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THS3095: OP-Amp not working with dual supply votlage

Sai Sandeep Lolla
Prodigy 30 points
Part Number: THS3095
Other Parts Discussed in Thread: TPS65131,

Tool/software:

Hi,
I intend to amplify a signal using THS3095DDA. I am using the same circuit as the evaluation board of THS3095 (THS3095EVM Evaluation board | TI.com):

except without any capacitors present on the evaluation board. 
I use TPS65131EVM-839 Evaluation board | TI.com to generate a +12/-12V dual supply that is the dual power supply for the opamp. The input to this board is 5V.

So EVAL_TPS65131 is the power supply to a THS3095DDA IC mounted on a SOIC14 adapter and placed on a breadboard. Resistors with the same value as in the EVAL_THS3095 are connected to the op-amp in the breadboard. I also have THS3095EVM Evaluation board | TI.com. When I connect these two evaluation boards, everything works fine and I see an amplified square wave as intended. 

The problem is when I connect the +12/-12V dual supply to the op-amp on the breadboard. As soon as I enable the op-amp the supply current continuously rises more than 40mA @ +12/-12V supply to the op-amp and the chip starts heating up. 

The weird thing is when I connect the op-amp to a single-ended supply i.e. to +12V/0V, there is no problem and the same chip(op-amp) that heated up now also amplifies the signal without any problem. Is there a grounding problem somewhere, what could be the problem such that a single supply works and dual supply does not? 

Thank you in advance!!

PS: The thermal pad of the chip is left floated since it cannot be soldered on a SOIC14 adapter pcb

  • 0
    TI__Mastermind 18045 points

    Hi Sai,

    There are a couple options we have to debug and get to the source of the problem. One question I have is if you are seeing the same issue with the THS3095EVM from TI as well when you force +/-12V from the TPS65131. I do not think the Powerpad itself is causing any issue as it can be set to any potential. 

    Best regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 30 points

    The following are the scenarios I have debugged:
    1. Connected +12/-12V to THS3095EVM -> works good, I see an amplified signal without any heating up or extra current consumption 
    2. Connected +12/-12V to THS3095 on a breadboard with 100nF and 22uF decoupling caps across the supple rails ->the decoupling caps did not help. The same situation as before happened. Heating up of the IC, very high current consumption. It's as if there is a short circuit. The input supply to the TPS65131EVM-839 Evaluation board | TI.com drops from 5V to 2.5V with very high current consumption.
    3. Connected +12/-12V to THS3095 on a breadboard without the 1kohms feedback path -> no heating or extra current consumption 

    So there should be a problem with the feedback, maybe??. But I measure 1kohms between pin 2(IN-) and pin 6(OUT) of THS3095 with a multimeter.  

  • 0 in reply to Sai Sandeep Lolla
    TI__Mastermind 18045 points

    Hi Sai,

    My first suggestion would have been to add decoupling to the breadboard, but it seems like that was already done and did not help. Could you probe the output of the amplifier and see if you see any signal? This would include adding the Rf back to the circuit and basically probing the circuit with the same setup as the one on the EVM. You can add a 1V input signal to the noninverting pin and ideally the output should be around 5V. This would be a good test to see if the device is configured appropriately. Having a feedback resistor should not be causing this either as it is ideal. Have you also tried a new device to use on your breadboard circuit? ESD damage can sometimes cause the behavior you are experiencing as well.

    Best Regards,

    Ignacio