrea Sorio said:

    With a discharged super cap the system boots fine, as soon as the super cap voltage goes above 1.8-1.9 V the system doesn't boot.

    The system starts as soon as I feed the 5V to it.

    I don't understand - do you expect the system to boot from the supercap?

  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    No, of course

    The super cap has to maintain the RTC running while 5V isn't preset.

  • 0 in reply to Andrea Sorio
    Intellectual 265 points

    the strange thing is that TPS65910 VBACKUP is a power pin

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points
    Andrea,
     
    Can you tell me the voltage on the PWRHOLD signal when the board won't start (supercap charged, 5V not present)?
  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    Hi Biser


    When the board starts correctly  PWRHOLD is at 1.8V

    When the board doesn't start (super cap charged) PWRHOLD is at 0.0V


    Thank you

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points

    Is this before or after you try to start the board? Can you tell me the expected startup behaviour - by applying +5V or by pushbutton?

  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    Hi Biser

    My board stars as soon as I apply +5V.
     I don't use push button .

    with system off and super cap not charged , PWRHOLD is low and  PMIC_VRTC is 0V.

    When super cap isn't charged the system boots.

    Now I apply  +5v, system boots.

    If, from linux console, I switch off the system  with "shutdown -h now", whit super cap not charged, and without +5V applied, PWRHOLD is low, and PMIC_VRTC is at 0V.

    If now I apply +5V the system restarts.

    With system running u-boot console, I enable the super cap charging, writing 0x5 to BBCH_REG.

    I wait for a full super cap charge without running linux.

    As soon as the super cap is charged, I remove +5V. and PWRHOLD is hight (1.8V) and PMIC_VRTC is at 1.8V.

    If now I apply +5V the system boots.

    Now, from linux console, I switch off the system with "shutdown -h now".

    When the system is down, I remove the power (+5v).

    Now PWRHOLD is low and PMIC_VRTC is at 1.8V.

    If now I apply +5V again the system doesn't boot!

    I did another test: with PWRHOLD low and PMIC_VRTC at 1.8V, applying +5V the sytem doesn't start, but if i force the PWRON low, the system starts for 3/4 second and then stops, but PWRHOLD remain low.

    Tell me if I have to do other tests.

    Thank you

    Bye

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points
    Hi Andrea,
     
    Can you give me some more information please? Do you intend to use system low-power modes (suspend, standby)? Or you just need the PMIC RTC for timekeeping when system is off?
  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    Hi Biser


    I need VRTC only for time keeping.

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points
    OK. In this case I will suggest you make the following changes:
    1. Disconnect PWRHOLD from AM335X and tie it to VDD_5V. Keep in mind that this PMIC input is tolerant up to +5.5V. If VDD_5V goes higher than that place a resistive divider.
    2. Remove R110, place IC10, C140, C142 and C144.
    3. Remove IC7 and IC8, place X2, C37, C38 (and R43 if necessary), remove R47.
    4. If possible tie EXT_WAKEUP to ground.

    This should make it work.

     

  • 0 in reply to Biser Gatchev-XID
    Intellectual 265 points

    Hi Biser

    With this configuration it should be possible to control the state of processor with PMIC_POWER_EN: high: processor running, low processor switched off.

    Furthermore it should be possible switch on and off the processor with push button (PWRON signal).

    When the system starts it should read the correct time from TPS65910 and setup the processor RTC.

    Isn't it?


    Thank  you


    Bye

    Andrea

  • 0 in reply to Andrea Sorio
    TI__Guru**** 393215 points
    Hi Andrea,
     
    PMIC_POWER_EN is an output signal from the processor. The PWRON signal should still be functional, but the system will start directly when power is first applied. Setting up the processor RTC should be no problem once the system is running.