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THS4032CDGN Overcurrent Fault on PCB

Stephen Schaefer
Prodigy 20 points
Other Parts Discussed in Thread: THS4032

Hello all,

I'm experiencing some rather unusual fault behavior with the THS4032CDGN op-amp. My design uses op-amp in a split-supply application, with dual LM2596-ADJ buck regulators converting 24V input to a +-15V supply. The circuit is assembled using SMDs on a PCB. The power supply operates properly with no other components installed, drawing about 70 mA @ 24V quiescent current.

When I install the op-amp U1 (see the schematic below), with no other components installed, my 24V power supply collapses to about 2V @ 2.2A. The negative buck regulator outputs -3V, while the positive regulator outputs -200mV. The negative regulator becomes hot to the touch; other ICs do not. The op-amp outputs and inverting inputs show DC voltages ranging from -0.5V to -2V.

Next I removed U1 and installed U2, again with no other components installed. The circuit pulls between 100-110mA @ 24V, meaning U2 is responsible for about 30-40mA current draw. The +-15V supply operates normally. U2 quickly becomes hot to the touch. U2A outputs -12.8V (sticks to negative rail), while U2B outputs zero volts.

I repeated this procedure on another PCB and got the same (unwanted) results. The PCB is not faulted; I probed all the tracks and found no short-circuits. Can anybody offer some insight into this peculiar behavior? It's very difficult to solder the thermal pad underneath the DGN package. Am I perhaps frying the op-amps during hand-soldering?

  • 0
    Prodigy 20 points

    Check that, should read U6 and U7, not U1 and U2.

  • 0 in reply to Stephen Schaefer
    TI__Genius 15975 points

    Hi Stephen,

    It seems to me that when you solder down U6, something seems to be shorted in the PCB due to which the supply voltage is inappropriate. Can you also tell whether the chip becomes hot when U6 is placed? Also, do you have electrolytic capacitors on the PCB? Sometimes when the electrolytic capacitors are connected in the reverse polarity, it might drive sufficient current, which we have experienced in the past.

    You are cascading two stages of the THS4032 in the same chip and then connecting the output to the second cascade in the same chip. Can you make sure that the power supply to the part when THS4032 not in U6 comes out to be +/-15V from the regulators?

    Also, is there a specific reason as to why you have connected the +15V power supply in the signal path after U6?

    Best Regards,

    Rohit