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Pop/Click on power off of a TPA2006D1 .

Matthew Byrd
Prodigy 75 points
Other Parts Discussed in Thread: TPA2006D1

We make Active noise reduction modules for headsets. I recently replaced our old BTL chip with your class D. Everything is fine except for a violent click on power off. The circuit is comprised of a mic preamp into a lead/lag filter that is buffered on output through a unity gain opamp. The filter and preamp are referenced mid-supply. When I had the IN- of the class D tied to battery ground (with a capacitor) there was a loud pop coming on but when I tied it to the vref this mitigated the on going click. So it is single ended input to differential output and I have payed attention to matching impedances on the IN+ and IN- of the TPA2006D1. I did have a RC delay setup on the SD pin and it worked well coming on but going off the class D did not like it so I removed it but the click did not go away....... I'm at a loss! Oh yes and the impedance of the speaker is 42 ohms and the gain is set low on the class D and high at the filter (I had it the other way but saw that you did not recommend that) I spent a day and a half reading and scanning the forum (over 1250 posts) looking for a clue but did not find it...hence the post.

Regards,

Matthew Byrd

Headsets Inc.

  • 0
    TI__Guru**** 189399 points

    Hi, Matthew,

    Thanks for taking time to search the forum for an answer before posting!

    I'm a little confused. You say power off and pulling /Shutdown low. Are you actually removing the power supply to our IC, or does the pop happen when you maintain the power supply and simply cycle the /Shutdown pin?

    It's been a while since I worked on that part, so I don't 100% remember, but I think /Shutdown should be pretty quiet going into and coming out of shutdown if everything else is correct. Are you sure the previous stage isn't generating a transient that is being fed to our amp before it completes the /Shutdown sequence? Do you have scope shots of the pop?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 75 points

    Hello Dan,

          I started out using an RC delay for the sd pin so as to facilitate a soft-start. I did this by forming a voltage divider at the pin with a 400Kohm resistor in series with the internal 300Kohm resistor then at this node (sd pin) connected a 3.9uF MLCC to ground. It worked fine when turning on but when turning off the capacitor would discharge back through the internal 300K resistor and the class D would stutter or otherwise not exit cleanly. We are switching the power on/off. This circuit is entirely analog except for the class D. The soft-start network is currently removed.

    This is a capture of IN+ and IN-  through a power cycle.

    Top IN+ Bottom IN-  Middle A-B

    This is a capture at the diff out on power down.

    It sounds , smells  and feels like a biasing problem but I haven't fixed it yet!

    Regards,

    Matthew.

  • 0 in reply to Matthew Byrd
    TI__Guru**** 189399 points

    Hey, Matthew,

    The /SD pin is a digital logic pin. You can't do fancy footwork on it to slowly start the amp. Once you cross the threshold, it's going to start up/down.

    It looks like you've got an impedance mismatch on the two inputs which are causing a differential signal to be applied to the amp at start-up.

    However, I can't explain the little pulses on the outputs at power down...

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 75 points

    Thanks Don,

    Problem is solved using a brown out reset connected to sd pin (DS1813-5). Amplifier is very well behaved now.

    Regards,

    Matthew Byrd

    Headsets Inc.

    Amarillo Texas.

  • 0 in reply to Matthew Byrd
    TI__Guru**** 189399 points

    Hey, Matthew,

    Glad you got it working. I'm surprised a Maxim part actually works! :)

    We have plenty of SVSs at TI!!!

    -d2