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OPA454: Alternate P/N

HARI T O1
Expert 1215 points
Part Number: OPA454
Other Parts Discussed in Thread: LMC662, OPA462, OPA455

Dear Team,

We are using OPA454 for one of our Project.

Due to the wrong connection, the component got damaged.

OPA454 is not available with any vendor. Could you please suggest an alternate P/N which is pin-compatible with OPA454?

Below is my circuit.It contains LMC662 also but it is not damaged.Hope I can use the same device.May I know your thoughts about this.

 

I tried with OPA462 but my output is coming as shown below. I don't know why the DIP is coming in the output

Regards

HARI

  • 0
    TI__Guru* 93105 points

    Hello Hari,

    Sorry to hear about the problems obtaining OPA454 devices.

    The two devices that can drop into the OPA454 board space are the OPA462 and OPA455. There are some electrical difference between the OPA454, OPA455 and OPA462, but they probably aren't going to be so different that your circuit won't operate as expected. The OPA455 and OPA462 are the extent of what TI has that provides high-voltage capability, in that particular package and functional pinout. 

    That momentary -0.6 V spike  result your obtaining within the first 50 us of power on, start-up with the OPA462 may, or may not, be a real behavior. That would really need to be verified on the bench using your exact circuit. You do have a complex circuit with the additional feedback loops from the LMC662A output, back to the OPA462 supply lines. There is the relatively high 4.7 nF capacitor across the LM662A supply pins that must be charged as well as other capacitances in the circuit. Start-up conditions can certainly be different than what is obtained when the circuit has come to steady state operating conditions.

    There is the possibility as well that the OPA462 and LMC662A simulation models don't accurately reflect what the actual devices do in those initial first moments of start-up. The simulation models are complex and include a lot of the op amp behaviors, but they are still simplifications of the actual devices. Therefore, they might not behave exactly the same in simulation at start-up as the real products do in an actual circuit. That is why it is important to observe the actual start-up behavior on the bench if that is a concern.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Expert 1215 points

    Hi Thomas,

    Thank you very much.

    I will order OPA462 and OPA455 and will test in the bench and let you. (It will take at least 2 Weeks)

    May I know your opinion about the circuit which I shown?.This is used to measure the voltage of a charge pump present in our 

    ASIC.The Output impedance of charge pump is in Giga ohms.

    Regards

    Hari

  • 0 in reply to HARI T O1
    TI__Guru* 93105 points

    Hello Hari,

    Any op amp including the OPA454, OPA455 and OPA462 will require some level of input bias current Ib. The total Ib is determined by the bias current required by the input bipolar transistor or FET, and the leakage current of the ESD cell connected to that input. These three high-voltage op amps have FET inputs and low-leakage current ESD cells so their Ib is typically in the range of tens of picoamperes at 25 C. Despite the low Ib it could present a significant load to a Gigaohm source impedance. 

    Your circuit is optimized in that the only load on the Gigaohm charge pump output is the non-inverting input of the high-voltage op amp. It avoids other circuitry that could add additional load to the charge pump. I suppose you will just have to see how the op amp performs in the application.

    One item often overlooked in very low current applications is PC board leakages due to residual solder flux remaining after cleaning. It can be quite difficult to remove all the flux and it can act as leakage resistance loading the very high impedance source. Just be aware of this possibility if the circuit doesn't appear to operate exactly as expected.

    Regards, Thomas

    Precision Amplifiers Applications Engineering 

  • 0 in reply to Thomas Kuehl
    Expert 1215 points

    Hi Thomas,

    Thank you.

    I ordered the components yesterday. We will get it within two weeks.

    I will update you after testing.

    Regards

    HARI

  • 0 in reply to HARI T O1
    TI__Guru* 93105 points

    Hello Hari,

    I hope all goes well with your OPA455/OPA462 tests. Since it will be a couple of weeks until you have results, would you mind closing this thread? Otherwise, it remains open but inactive. If you find you have more questions after you obtain your results you can always open a new e2e.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • +1 in reply to Thomas Kuehl
    Expert 1215 points

    Hi Thomas,

    Sure we can close this question.If any help required I will reopen again.

    Regards

    HAri