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DAC8771: Using VNEG_IN to supply power to external components, including the OPA192 operational amplifier and the DG468 analog switch

Neus Pons
Prodigy 10 points
Part Number: DAC8771
Other Parts Discussed in Thread: OPA192, , TLV9362, OPA2990, DAC8775,

Tool/software:

Hi,

I’m working with the DAC8771 and would like to use its internally generated negative supply (via the integrated charge pump) to power external components—specifically one OPA192 operational amplifier and one DG468 analog switch.

I couldn’t find any specifications in the datasheet regarding the use of this negative rail to supply external circuitry. Could you please clarify whether this is supported, and if so, what the maximum current that VNEG_IN can safely source or sink to external components is?

Thank you very much for your support.

Best regards,
Neus

  • 0
    TI__Guru* 97465 points

    Neus,

    I know that there have been others that have used the internal buck-boost to drive external circuitry, but we haven't characterized the device in this way. Looking at the 4-channel version (DAC8775), I have seen at least one case where the device had a hard time starting up at higher temperatures when loaded with the TLV9362. These op-amps, at two for each channel, would cause problems for the buck-boost. When these op-amps were replaced with the OPA2990, I think these problems were removed. 

    For the OPA192, the operating current is higher than the OPA2990, so I'm not sure how different the startup current profile would be from one device to the next. You would also need to consider the bypass capacitors for each op-amp as part of the load. Regardless, this is what you'd need to consider using the internal buck-boost to drive other devices.

    If you're interested in testing it, I would consider getting a DAC8771EVM and setting it up to power an op-amp. This would be a good test for this application.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru* 97465 points

    Neus,

    Incidentally, this is the post that I had been referring to: 

    https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1443512/dac8775-buck-boost-converters-not-starting-at-elevated-temperatures

    Again, let me know if you have any further questions.

    Joseph Wu