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TLV320AIC3254EVM-K without I2S data, analog microphones to headphones with PLL

Mark Pickles
Prodigy 20 points

I am attempting to configure 2 analog microphones (differential IN2 and IN3) and route the audio to the headphones, using the ADC and DAC. Due to system clock limitations I can only provide a 1MHz input clock. So I've configured the clocks with the PLL with a 16kHz sample rate. The clock is applied directly to pin 17 of P22/J22 and I've switched off SW 2.4 (USB I2S) and 2.5 (USB MCK).

No audio can be heard from the microphones. BUT if I switch on 2.4 (USB I2S) the microphone audio starts to be heard and now if I switch off 2.4 (USB I2S) the microphone audio continues to be heard. It seems that the short burst of I2S clock starts the audio. Looking at the status flags from the GUI, before the I2S clock is applied, the following flags are off - ADC Left/Right PGA gain = programmed gain, LDAC/RDAC PGA gain = programmed gain. After the I2S clock burst all these status flags go green, and remain gren even if the I2S clock is then switched off.

I've tried various tweaks, such as disabling the ADC/DAC soft stepping but without resolving the issue.

Is the I2S clock required (although briefly) even if the I2S bus is not being used? Or am I missing some other settings?

Thanks in advance,

Mark Pickles.

  • 0
    Prodigy 20 points

    My sort of solution.

    The I2S can be set as master or slave and is slave by default. If I change the BCLK and WCLK directions to outputs and power on the BDIV_CLKIN, then the microphones start working. But since we don't want these clocks as outputs and the extra power usage, if I add a 30ms delay, then reverse the changes, power down the BDIV_CLKIN and change the BCLK and WCLK directions to inputs, the microphones continue to work.