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AM3358: Custom board bring up issue

Samer Abbas
Expert 1055 points
Part Number: AM3358
Other Parts Discussed in Thread: TPS65217, , LMR33620, SN74LVC1G07

Hi,

I have a 2nd Rev of custom board based on BBB and having trouble booting it up. Previous rev would boot up fine but this one is not booting up at all. I don't see "CCCC" on UART. I am getting all voltage rails from TPS65217 and all their values are correct.

LDO1=1.8V

VSYS=VAC=5V

LDO2=3.3V

I have looked at all the checklists and AM335x board bring up tips but can't figure it out.

On AM3358 OSC0_OUT, I am getting 10.5~11.2 MHz frequency.

What could be the issue here?

Thank you

  • 0
    TI__Guru* 87850 points

    Samer, the oscillator frequency needs to be corrected.  Review section 6.2.2 of the datasheet to ensure you are meeting all of the requirements for the input crystal and schematic.  Compare this with the working board.  Be sure to also compare layout differences.   Also be sure to check proper power on sequencing and voltage on VDDS_OSC.  If possible, set SYBOOT[5]=1 to enable CLKOUT1 to output after power up and check its frequency.  This should reflect a square wave clock at the frequency of the crystal if everything is working correctly.

    Once this is corrected, then you should move on to other issues if there are any.  

    Regards,

    James

  • 0 in reply to JJD
    Expert 1055 points

    Hi James,

    I am getting 24MHz at CLKOUT1. I also compared my previous Rev and current Rev oscillator schematics and layout and they are similar. What else could be causing it to not boot from SD card?

    Thank you

  • 0 in reply to Samer Abbas
    TI__Guru* 87850 points

    Can you probe the CLK on the SD card interface while booting.  Do you see a valid clock during boot?  Check proper voltage to the card.  What is your boot sequence?  Do you have JTAG connection on your board?  Are there any other major differences on the 2nd rev?  Different DDR or other different connections?

    Regards,

    James

  • 0 in reply to JJD
    Expert 1055 points

    Hi James,

    I don't see any clock on CLK of the SD card. I just see 3.3V. My boot sequence is similar to beaglebone, which is similar to my previous rev and it looks for SD card right away.

    I do not have JTAG.

    The major difference was to add two stages of a pre-regulator LMR33620. First stage converts 24V to 12V. Second stage converts 12V to 5V, where 5V goes to TPS65217.

    This part of circuit was tested as a separate piece with the previous rev and it worked fine. 

    On this rev, all the rails of TPS65217 seem to be fine but maybe board is stuck at some other source for boot?

    Thank you

  • 0 in reply to JJD
    Expert 1055 points

    One other thing I noticed is that my NRESET_INOUT is also at 0.16V, even though my PMIC_PGOOD and VIO both are 1.8V. What could be causing NRESET to stay low?

    Thank you

  • 0 in reply to Samer Abbas
    TI__Guru* 87850 points

    It seems like there is a conflict on NRESET_INOUT.  Is there something else that can drive NRESET_INOUT?  Typically you should see NRESET_INOUT stay low for a short time after PORz (PMIC_PGOOD) goes high, and then it will go high and stay high.  If it doesn't, something other than the processor is driving it low.  Or possibly there is no pull up on the signal, which is required to keep it high.

    Regards,

    James

  • 0 in reply to JJD
    Expert 1055 points

    James,

    Really appreciate your help!

    I got it working. The buffer holding down NRESET_INOUT was supposed to be SN74LVC1G07DCKT but in this rev SN74LVC1G06DCKT got populated, which is opposite of SN74LVC1G07. I replaced this buffer from an older board and my board turned on.

    Thank you