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PGA970EVM: PGA970EVM - Defective OPA1662?

Gabriel Calin
Intellectual 300 points
Part Number: PGA970EVM
Other Parts Discussed in Thread: OPA1662, PGA970, OPA350

Good afternoon everyone,

I got a PGA970EVM a few days ago and I found a strange behavior with the OPA1662 output driver. Although it shows a sine signal output when without load, almost any connected load will zero the output (behavior similar to a shortcut). Investigating the board I notice the OPABIAS reference voltage has a strange 8.45V (the board is supplied with 24V) and the OPA1662 temperature is above 40C, even without any connected load.

Everything points to a fault OPA1662, however I decided to post a message just to check if anyone had a similar issue with PGA970EVM boards,

Gabriel Calin

  • 0
    TI__Mastermind 31655 points
    Hi Gabriel,

    That is unusual. OPABIAS should be about 12V with a 24V VPWR to the EVM. If you bypass the external amplification stage (J2 and J7 set with pins 2 and 3 shorted) does the waveform output behave as expected even with a load attached?

    Were you able to determine if it was just one of the OPA1662 channels that is malfunctioning, or are both of them?

    Regards,
  • 0 in reply to Scott Cummins
    Intellectual 300 points

    Hello Scott,

    Connecting directly to the PGA970 (bypassing the OPA1662) works fine with my load (I connected a 700ohm).

    I did some other tests and both OPA1662 channels appear to be malfunctioning when the load is connected. What is very odd is the OPA1662 output, without load, looks good. No visible noise, distortions or anything that would indicate a problem can be detected. When the load is connected, the output zero and the IC starts heating up. In this conditions the OPABIAS also starts drifting a little, reducing the voltage as the IC heats up. I checked all the passive and board mounting for any misplaced components or soldering problems. All appears to be good, so I guess the OPA1662 is the problem.

    I would replace the OPA1662 is I had any in stock. The closest I have is a OPA350, however it cannot handle the 24VDC power supply.

    Is it possible to get a replacement board or a spare OPA1662 for a testing?

    Regards,

    Gabriel Calin,

  • 0 in reply to Gabriel Calin
    TI__Mastermind 31655 points

    Hi Gabriel,

    It does seem like a problem with the OPA1662. If you would like a new PGA970EVM I recommend submitting a return on the one that you have. However, if you just want to try replacing the OPA1662 you can get some free samples from the TI store.

    Regards,

  • 0 in reply to Scott Cummins
    Intellectual 300 points

    Hello Scott,

    Returning the board would be prohibited expensive since I am in Brazil (the RMA export paperwork is insane). Would be cheaper (and much faster) to scrap the board and buy a new one.

    As for the sample, TI apparently store does not allow samples to be sent to Brazil anymore. I just tried now and it returns "Your cart contains more items than is allowed. Please limit your cart to 0 items." (see below).

    Could you arrange a new OPA1662 to be sent for testing? Or somehow unlock TI sample cart?

    Best Regards,

    -- 
Gabriel Calin
----------------------------------
Metrolog Controles de Medição Ltda
Rua Sete de Setembro, 2656  -  Centro
13560-181 São Carlos - SP - Brasil
Fone +55 (16) 3371-0112
Fone +55 (16) 3372-7800
Website: http://www.metrolog.net
Email: gabriel.calin@metrolog.net

  • 0 in reply to Gabriel Calin
    TI__Mastermind 31655 points
    Hi Gabriel,

    I'll get some samples sent to you at the address you listed.

    Regards,
  • 0 in reply to Scott Cummins
    Intellectual 300 points

    Hello Scott.

    Thank you. I appreciate your support.

    I will let you know how it goes when the replacement OPA1662 arrives.

    Best Regards,


    Gabriel Calin

  • 0 in reply to Gabriel Calin
    Intellectual 300 points
    Hello Scott,

    Just replaced the OPA1662 and it is working as expected.
    Thank you for your support.

    Best Regards,

    Gabriel Calin