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DAC8411: Oscillation of DAC when capacitor on output

Gerhard van Rensburg
Intellectual 400 points
Part Number: DAC8411

I have a Ferrite Chip Bead in series of the DAC8411 output, with a 100nF capacitor to GND, to form a LC filter.

Ferrite bead is 1500OHM @ 100MHZ. (HZ0402A152R-10)

The DAC8411 has a 100KHz Oscillation on its output, with the Capacitor connected. Nothing else is connected.

Shorting the Ferrite does not help at all, the oscillation is still there.

Is there any reason why this could happen?

Using a 1.5K Resistor and 100nF Cap works as a RC filter, but with the ferrite and Cap, the DAC oscillates.

The ferrite bead by itself, without the filter capacitor, also seams fine.

Any help appreciated

  • 0
    TI__Guru 52663 points
    Hi Gerhard,

    The output of the DAC8411 string is internally buffered with an amplifier (see figure 74 in the datasheet), as such it can have issues with stability when there is a large capacitive load on the output. In fact if you look in the specification table of the device (pg 5) there is a specification called 'capacitive load stability' which is rated at 1000pF. Your load, 100nF, far exceeds that limit. When you add a series resistor to the output you isolate the output from the capacitor, which allows the internal amplifier to see a much smaller capacitive load.

    I would recommend you stick with the RC or buffer the output with an amplifier that can handle are large capacitive load.

    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    TI__Guru 52663 points
    Please mark 'This Resolved My Issue' if you have no more questions in regards to this issue.

    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    Intellectual 400 points

    Resolved by removing the Capacitor.

    Thanks