AD719x reference buffer amplifier?

Hi all,

what is a suitable amplifier to be used as a reference buffer for a AD719x (AD7190, AD7192)?

Since the reference input of the AD719x draws rather high peak currents, it has to be an amplifier with a quick settling after going out of regulation, correct?

Therefore I'm asking for a proven amplifier.

TIA,

Oliver

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  • Jonathan,

    the 7uA average current is not a problem for most amplifiers, but the transient current is, as I explained above.

    Therefore "low output impedance at lower frequencies" is not relevant, but tolerance to transient loads is.

    You mention the AD8031 being proven with the PulSAR ADCs. Well, the AD7690 data sheet is funny (kind of): Of course it mentions the AD8031, but it also claims 10uF decoupling at Vref (you know why?).

    But the AD8031 data sheet allows not even 10pF at G=1, so please tell me how this can work and/or what the dashed line between AD8031 output and REF in Fig. 33 of the AD7690 data sheet means.

    AN-931 also doesn't reveal the solution but raises more questions: It mentions "Now [...] the buffer (op amp) data sheet advises avoiding heavy capacitive loads. However, the PulSAR ADC requires a 10 μF or larger reference decoupling capacitor (REF CAP). These two requirements seem at first to contradict each other." Well, I don't see AN-931 providing a solution to this contradiction.

    It tells me to place 10..22uF as near as possible at the Vref pins, it tells me that the the amplifier data sheet "advises avoiding heavy capacitive loads", and then?

    Oliver

Reply
  • Jonathan,

    the 7uA average current is not a problem for most amplifiers, but the transient current is, as I explained above.

    Therefore "low output impedance at lower frequencies" is not relevant, but tolerance to transient loads is.

    You mention the AD8031 being proven with the PulSAR ADCs. Well, the AD7690 data sheet is funny (kind of): Of course it mentions the AD8031, but it also claims 10uF decoupling at Vref (you know why?).

    But the AD8031 data sheet allows not even 10pF at G=1, so please tell me how this can work and/or what the dashed line between AD8031 output and REF in Fig. 33 of the AD7690 data sheet means.

    AN-931 also doesn't reveal the solution but raises more questions: It mentions "Now [...] the buffer (op amp) data sheet advises avoiding heavy capacitive loads. However, the PulSAR ADC requires a 10 μF or larger reference decoupling capacitor (REF CAP). These two requirements seem at first to contradict each other." Well, I don't see AN-931 providing a solution to this contradiction.

    It tells me to place 10..22uF as near as possible at the Vref pins, it tells me that the the amplifier data sheet "advises avoiding heavy capacitive loads", and then?

    Oliver

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