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Original question:

TLV320DAC3100: SPK no Output

TLV320DAC3100: HPL short circuit error with SPK no output

Yuxi Liu(Tony)
Expert 3340 points
Part Number: TLV320DAC3100
Other Parts Discussed in Thread: LM4670

Hi TIer

I think I meet a same problem with e2e link:

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/841066/tlv320dac3100-spk-no-output?tisearch=e2e-sitesearch&keymatch=TLV320DAC3100%25252525252520short#

When I try to go to the maximum volume, I find that there is no output on the chip's speaker output. I checked the registers and found that the HPL shows the short circuit protection status. I removed the capacitor from the LC filter as in the previous E2E link and the circuit resumed. So I'm thinking about the root cause of the LC  L = 33uH  C = 10uF filter design error?

1. Also, for some reason, customers have added a first stage D class amplifier LM4670 in between the LC filter and the 9 ohm horn and set it to a gain of 1 .

2. Does this cause the TLV320 load impedance to become large and may increase the oscillation of the LC, which causes short-circuit protection? 

3. I captured the waveform on the positive and negative output of the speaker to ground when the short circuit protection occurs. It doesn't look like overshoot is happening .

4. The audio signal of the sound is around 650 Hz and I checked the LC capacitor PN: MSASG32NSB5106MTN.

Could you help me determine the root cause, thank you.

  • 0
    TI__Guru** 110615 points

    Hi Tony,

    It seems the LC filter may be oscillating due to the high-impedance input of the LM4670 amplifier's input. Filters are usually designed based on load R to determine the Q factor.
    I would suggest testing by driving the speaker directly from DAC3100, rather than using LM4670 in-between. Would that result in enough power?
    Another thing to check is if using RC filter instead of LC works better in this case.
    If they used LM4670 just for higher current drive capabilities, they may just use HPL/HPR from DAC3100 rather than the Class-D outputs. Internal signal routing should allow to drive the stereo headphone outputs as a differential pair.

    Best regards,
    -Ivan Salazar
    Applications Engineer