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OPA2677: Overheating on power up

John Provos
Prodigy 20 points
Part Number: OPA2677
Other Parts Discussed in Thread: TINA-TI

The OPA2677 is getting really hot after power up.  I think the part is latching up.  I'm using +-6v power rails and I have 0 volt input and no load.  If I disconnect the thermal pad the problem goes away. I"m using switching power supplies for the rails.

  • 0
    Guru 140200 points
    Hi John,

    is the pad really connected to -Vs of OPA2677?

    Is the ripple of switcher violating the maximum supply voltage rating of +/-6.5V?

    You could take a pi-filter at the supply pins to reduce the ripple.

    Kai
  • 0 in reply to kai klaas69
    TI__Genius 15975 points
    Hi John,

    Were you able to resolve this issue? Would it be possible to attach your schematic to help debug further?

    Best Regards,
    Rohit
  • 0 in reply to John Provos
    Guru 140200 points
    Hi John,

    D3 and D5 are rated for 12V, but OPAMp can only withstand 6.5V. Is this intended?

    You have a coil connected to the output and the OPAmp wired as current driver. The inductance of coil together with C39 can form a sharp resonance which can make the OPAmp oscillate. Do you have any data of the coil? Inductance, winding capacitance, ESR or resonance frequency, so that we can carry out a TINA-TI simulation?

    Can you detect any oscillation or ringing at output of OPAmp with the scope?

    Keep also in mind, that the coil can produce dangerous kick back voltages when shutting off. This can also destroy the OPAmp. Is the coil equipped with a freewheeling diode?

    Kai
  • 0 in reply to John Provos
    TI__Genius 15975 points

    Hi John,

    Because of the current feedback architecture of the OPA2677, I don't think you can include the C39 of 4.7uF in your schematic. Could you de-solder the C39 from your pcb and check whether the heating issue goes away?

    You may want to take a look at the attached article for better understanding of why adding a cap across the feedback results in instability of the amplifier.

    Best Regards,

    Rohit