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TPS659037: How to remove the depency of switch for PWRON pin with permanent software changes?

Nanjunda M
Expert 2485 points
Part Number: TPS659037

Hi,

I'm using the PHYTEC's phyCORE-AM57x SOM, which uses the TPS6590374 as PMIC for the AM572x SOC.

The TPS6590374 has the connection of the x_PWRON pin connected to the switch and GPIO_7 connected to ground permanently making it powerON always from the switch.

I would like to remove the dependency of the switch for PWRON pin. So is it possible to do this with any register settings ?

Below is the part of circuit for reference:

Thanks & Regards,

Nanjunda

  • 0
    TI__Genius 12735 points

    Hi Nanjunda,

    Are you able to depopulate R66 and populate R68 on this board? You will not be able to change any register settings until the TPS6509374 part is powered up.

    I will also loop in the expert for this part to see if they have any further suggestions for this use case.

    Best regards,

    Layne J

  • 0
    TI__Genius 10000 points

    Hi,

    There are two options for powering up the device (see ON Requests table in the datasheet). The first option is PWRON. This requires a push button followed by either a write to DEV_ON bit or pulling POWERHOLD high to keep the device on.

    The second option to turn the device on is to just use POWERHOLD (GPIO_7). In this case, no push button is needed and PWRON is left floating. POWERHOLD works like an enable signal. When it is pulled high, the device turns on. When pulled low, the device turns off.

    Also, TPS6590374 is not recommended for new designs. I recommend moving to the pin compatible TPS6590378 for new projects. The differences between these two devices are explained in our user guide: http://www.ti.com/lit/pdf/sliu011

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Nastasha said:

    The second option to turn the device on is to just use POWERHOLD (GPIO_7). In this case, no push button is needed and PWRON is left floating. POWERHOLD works like an enable signal. When it is pulled high, the device turns on. When pulled low, the device turns off.

    Hi Natasha/Layne,

    Thanks for the response. I too have read about this options in your other post replies. But is it right to keep the GPIO_7(POWERHOLD) always high, by mounting the R68 and removing R66 as suggested by Layne in my circuit? Will this permanently solve my problem?

    Do I need to do anything else along with above process?

    This is a old design and we are going with the production release for IC TPS6590374. So will be using this at this point of time.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    If POWERHOLD is always high, then it cannot be used to disable the device If you remove power while POWERHOLD is still high, all the rails will shut off at the same time, which is not a recommended solution for the processor. To address this issue, I recommend making sure that there is a valid "OFF Request" present.

    The datasheet has a table of "OFF requests" that can help provide options for turning off the device.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Nastasha said:
    If POWERHOLD is always high, then it cannot be used to disable the devic

    Hi Natasha,

    I think I'll be ok with this case. So in this case the power ON and OFF happens without any intervention right? except the fact that the power off sequence wont be followed. 

    Could you please let me know what are the effects of this if I go ahead with system of not following power off sequence for the processor would effect on a long run.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    You are correct, the power down solution will not be followed if you remove power to disable the device.

    Please check the datasheet (under "Application and Layout" section, in VCCA section). There is a possibility to damage the PMIC by turning of the device in this manner. other pins like RESET_IN for example can be used as an OFF request to disable the PMIC before removing power.

    For the processor, you may want to post a question on the processor forum to see if there are any concerns about powering the device off without following the recommended power down solution.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Hi Natasha,

    We found a intermediate solution to replace the switch with a reset supervisory output. I hope that wouldn't create any issue for the whole power sequencing issue (Power ON or power down).

    Please let me know if that's not correct.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    Please explain how the reset supervisor is used if you would like any feedback on any power up or power down concerns. I do not have enough information to give you a clear yes/no feedback without knowing what signal is being supervised and what signal is being reset.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Hi Natasha,

    We have connected the active low supervisory IC output to PWRON pin and we have given the power input to one of the external powers (3.3V) on our board.

    We have set a delay of 5s through the capacitor option present on the supervisory. So ultimately we will get a low pulse for 5s and then the output of supervisory goes high. We have used TPS3808G33DBVR for this. The sense and VCC are connected to the same power signal.

    Please let us know if any issue with this setup.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    The long press signal on PWRON has a default of 12 seconds required for the pin to be low before the device will turn off. The shortest option (if set through I2C) is 6 seconds. I think you will need to adjust the supervisor reset signal if you want to use this to turn off the device.

    The other option is that if the supervisor stays lows when the voltage monitored is too low, than the reset signal could be connected to a pin such as RESET_IN to put the PMIC in standby when the input voltage is not sufficient. This would not need any delay to turn off the PMIC (where as the PWRON method requires 6-12 seconds).

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Hi Natasha,

    The purpose of the supervisory used is just to auto power ON, as the power OFF control will be taken care by the software commands.

    Is giving a 5seconds is too much ? What is the minimum duration of low needed for the power ON ? Could you please specify.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    Your supervisor could just be connected to POWERHOLD (GPIO7) and then it would turn on the PMIC when the output of the supervisor went high, and turn off the PMIC if the output goes low from loss of power. Then, you wouldn't need to use PWRON and have these long delays.

    Thanks,

    Nastasha

  • 0 in reply to Nastasha
    Expert 2485 points

    Natasha,

    Well, that option is not available for me, as I'm using the PHYtech-AM57xx SOM board in which the TPS659037 is mounted. And only the PWRON pin is available for the control out of the SOM board..

    So could you please comment on the delays part of my last post.

    Thanks & Regards,

    Nanjunda M

  • 0 in reply to Nanjunda M
    TI__Genius 10000 points

    Nanjunda,

    If you are using PWRON, you need a push button signal (high-low-high) to turn the device on, followed by POWERHOLD or DEV_ON going high within 8 seconds.

    To turn the device off, you need a long-press-key (where the PWRON pin is held low) for at least 12ms if using the default settings.

    If you want, you can configure the long press time to be 6ms by changing the settings in the LONG_PRESS_KEY register through I2C after startup.

    Thanks,

    Nastasha