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THS3061: Is the THS3061 internally protected when not biased?

Carlos Lizandro
Prodigy 20 points
Part Number: THS3061

I have a concern with the THS3061 I am using in one of my designs. In doing a bring up testing, I've noticed that the device preceding the THS3061, actually put out 3.1V into pin 5 of the THS. The THS was not biased at all and I actually measured about 2.45V at pin 7.

So my question becomes, will this 3.1V at pin 5 and seeing 2.45V at pin 7 actually hurt the THS3061 device? will it get damaged?

Thanks

Carlos Lizandro

Systems Engineer

SRT-Group/Bluehalo..

  • 0
    TI__Genius 15521 points

    Hello Carlos,

    I would like to confirm the following:

    1. During lab/bench/PCB testing, the board containing the THS3061 presented a 3.1 volt signal onto the NC (not internally connected) pin 5 of the THS3061.

    2. The THS3061 was not powered on at this time, with the Vs+ and Vs- rails having no signal present.

    3. Without being turned on by power signals at pins 4 (Vs-) and pin 7 (Vs+), the THS3061 began to conduct/turn-on and showed a voltage on Vs+ (pin 7) equal to 2.45V.

    Is this understanding correct?  In summary your design accidentally provided a signal on the NC pin (pin 5) and this resulted in the device turning on with a voltage present on pin 7.

    Were there any input signals present on pins 2 or 3?  Was a voltage measured on pins 2, 3, 4, 6?  Or just a voltage on pin 7?

    Were there any voltages on the other NC pins, being pin 1 and pin 8?

    It is not recommended to design and deploy a system which puts voltage on NC (not internally connected) pins.  If there is a reason to do so based on part evaluation or a pinout difference, it is better to redesign the board for production or on the next revision.

    While there are protection diodes on the supplies of the THS3061, I am concerned about the amplifier's ability to operate normally once a signal is put on the inputs.  If you are able, could you measure and provide information about the voltage seen by the two inputs and one output of the THS3061 when put into your described test condition?

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    Hi Alec. My deepest apologies.It is NOT pin 5, it is pin 3. Very sorry for the confusion.

    Carlos L. 

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    The 3.1V appears at pin 3 of THS3061. Again, my apologies for the erroneous information. 3.1V appeared at pin 3 and measured 2.45V at pin 7. So to rephrase the question, will the THS3061 get damaged under these conditions? No other DC applied at any other pin. 

  • 0 in reply to Carlos Lizandro
    TI__Genius 15521 points

    Hello Carlos,

    I understand better now, thank you for the clarification Carlos.  

    If a large enough signal is placed onto the input or output of an amplifier, it can cause the ESD diodes and input protection circuitry to conduct.  This circuitry is typically tied to either of the power supplies on the IC.  

    By having a large enough input signal on the noninverting input, you would be turning the device on via current paths flowing through the supplies.  

    Do you have power sequencing or various states of operation for this signal chain?  Will the THS3061 ever be "off" during the production use case for the board?

    I am going to check with my team on the potential risk or damage the IC may see if operated in this way.

    Once again Carlos I appreciate your quick updates.

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    This operation was accidental. FYI. it is not the way this IC was intended to function. 

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    And I appreciate you checking with your team. Thanks so much Alec

  • 0 in reply to Carlos Lizandro
    TI__Genius 15521 points

    Hello Carlos,

    I am still working alongside my team on this.  I expect an update by close of business tomorrow.

    Thank you!

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    Thank you Alec...

    Carlos L. 

  • 0 in reply to Carlos Lizandro
    TI__Genius 15521 points

    Hello Carlos,

    If you are observing normal input/output behavior after the incident the particular THS3061 unit may be okay.  Ideally the device behavior is similar to a 'control' device which is not subjected to turn-on via conducting diodes.

    The failure to look out for is if Iq changes from the datasheet specs, or if pins are shorted together that should not be (such as Vin to supply, etc).

    Best,

    Alec

  • 0 in reply to Alec Saebeler
    Prodigy 20 points

    Hi Alec. I usually get notifications on any new posts here. I did not get any until I decided to check and read your response. Thank you kindly for it. 

    What I have observed is that the devices did not appear to get damaged in spite of the fact that they were subjected to a 3.3V at its pin 3 with the device being off. What I am wondering is if there would be a possibility that if during the voltage transition from 0V to 3.3V at pin 3, could have produced a momentary short to ground (device not biased as intended). Another interesting situation I  have observed is that the device driving the 3.3V into pin 3 is another one of your devices: SN65LVDT, has actually gotten damaged. I just noticed from its datasheet that if its inputs are open, and biased at 3.3V (SN65LVDT), its output pin will be held at a logic high and I did measure that. I have a strong suspicion that if the THS3061 might have had a momentary short to ground from its pin 3 when biased at 3.3V (due to the SN65LVDT), that the SN65 might have not being able to handle the short load and gotten damaged in the process. 

    I would like to hear your comments in this regard. Thank you again and please have a great and safe Memorial Day weekend. 

    Carlos Lizandro 

  • 0 in reply to Carlos Lizandro
    TI__Genius 15521 points

    Hello Carlos,

    I can take a look next week after the holiday regarding the overall system effects and ICs.

    Enjoy your Memorial Day weekend too!

    Best,

    Alec