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PCM 3001 does DA conversion but not AD conversion

dwarf vader
Prodigy 40 points
Other Parts Discussed in Thread: PCM3001

I am using a PCM 3001 CODEC and have a little problem with it...

i can generate a wave on the output , but the AD conversion is not working at all , i do not see any digital data on the DOUT line.

does anybody have an idea what could be the reason for that ?

 

 

 

 

  • 0
    TI__Guru**** 189399 points

    Hi, Dwarf,

    Did you follow figure 34 of the d/s? Did you read the sections of the d/s immediately following figure 34?

    What voltage do you measure on pins 4 and 5?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 40 points

    I checked my circuit and its the same as the one in the data sheet.

    I measured  2.3 V   on pin4/5 to gnd and   0 V  between pin 4 and 5.

     

    i also read the instructions after fig. 34 and followed those.

     

    As you can see i am also controlling the reset and the power on to the PCM 3001 from the MCU.

     

    what i do is..

    1 . on startup the MCU pulls the RST up and waits 2 seconds.

    2. now it supplies the MCKL to the codec

    3 .  then it turns the power to the VCC1 ,VCC2 and VDD on so the codec can initialize  and waits 5 seconds

    3 .  then it performs an external reset procedure

    4 . now it activates the SSC and supplies the codec with DOUT / BCKL / FSYNC / MCKL.

     

     

    Still i have the problem of no DOUT but analog signal is generated successfully. 

    sometimes when i reset i see some junk data being emited from DOUT but nothing during the regular operation.

     

  • 0 in reply to dwarf vader
    Prodigy 40 points

    I think i found the solution.

     

    it was not an electrical issue it was a timing issue which is not mentioned in the data sheet and if it is not clearly.

    Assuming that one uses a 24.5 MHz master clock to drive the codec  and  32Bit DSP frame for the audio data the image above shows how to calculate the right bit clock frequency.

     

    This is something realy missing in the data sheet , the relation between MCKL and BCKIN.

     

    If anybody from TI sees this please add that to the next revision of the data sheet of the PCM3001 and probably to the data sheets of other codecs aswell that work similar.