• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 30 subscribers
  • Views 1189 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPA3112D1 entering thermal runaway

Pranit Upadrashta
Prodigy 40 points

Hello,

We have a few Class D ICs running on an audio board with an 18V supply rail being used to drive 8ohm speakers on a bus. Occasionally, the techs out in the field who install the devices might wire the speakers incorrectly and cause a short in the output or supply pins. 

According to the datasheet, the ICs should be protected because the output transistors enter a high impedance state. Even if that fails, the device should be protected from thermal runaway by thermal protection.

We have found that the ICs are still blowing up despite the error being improper wiring of the outputs. Any reason as to why this would happen? What other wiring mistakes could cause this problem on the TPA3112D1s?
Should we be adding additional circuit protections? 

We're using LTC3891EFE#PBF power supplies. It is unlikely that the slew rate on these is greater than 10V/ms so we haven't placed a 100k resistor in series with the gain pins.

Please let me know.

Thanks,

Pranit

  • 0
    TI__Guru**** 189399 points
    Hi, Pranit,

    Welcome to e2e, and thanks for your interest in our devices!

    Sorry to hear of your troubles. Normally, this device is quite robust with respect to shorts on the output pins. Have you studied exactly what combination causes the device to be damaged?

    This device is made from MOSFETs, so thermal runaway is highly unlikely. That is much more common with devices made using BJTs.

    Without knowing anything else, I would suggest the layout might be the cause of your troubles. Compare your layout to the EVM layout. Pay particular attention to the decoupling on the power supply terminals. This loop needs to be very small and tight as this is a high-performance switching amplifier.

    -d2
  • 0 in reply to Don Dapkus
    Prodigy 40 points

    Hi Don,

    Thank you for the reply, please look at the attached image and let me know if the power supply decoupling is alright. The loops themselves are very close to the IC (one cm max) 
    I don't know if my concern is relevant but I don't see a large decoupling capacitor for the lower frequencies on pins 15,16. Can this cause a problem?

    Thank you so much,

    Pranit

  • 0 in reply to Pranit Upadrashta
    TI__Guru**** 189399 points
    Hi, Pranit, C159 provides bulk decoupling for both channels. Bulk decoupling has much more series inductance, so the placement is not nearly as important as the local ceramic decoupling caps that you have highlighted. Those a CRITICAL to our amp's success!

    -d2