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Original question:

OPA2863A: OPA2863A

OPA2863: OPA2863 testing issue in replacing LMH6643

Gary Teng
Genius 5900 points
Part Number: OPA2863
Other Parts Discussed in Thread: LMH6643,

Hi Sir,

 Customer want to replace LMH6643 by using OPA2863 due to LT question. They test sample and buy a reel OPA2863 for replacement test but have high failure rate / burn out issue.(Failure rate:10% in testing 100pcs OPA2863)

1. There's noise on output: comparing with LMH6643 or goot OPA2863, there's larger noise at output. After 4 stage, the output noise will become a square waveform.

2. Some failed device has impedance issue at pin 3

Customer want to know 

1. Is there any application limit on using OPA2863 to replace LMH6643?

2. Any other suggestion if OPA2863 is not a good solution?

Thanks for your kindly help.

Best regards,

Gary Teng

  • 0
    TI__Mastermind 24379 points

    Hello Gary,

    I do not currently see a reason why the LMH6643 cannot be replaced by the OPA2863 if desired by the customer.

    I would like your help clarifying a couple items about your post:

    1. Is the circuit image you provided the whole circuit?  I see a mention of "after 4 stage.."; is this a discussion of multiple OPA2863 stages or multiple tests or timestamps?

    2. As I understand it, using the OPA2863 as a drop-in replacement for the LMH6643 has resulted in failures/burn out.  The issue appears to show symptoms via a low impedance measurement on the VIN+ pin.  Are there any other symptoms or details regarding the OPA2863 you can share?

    3. Could you provide component values & voltage/current signal levels based on the image you provided?  I would like to know the voltage or voltage range produced by the piezoelectric device as well as the gain and voltage divider settings (via the resistor values).

    Thank you for your time and input.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Genius 5900 points

    Hi Alec,

     We see there's around 2V input at IN+- pin but didn't know the frequency about the piezo device. Will let you know if we get some other information fromc customer.

     And, customer use 2 LMH6643/OPA2863 for 4 stages process, but only found damage at first stage of OPA2863. FYI.

    Regards,

    Gary

  • 0 in reply to Gary Teng
    TI__Mastermind 24379 points

    Hello Gary,

    Thank you for the update.  I will look out for additional information; for now I am considering your new information.

    Best,

    Alec

  • 0 in reply to Gary Teng
    Guru 48395 points

    Hey Gary, the obvious next thing are the RC values in the circuit and what the loading is, very likely the stage burning out is oscillating, 

  • 0 in reply to Alec Saebeler
    Genius 5900 points

    Hi Alec,

     Anything I have to provide for your reference in the case? 

     Those waveforms below are about OP input / output. Ch1/2/3: Pin 1/2/3

    Good unit voltage at pin 1/2/3 is 2.45/2.47/2.53V

    NG unit those impedance on pin 2/3 is not 0ohm.  voltage at pin 1/2/3 is 3.9/3.89/2.68V

    Thanks for your kindly help.

    Regards,

    Gary

  • 0 in reply to Michael Steffes
    Genius 5900 points

    Hi Michael,

    Do you think there's different impedance value in LMH6634 and OPA2863 input and cause different oscillating result?

    Regards,

    Gary

  • 0 in reply to Gary Teng
    TI__Expert 8710 points

    Hi Gary, 

    The input capacitance, bandwidth, and compensation of each amplifier can all affect the stability of a circuit. If you can provide the resistor and capacitor values we can simulate to see if it is stable. 

    The waveform certainly looks like an oscillation, but the low impedance between the input and ground suggest an electrical overstress event that damaged the ESD diode between the input and VS-. Any more information you can share would be helpful. 

    Regards, 

    Jacob