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TPS7A8300 - Unable to maintain output regulation or program output

JB63
Prodigy 230 points
Other Parts Discussed in Thread: TPS7A8300

Using TPS7A8300 in "any-out" config.  Vin=3.1V, Vout~3V (programmed to 2.8V), load current=500 mA, external on/off control using EN pin.

Output sits at about 3V, but it is programmed to 2.8V.  If I touch some of the pins, I can move this voltage around by a few 10s of millivolts - does not seem stable.

We have a few of these chips in our system.  Some operate fine, while others don't seem to regulate. The ones that are not regulating also do not have any control on output voltage if I change state of programming pins.

Cin= 10uF(ceramic), Cout=30uF(ceramic)

  • 0
    TI__Guru 55940 points
    Hi ,

    Could you provide a bit more information to help debug? For example, a partial layout, schematic, and scope shots of Vin and Vout?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 230 points

    Thanks, Ryan.

    I've attached our schematic and board layout.  All components are on one side of board.  There is a buried plane for Vin and Vout.

    Let me know if it doesn't make it through and I can email it as an attachment.

    Regards,

    John

  • 0 in reply to JB63
    TI__Guru 55940 points
    Hi John,

    Thank you for the e-mail with the layout and schematic. Just as a quick double check only R60 is populated with a 0 ohm resistor on the ANYOUT pins right?

    It is difficult to see, but is the device ground only connected through vias to the rest of the board ground?

    Also, could you provide a scope shot with Vin, Vout, and Ven at startup?

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 230 points
    Yes, R60 is 0 ohm.

    There is a buried ground plane and there is also a ground pour on the component side. Yes, the package is grounded on the underside and ground pins like 8, 18 and 21 are tied into this pad for the connection to the plane.

    Working on getting the scope shots....
  • 0 in reply to JB63
    Prodigy 230 points

    Ryan,

    Here is another interesting bit of info.

    With Vin currently at about 3.1V, I noticed that changing the level of EN line from 3.1V to 1.7V causes the output level to also drop from about 3V to about 2.6.  Neither of which is the programmed 2.8V, but should the voltage level on the EN pin have this affect on Vout?

    Is there some level restriction on the EN pin drive that is related to VIN?


    John