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AM3354ZCZ72 processor power up with PMIC TPS65217C

Rajput Ajay
Intellectual 310 points
Other Parts Discussed in Thread: TPS65910A

Hi,

I am having problem in my design including processor AM3354ZCZ72 power up through PMIC TPS65217C. At intial startup of board, PMIC start output on LDO1 i.e. 1.8V which is connected to VDDS_RTC pin of processor. As 1.8V is started, the processor provides PMIC_enable signal to PMIC after which PMIC generates other supplies necessary for the processor. As soon as processor starts, the hyperteminal receives data "C" on PC.

Problem is that as processor starts up,  the voltage of LDO1 becomes 2.4V  from 1.8V as soon as processor starts. So, i am not able to understand that why LDO1 output of PMIC changes from 1.8V to 2.4V as soon as processor starts.

We also checked that the Processor dosen't configures anything to LDO1 output register of PMIC through I2C. When we read the PMIC register settings regarding LDO1, it shows the setting of 1.8V only.

I had compared my design with the TI starter kit and i am not finding any difference which can create such problem.

Regards,

Ajay

  • 0
    Guru 31670 points

    Ajay,

    Did you check the section "WAKE-UP AND POWER UP SEQUENCING"  in the datasheet? 

    http://www.ti.com/lit/ds/symlink/tps65217c.pdf

  • 0 in reply to Renjith Thomas
    Intellectual 310 points

    Hi,

     

    Please can you explain in details that what should i check in the section of "Wake Up and Power up sequence" of TPS65217C PMIC datasheet. We have found that in our schematic, we have connected LDO1_1.8V to VDDS_RTC pin of AM3354ZCZ72 processor. If we remove this connection, LDO1_1.8V remains at 1.8V for 5s and then PMIC shut down due to no PMIC_PWR_EN signal from processor. But, when we connect the LDO1_1.8V to VDDS_RTC pin, PMIC and processor starts but 1.8v of LDO1 becomes 2.4V.

     

    Regards,

    Ajay

  • 0 in reply to Rajput Ajay
    TI__Guru**** 393215 points
    Hi Ajay,
     
    Please check if you have any pull-up resistors to 3.3V, on the 1.8V signal lines. This may cause parasitic leakage. From what you describe looks very likely.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 310 points

    Hi Biser,

    I have checked my schematic and i found that there was a pull up from 3.3V to USB1_ID pin which should be at 1.8v. Apart from these, we are not using any 1.8V signal lines as all VDDSHV1-6 are connected with 3.3V supply and no digital peripheral on board is working at 1.8V IO supply.

    I removed that particular pull-up resistor but still i was getting 2.4v insteed of 1.8v on LDO1 of PMIC which is connected to VDDS_RTC of processor.

    Then, we connected a load of 330E on VDDS_RTC pin and then we were able to get 1.8V to 1.9V on the LDO1 pin.

    so, is load required on that pin to keep it at 1.8v. When i check beaglebone schematic, i found that they had used a AND gate which is powered by VDD_RTC. OR Can there be anything related to power up sequence issue due to which leakage current flowing on VDDS_RTC pin on processor.

    Regards,

    Ajay

     

  • 0 in reply to Rajput Ajay
    TI__Guru 62915 points

    You should never connect a voltage source to either of the AM335x USBx_ID pins.  This is a passive analog pin that should only be connected to ground for USB host operation or open-circuit for USB peripheral operation.  Connecting a voltage source to this pin may damage the AM335x device.

    Where did you find a reference that showed this pin pulled up?

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 310 points

    Hi Paul,

    Actually, i realized my mistake for connecting the supply on USB_ID pin. I want to know what should be state or connection of USBx_ID pin if is to be operated as OTG device. We are using USB MicroAB connector for USB OTG.

    Also, can you guide me regarding over problem of 1.8V on VDDS_RTC which becomes 2.4V when processor starts up.


    Regards,

    Ajay

  • 0 in reply to Rajput Ajay
    TI__Guru 62915 points

    The USBx_ID pin should be connected the ID pin of the micro-AB receptacle if your product is going to operate as USB dual-role OTG device.

    If a micro-A plug is attached to the micro-AB receptacle the ID pin will be grounded which indicates the OTG controller should begin operation as USB host.  If a micro-B plug is attached to the micro-AB receptacle the ID pin will be open-circuit which indicates the OTG controller should begin operation as USB peripheral.

    You will need to post a PDF of your power supply schematic and all connections to the AM335x device if you want help with the RTC issue.

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Guru*** 125430 points

    I just ran into a similar issue with another customer (i.e. seeing ~2.4V on VDDS_RTC).  I think the thing that is slightly tricky here is that VDDS_RTC rail requires a 1.8V input, i.e. it is not a dual-voltage option like the VDDSHVx supplies.  So in particular if you have a design where all the VDDSHVx supplies are 3.3V you might be expecting that all the I/O is also 3.3V.  That is almost true with the exception of the pins that belong to the VDDS_RTC rail:

    • EXT_WAKEUP
    • PMIC_POWER_EN (output)
    • RTC_KALDO_ENn
    • RTC_PWRONRSTn
    • RTC_XTALIN
    • RTC_XTALOUT (output)

    So for all of these pins above you need to make sure they always use 1.8V logic.  So if for example you're using the CLK32KOUT signal from the TPS65910A you should be careful about the logic level.  In other words, if VDDIO of the TPS6510A is 3.3V then that means CLK32KOUT will also be a 3.3V signal.  This needs to be translated to 1.8V before connecting to the AM335x.