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DAC8571: Low power and fast settling

Shuji Ishiwata
Mastermind 7825 points
Part Number: DAC8571

Tool/software:

Hi All,


I have a question about low power and fast settling.

If the low power mode is selected at startup, the output will oscillate if it is set to 0V.

However, in fast settlingmode, it does not oscillate.

There are individual differences depending on the device.

Please tell me the difference between low power and fast settling modes.

Also, why does it oscillate in low power mode?


Best Regards,
Ishiwata

  • 0
    TI__Mastermind 42083 points

    Hi Ishiwata-san, 

    Are you evaluating this device on a custom board and seeing the oscillation in the low power mode? If so, can you share your schematic with an oscilloscope waveform of the startup oscillation in low power mode, and no oscillation in fast settling mode?

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Mastermind 7825 points

    Hi Katlynne-san,


    Thank you for your reply.

    I would like to send the circuit diagram via private message because it is confidential information. Is that okay?

    I have also confirmed oscillation in low power mode. There is no oscillation in fast settling mode with the same circuit.

    I think that placing a resistor and capacitor in parallel in the feedback path could prevent oscillation, but what would be a good constant?

    Please give me some advice.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 42083 points

    Hi Ishiwata-san, 

    I saw you sent your schematic. I'll review and get back to you. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Mastermind 7825 points

    Hi Katlynne-san,


    Thank you for your support.

    We explained the following to the customer, and they understood.


    " It is likely that when the phase margin is low power mode, the response is slowed to reduce current consumption.
    For that reason, it is likely that switching to fast settling mode improved the responsiveness and improved the situation.
    We think that oscillation occurred due to individual differences in devices and a large step change in input.
    "

    It is likely that there is no phase margin in low power mode due to individual differences in devices.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Mastermind 42083 points

    Hi Ishiwata-san,

    Does the oscillation start after you pull the OD of the XTR low? Or was there some command sent to the DAC at this time as well?

    The input to the XTR is just an amplifier so I still wouldn't expect oscillations in either mode.  

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Mastermind 7825 points

    Hi Katlynne-san,


    Thank you for your support.

    It has been reported that oscillation also occurs when the XTR OD is set to Low.
    The DAC setting is also set to 0mV.

    It has been reported that the phenomenon can be reproduced due to individual differences.
    It is not expected to oscillate, but there are devices that do oscillate.

    The customer resolved the issue by changing to fast settling mode.

    Best Regards,
    Ishiwata