TPA3112D1: Power-up Issue

Hi,

It seems OC or DC fault happened.

1) You can disconnect audio input and check if the issue gone, if yes, the Isat of inductor is not enough. Please check inductor design.

2) Remove the output inductor and check if the issue gone. If yes, please check audio input DC caps(1uF), it maybe some issues on capacitors.

Regards,

Derek 

I'm still working to disconnect two of the amplifier inputs, but noticed the buffer amps take a long time to settle to their final output value.  It does cause the positive input to go above 3V.

The amplifier I can easily disconnect, seems to power up very reliably (the board with two amps on it).  I have not been able to short out the inductors yet, but I checked the parts I am using.  They have nearly the same Isat as the parts on the eval board and are from the same manufacturer.  Does a 100mA lower Isat rating cause this issue?

Eval board   B952AS-220M, series DS104C2, 2.4A        

My board     1264EY-220M, series DG6050C, 2.3A

Thank you.

Hi Scott,

Did you remove input DC caps(1uF) when disconnect audio input? Please do not remove the DC caps.

So you mean that you remove load(speaker), then the amplifiers work well, right?

What's the load impendence? What's the output power when issue happened? Did you monitor the output current when issue happened?

Regards,

Derek 

No, I did not remove the input capacitors.  I removed JP3 since we do not have stereo input yet.  There is no connection on J19,pin3.  U7 then has an input and U9 does not.  The speaker loads are disconnected at this point.  U7 powers up correctly 50% of the time, U9 seems to power up correctly every time with JP3 removed.  50% if JP3 is installed.

I tried holding the /SD pin low during power-up then releasing a few seconds later.  The amp then powers up every time.  I installed JP3 and held U7-pin1 low.  I did not hold U9-pin1 low.  U7 powered up every time.  U9 did not power up.  Speakers were disconnected.

Hi Scott,

According to your description, I think there has big noise input to amplifier TPA3112 when issue happened. When power up, there has big noise input, it leads to big power. The noise seems come from U4, U6 and U8. 

You can check the output current and output waveform when issue happened.

And you also can short or remove U4, U6 and U8 to double check again.

Regards

Derek

I shorted the bias resistor on the input of the buffer to prevent the large signal on power-up.  The amplifiers powered up properly.  When I removed the short after the amp was powered, the amp momentarily shutdown (fault), then auto restarted.  Was this the intended behavior for the auto restart (not to restart under some conditions)?

I believe we can increase the cutoff frequency of the HPF in front of the buffers which is currently about 1.6Hz.  How much do I need to increase the cutoff freq so that the auto restart circuit behaves properly?

We included the buffers since the input impedance of the amplifier varies with gain setting.  Does TI have a similar part that incorporates an input buffer or can some way maintain a higher input impedance over all gain settings?