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THS4631 heating up

iAdrian
Prodigy 110 points
Other Parts Discussed in Thread: THS4631

Hello,

I am using a THS4631 with +/-12V supply connected in a non-inverting configuration with a gain of 6 V/V (Rf = 5k, R1 = 1k).  I am using an input voltage of 1V.  As soon as I power up the circuit, it begins heating up.  What could be the reason for this?  I also tried connecting the opamp as a buffer, with the same 1V input and it also heated up.  I tried 5 different opamps (soldered on a small pcb breakout board with pins) and they all behaved the same.  

Thanks

  • 0
    TI__Genius 15975 points

    Hi Adrian,

    Are you using the same EVM provided from TI or is it your customized PCB? What is the supply current measured?

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Prodigy 110 points

    I'm using an adapter board to be able to connect the SOIC package in a breadboard.  I have an open load (no RLoad or CLoad).  The supply is delivering 15mA which corresponds to the max Iq in the datasheet.

  • 0 in reply to iAdrian
    TI__Genius 15975 points

    Hi Adrian,

    Something tells me that the SOIC package in a breadboard might not be transferring heat out of the chip. Is there a possibility that you could tell whether there is are PowerPAD holes or plane beneath the SOIC package?

    It might be that the thermal pads beneath the package are not transferring heat and that's why the chip is getting heated up.

    Rohit

  • 0 in reply to Rohit Bhat
    Prodigy 110 points

    Hey Rohit,

    There is no PowerPAD on this package.  The strange part is that I'm using this opamp for a filter and a buffer in different parts of my application.  When I use it as a filter (second-order unity-gain sallen-key) it works perfectly, but when I connect it as a buffer it starts to heat up.  I used the same chip in both cases (which is soldered to a small breakout board and placed on the breadboard).  I can't think of any reason why this would happen.

    -Adrian

  • 0 in reply to iAdrian
    Prodigy 110 points

    Also, I just noticed the problem only occurs when using the opamp with dual rail.  It doesn't output the correct voltage when connected with a dual rail supply.  If i use it with a single rail it works fine.

  • 0 in reply to iAdrian
    TI__Genius 15975 points

    Hi Adrian,

    Please make sure your supplies are connected correctly. For dual rail you should use a split supply connection. Usually it will be a +12V, -12V and COM port on the Power Supply depending upon which supply you are using.

    Also, could you please attach the schematic of the circuit that you are using. It would be easier for me to debug properly as well.

    Best Regards,

    Rohit

  • 0 in reply to iAdrian
    TI__Genius 13935 points

    In the SOIC package 15mA at 24V should induce a 34 degree C temperature rise. 

    I agree with Rohit that a schematic would help a lot.

    Also, a unity gain configuration with no load is not going to be stable on a breadboard.  The bread board parasitic capacitance will cause problems if not mitigated somehow. 

  • 0 in reply to Loren Siebert 1
    Prodigy 110 points

    Sorry, I did not attach a schematic because it is very simple: a unity gain buffer configuration, with the decoupling capacitors on the supplies.  Input voltage is within the ICMR and supply at +/-12V.  

    Regarding your comment on stability, I feared this might be happening because It wasn't functioning properly as a buffer.  How do you suggest I compensate for this?

  • 0 in reply to iAdrian
    TI__Genius 13935 points

    Hi Adrian,

    You can try to solder a capacitor in parallel with the feedback resistor, start with 10pF.  

    If you have room on the adapter try to put a series resistor between the IC output pin and the connection to the breadboard (but after the feedback resistor).  

    Loren

  • 0 in reply to Loren Siebert 1
    Prodigy 110 points

    Hey Loren,

    Soldered a 20pF capacitor as you suggested and it worked perfectly.  I'm using these to make a PGA and I noticed it was oscillating when I measured the output.  Thanks for the tip!

    Adrian