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PCM3168A - NE5532 HEATING PROBLEM

omeraygor
Intellectual 410 points
Other Parts Discussed in Thread: PCM3168A, NE5532

Hi, 

i have custom board with PCM3168A. in the datasheet of pcm3168a it offers to inputs as input buffer  at page 56. like this:

On my pcb, there are input buffers as picture.

But my problem is, NE5532 is heating even though PCM3168a not working.  everything is same as figure 59 design. 

thanks. 

 

  • 0
    TI__Mastermind 28020 points
    Hi Omeraygor,

    Have you tried looking at the input to this circuit to see is there is any oscillation that might be causing the NE5532's to heat up? What is the current draw of the NE parts? Have you checked that there are no accidental shorts on your board?

    Justin
  • 0 in reply to Justin Bohr
    Intellectual 410 points
    Hi justin,

    i think, the heating reason could be oscillation. but what causes i dont know.

    i checked the board and it has not any shorts. so i tried with another board without placed pcm3168a , so only the circuit is above.
    it is also heating.

    While the circuit is alone , the vcomad pin voltage is applied 0V.

    But in my circut, i forgat bypass capacitors to each opamp, you think is it cause the oscillation and heating?

    and the power supply to opamps +-12V dc (Switching power supply meanwell PD-2512) switch frequency 100khz.

    www.mouser.com/.../r330_3-4354.pdf
  • 0 in reply to omeraygor
    Intellectual 410 points

    Hi,

    i cant resolve my problem. is there any help?

    Thanks. 

  • 0 in reply to omeraygor
    TI__Mastermind 28020 points
    Hi Omeraygor,

    The missing bypass caps could be the reason the op amps are acting this way. With the op amps biased to VCOM, and the input at 0V then this would be pushing a full scale output by the op amps which could heat them up.

    What is the temperature that the NE5534s are heating up to, is it out of the limits in the data sheet? Do you have a way to measure the current draw of the NE parts?

    Justin
  • 0 in reply to Justin Bohr
    Intellectual 410 points

    Hi Justin,

    I add bypass caps manually. 

    inputs can be left blank. so it can be 0V. but while i dont connect to audio source to inputs, what can i do?

    it must be open sometimes when i dont use. is there anything i forgot input side of opamp.

    The temperature about 40 C. it is not increase. it is allways about this temp. 

    i did not measure current draw. i will today. 

  • 0 in reply to omeraygor
    TI__Mastermind 28020 points
    Hi Omeraygor,

    If the bypass caps are not in place and the op amp is biased to mid rail, then having a 0V input will be staining the op amps to output a voltage difference of the bias (VCOM) to 0 V. This could be heating up the op amps. What is the output of the opamps when there is no input?

    Justin