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Output Crash when power down ADAU1446 pcb and power amp

Question asked by grimbart on Aug 19, 2014
Latest reply on Sep 5, 2014 by grimbart



I have a question about power down my pcb (ADAU1446 and AD1939) in combination with a power amplifier and a loudspeaker. It crashes/crackles very very loud every time I turn off the power of the whole system!


I have the following structure on my pcb:

- analog input as on the ADAU1446 Evaluation board (except the OPamps has dual supply)

- digital conversion with AD1939 (at 96kHz, programmed over SPI with a PIC uC)

- signal processing with ADAU1446 (at 96kHz)

- analog conversion with AD1939 (...)

- analog output stage as recommended in the AD1939 Datasheet (except, there is a 10uF capacitor in the signal path directly before the output)


The power amplifier turns off at about 3 seconds after I turn off the power supply; the digital parts turn off earlier and cause the crashes/crackles/...!


1) Can I provide some simple changes in my analog design to avoid this problem?

2) Should I try to maintain the power supply of the pcb (e.g. with a goldCap or superCap)? (The power amplifier turns off very silently)


Best Regards,

Fabio P