Hi everyone.
I have designed a 4x4 Audio Matrix with 4 x TPA3123D2 in the output stages.
I have a weird problem which I hope you can help me with.
As I said there are 4 of these amps on a board. (Call them channel 1 to 4). The MUTE and !SD signals are hooked up to a micro controller.
When the board powers up there is no pop at all from the speakers. The micro holds them in MUTE and SHUTDOWN during power up. In the following description, by shutdown I mean asserting !SD and by switching on/off I simply mean asserting/de-asserting the !SD signal. The VCC and PVCCL and PVCCR lines are always powered up.
When I turn the individual channels on (by de-asserting the shutdown signal) there is no pop when each channel turns on - except for channel 2 - which gives a kind of double-pop ("KUH-POP" type noise) as it comes out of shutdown, or goes into shutdown - but only the first couple of times. If you turn it on/off few times the POP each time goes away after about 2 cycles and then the whole thing is lovely and quiet in operation, with great audio quality on all channels. What could be the cause of the POPPING on this one amp during it's first couple of shutdown cycles?
While it is running nicely with no popping you can make channel 2 pop again by doing this:
Turn on channels 1 to 4. Then switch off channels 1, 3 and 4. Now switch off channel 2 and it will KUH-POP when it goes off and again when it comes on. The the whole thing will be nice an quiet again.
I have checked and replaced all the capacitors on VBYP and CLAMP - originally I had polarised electrolytics at 1uF - which I have now changed to tantalums - but it made no difference.
The PVCC and VCC lines are all common.
