PCM6340-Q1: MIC input problem

I measured 38TP29  just now, and it is still no waveform，may be there is a problem with VCC_MIC?

Hi Hui,

Is VCC mic supply sourced externally or provided from PCM6340 Micbias?

Either way, PCM6340 does not internally bias the input to the common mode voltage of the ADC so DC must be added externally (through TI device MICBIAS or External power). 

Ensure that the input is biased correctly for the output impedance of the microphone used. For a single-ended ECM microphone, typically the full input impedance is reference to MICBIAS. If differential, half the impedance, R/2 , is referenced to MICBIAS and R/2 is reference to GND.

Let me know if you have any additional questions

hi Daveon,

VCC mic is provided from PCM6340 Micbias, and I measured and 38tp04, there is no voltage output from pcm6340 after i write register by test_mic.sh, please help me to debug it, thanks.

Hi,

Ensure HVDD is supplied as MICBIAS can only be programmed 600mV less than the supply voltage. MICBIAS voltage is also set in register 0x3b, please measure test point again

hi，Daveon

HVDD is almost 7.5V, and  register 0x3b is set to 0x70, now i found that TP0004 and VCC_MIC_1 is almost 5V, and  38TP19(MIC1_GND) and 38TP20(MIC1_IN) also have voltages like below:

the register set is:

now I measured that 38TP08, found that no waveform output. please help me to debug it, thanks.

The register value of 0x76 and 0x77 is as follows, the register indicates that the ADC channel is powered down.

Hi Hui,

Can you provide full schematic offline to better debug MICBIAS supply. I've reached out to your email

Hi Hui,

What changes in schematic were made to resolve MICBIAS issue?

I don't know the reason why pcm6340 is working normally now，actually, i didn't make changes. and the value of register 0x76 and 0x77 is still 0x0 and 0xcc.