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TPS65217: TPS65217C power up issue

Francis Kimpel
Prodigy 30 points
Part Number: TPS65217
Other Parts Discussed in Thread: AM3358

We are experiencing a power up failure on a board design that incorporates a TPS65217C powering up an AM3358 processor.(Beaglebone based design)

This board  powered up previously with no issue and we were able to boot the AM335x processor and run our application from Flash.

Using an oscilloscope we captured the LDO Input voltage and LDO1 output when power is applied to the TPS65217C

Scope channel 1: Triggered on the LDO and DCDC INPUT VOLTAGE source (+3.3V in our system). Rise time ~ 1 ms

Scope channel 2: Monitored the LDO1 output and noticed that it didn't attempt to turn on until 50 ms and at 50 ms it turn on to to .07V(instead of 1.8V) for about 5 ms and then turned off.

Connections:

The connections to the TPS65217C follow the recommended connections shown in TI SLVU5511 for interfacing a TPS65217C to an AM335X processor except for 1 condition I noticed in the datasheet. 

The DCDC converters and LDO inputs are not powered by the SYS pin -instead they are powered by an external +3.3V supply.

Also should be noted that

1. The Battery and USB inputs are not used and are not connected

2. The AC Input has +5V connected to it. The SYS1,2 output pins are not connected.

While the data sheet states that the DCDC inputs must be connected to the SYS pin, It doesn't stipulate this for the LDO inputs.

What do you think would cause the LDO1 output to delay 50 ms before attempting to turn on ?  It only supplies the VDDDS_RTC and VDDS power for the AM3358 in this design.

Keep in mind that it was originally working.

thanks,

Frank Kimpel

  • 0
    TI__Intellectual 1990 points

    Hi Frank,

    Thanks for the post! We are currently looking into this. Did you paste a scope shot? If so, it seems the scope shot didn't make it to the post. Could you try to reattach the scope shot by using the "insert function" (see below)? Let me know if there are any questions.Thanks!

    Regards,

    Paul Kundmueller

  • 0
    Prodigy 30 points
    Paul
    Since the last post I discovered the following:

    The LDO1 output into the VDDS pins of the AM3358 processor is measuring 2 ohms to ground. The LDO1 output doesn't go anywhere else.

    The VDCDC3 output into the VDD_CORE of the AM3358 processor is measuring 1.4 ohms to ground

    Removed all capacitors from the LDO1 output net and short remained.

    Something caused my AM3358 processor to get damaged. Not sure what it is.
  • 0 in reply to Francis Kimpel
    TI__Intellectual 1990 points
    Hi Frank,

    Thanks for the follow up! Hopefully that is the root cause. Let me know if there is anything else we can help you with.

    Have a good weekend and happy debugging,

    Paul Kundmueller