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OPA564 digital flags....

Other Parts Discussed in Thread: OPA564

If I do not use the flags on the OPA564, can I just leave the power supply for the flags unconnected? Is this a bad idea?

  • Andrew,

    Since the digital power supply controls NOT only thermal shutdown and short-circuit current flags but ALSO Enable/Shutdown function of OPA564, it MUST be powered by Vdig between +3.0V and 5.5V referenced to negative supply, (V-); see specified voltage for digital below.

  • Even if I leave the E/S pin unconnected, I still need it?

  • Andrew,

    Leaving an E/S pin open, will not make a difference since the internal pull-up resistor will not be able to satisfy the enable mode requirement, (V-)+2V<Ven<(V-)+Vdig, when Vdig is floating.  In order for the digital control circuitry of OPA564 to work, including Enable/Shutdown function, it must powered by Vdig - see discription for Vdig below.  The valid range for Vdig is from ((V-)+3V to (V-)+5.5V - it CANNOT be left unconnected.

  • Thanks!

    I ask because we got it to work on our first design. However, some of the time, the circuit would mysteriously not work (approx 10% of the time out of a sample size of 100).  We are doing the redesign, and we found that now none of them work to the full potential on our bread boards unless we use the Vdig pin.  It clarifies why the new designs on our bread boards do not work, but I am kind of worried now because the older designs work to the full potential without  it. Sort of funny but kind of scary at the same time. Was there a die change or something? Maybe that explains the difference. 

  • I do not believe there was any recent revision to OPA564 die.  It's hard to believe that the circuit would work with Vdig open but depending on the enable function internal current leakages it is feasible that it could happen. However, such operation does NOT meet the PDS requirements and thus is NOT recommended.

  • Thanks!

    Would it be viable to just use a voltage divider from the negative rail to power vdig? 

  • Using a resistor divider to power OPA564 Vdig is NOT recommended but it should crudely work as long as you chose proper resistor values to assure Idig quiescent current of at least 100uA in addition to any current being sunk or sourced by current limit and thermal shutdown flags.  Also, you must make sure that as the main supplies come up, the voltage on Vdig does NOT violate even momentarily the voltage range of (V-) to (V-)+5.5V

     

  • So...what happens when you violate the Vdig rules...does it by, any chance, burn the chip badly?

  • Exceeding the maximum voltage on OPA564 Vdig of (V-)+5.5V, even momentarily, by more than few hundred millivolts may permanently damage the IC. Thus, if this is possible to occur, you must use an external clamps to prevent this from happening.

  • Is it possible we can talk over email or phone? We are having huge issues with this chip. I am not sure if it is the board design, the circuit design, or just the chip itself.

    Thanks

  • Andrew,

    You may email me at: lis_marek@ti.com
  • Hi Marek,

    Would you recommend using a Zener diode instead of a resistor voltage divider for Vdig? Or could you please make any reference to a document to supply this Vdig the best way? Thank you!