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Original question:

OPA564: Question about sequencing of power supplies

OPA564: Power supply sequencing

Stanislav Husar
Prodigy 40 points
Part Number: OPA564

Hello,

I have a question about power supply sequencing for power opamp OPA564. I would like to run the opamp from a single supply. I actually do not need its digital functions. However datasheet says explicitly, that digital supply must always appear before or with main supply.

How should I connect it? This has been answered already, however unfortunately I can no longer access evaluation module proposal.

Thanks in advance,

Stanislav

  • +1
    TI__Guru 52161 points

    Hi Stanislav,

    Stanislav Husar said:
    How should I connect it?

    Regarding to the digital power, you can connect a zener with the single supply rail (do not use the large decoupling capacitor at the zener's output), that should meet the power on/off sequences as specified in Figure 36 of the datasheet. 

    Stanislav Husar said:
    unfortunately I can no longer access evaluation module proposal

    Please see the attachment. 

    sbou219.pdf

    Please let me know if you have additional questions. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 40 points

    Hello Raymond,

    Thanks for your reply. I did a few simulations in LTSpice. Zener really can track main supply rail as it starts. However once I add any decoupling, even 1nF causes a delay of a few microseconds. Is it okay to omit decoupling at all? Or can the op-amp tolerate this delay?

    Thanks in advance,

    Stanislav

  • +1 in reply to Stanislav Husar
    TI__Guru 52161 points

    Hi Stanislav, 

    You may omit the decoupling capacitor. If you want to have the same supply ramp, then it will be the best to remove the decoupling capacitor. 

    Stanislav Husar said:
    can the op-amp tolerate this delay?

    I do not have the hard data about the min. of delay on the Vdd rail vs. analog supply. Since you do not use the digital logics, then it should not make any differences, as long as the OPA564 is power up/down properly per the datasheet requirements. 

    If you have other questions, please let me know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 40 points

    Hello Raymond,

    So I can simply omit Vdd decoupling, feed zener from main supply, and it should work. That settles it then.

    Thank you for help.

    Stanislav