Output Crash when power down ADAU1446 pcb and power amp

HI Fabio:

Can you try to mute the signal flow (in SigmaStudio) before you start doing the processing and after all the processing is done. Doing so would clear all memory and prevent unwanted digital noise comming from the core, this may remove potential garbage data, a potential source of unwanted noise. There are other reasons why you might be getting digital noise but, how about tryin this to start?

Futhermore, you might want to start your shutdown sequenc by mutting the 1939, then the Amp and lastly the DSP.

Of course, as you mention telling the micro to shut down the amp before the DSP would probably solve the problem if this shutdown is noise free.

Let us know your results

Regards

Miguel

Hi Miguel,

I have tried out to mute the DSP before shutting down the whole system. The problem is still there. So it should be an AD1939 or an analog issue. For a brief moment during turn off the power supply, I can measure an undefined voltage at the analog output. Then, the voltage get a bit negative (about 10mV) and after that, the output stabilizes at 0V. I have attached the analog input and analog output stage as JPEG. Maybe you can find the reason for this crashing/cracking/... whatever...

A possibility I have, is to disable the amp with a GPIO of the DSP. But how can I know, when the DSP should start its shutdown sequence and how can I program this sequence? How can I detect, that the pcb lose its power?

Best regards,

Fabio

https://ez.analog.com/cfs-file/__key/communityserver-discussions-components-files/396/87e6856eb6757e96d0e3d38d26adb2f3.html

Sorry, I did not load up the schematics. So here they are...

Fabio

I had the same problem. You can try to send command to mute the DACs and ADCs, instead of muting the signal flow. This should be an improvement.

I had the same problem too, and I completely fixed it by letting the microcontroller immediately MUTE the amplifier as soon as it detects a drop in the power supply voltage, then, what happens at the DSP output doesn't matter.

If you have a regulator for your digital stuff, that shoud be easy, for example:

PSU -> V-Regulator -> uC and DSPs.

You put a resistor divider before the regulator and feed to the microcontroller. This way, as soon as the voltage drops a litte, the microcontroller will know before the regulator looses regulation. You should use an interrupt service routine on your microcontroller code to sense and service it immediately.

Muting the amplifier should be easy, most AMP chips have a mute pin. If it doesn't have one, you can always use a FET to mute the input.

Audio ---> FET (in series) ---> AMP.

Once the fet opens, the signal is interrupted. Add a resistor like 22k to the ground on the amp input so it doesn't float.

Good luck.

Thank you, Nando.One,

This is exactly what I have searched for, I think it should work. I wasn't at work the last 2 weeks, but I will try this immediately next week! Then I'm able to tell you the results.

Best regards,

grimbart

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