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REF3112 Vout is oscillating

Harald Styrsky
Prodigy 30 points
Other Parts Discussed in Thread: REF3112

Hi,

we have a REF3112AI on our Micro Controller Board. Some boards show a oszillating output voltage at Vout (kind of saw tooth, about 10kHz); measured directly an C102. Decreasing the value to 2.2µF (or removing completely) solves the problem.
Sometimes there is a temperature dependency.

See our design:

My questions are:

1) What is an optimal value for C102?
The datasheet tells 1µF - 10µF, but 10µF seems to be to much.

2) How sensitive ist the device with a supply of 1.8V at Vin; what tolerances are allowed?
Might this be a problem too?

Thank you for the help,
Harald

  • 0
    Genius 3295 points
    Hi Harald,

    Your schematic does not appear to have attached (use "rich formatting" and the "link" or "attach" function).

    What is the load on the device?

    What kind of capacitors are you using?

    The device is capable of working at 1.8V, with 5mV of dropout.

    Mike T.
  • 0 in reply to Mike Tripoli
    Prodigy 30 points

    Hi Mike,
    the REF3112 is only connected to tha ADC reference input of an micro controller (xilinx zynq XA7C020).
    We use automotive ceramic SMD capacitors (X7R AEC-Q200).

    We took the proposal out of the Xilinx documetation (data sheet "UG865 (v1.4) June 11, 2014" page 78, chapter "Application Guidelines");

    I attatched screenshots from our schematics and xilinx docu (hope you can see them now).

    Can REF3112 provide a proper output with an input of 1,7V (which is 1.8V -5% tolerance) like it is shown in Xilinx application:

    /Harald

  • 0 in reply to Harald Styrsky
    Genius 3295 points
    Hi Harald,

    1.7V is on the hairy edge of "5%". If it were me, I'd "find" a higher voltage to power the device. Why not use the 3.3V available?

    I would also do two things:

    1.) Put an additional input cap on the order of 10µF on the input.

    2.) Though the data sheet says the device is stable with "with any capacitive load" the simplified diagram shows an opamp on the output. Opamps generally do not like large capacitive loads on their outputs. I'd add a 10-100Ω resistor between the output and the caps and see if that doesn't take care of it.
  • 0 in reply to Mike Tripoli
    Prodigy 30 points

    Hi Mike,

    thank you for the hints; we will consider them for the next HW release.
    For the moment we change the capacitor value down to 1µF - this runs well in practice.

    I think we can close the thread at this point.

    By,
    Harald