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TPA0172 I2C issue - Not completing power up sequence

ryan trann
Prodigy 65 points 
Hello,

I'm trying to adjust the I2C registers on my TPA0172 amplifier, however when I read from the I2C 
bus, it appears to never complete the power up sequence. Bit 7 of register 5 (mask register)
never goes to 0.

I read this information from the bus.

READ
Register 1 3F
Register 2 3F
Register 3 3F
Register 4 3F
Register 5 FF
Register 6 0

Which is all correct for the power up values of this amplifier, but register 5 should change to 7F
when it's done powering up, according to my understanding from the data sheets. Then I 
should be able to write to it.

Any ideas? 

Currently running

2.2k pull up resistors on SDA, SCL
I2CVdd = 5v
The master device is an mbed uC and the TPA0172 is the only slave on the bus.

 Thanks for the help.

Ryan
  • 0
    Prodigy 65 points

    Can a TI employee please have a look at this.

    Thanks

    Ryan

  • 0 in reply to ryan trann
    TI__Guru**** 189399 points

    Hi, Ryan,

    Have you tried programming any of the registers and reading them back to see if they "took?"

    I think the power-up bit is for the audio path to be enabled, you should be able to write the I2C w/o that going high.

    Then try applying audio.

    That part is > 10 years old, so my memory is a little bit fuzzier than normal, but we probably have a comparator on the BYPASS pin that checks the voltage and/or current into the BYPASS cap that disables the audio path until the BYPASS cap is nearly fully charged for pop reasons. So, it might have a problem if your BYPASS cap (or PCB or whatever) has high leakage current, and the cap can't charge up. Take a look at the voltage on it, it should be VDD/2. If it's not, you need to figure out if there is leakage on your cap or board or ?

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 65 points

    Hey don,

    I think you're right about the leakage on the cap. I removed it while the amp was powering up to try some different caps and as soon as I did that the powerup sequence completed. I was getting it completing off and on earlier yesterday and that inconsistency seemed very strange. I'll swap it out for a proper cap like one suggested in the data sheet. 

    I suppose that would also account for why I could't pass audio through the amp. The few times it did complete powerup and I wrote to the gain register, It didn't seem to have an effect and I could't amplify a signal through the the device.

    I'm sure that I can write properly to the registers, when I switched between SE and BTL the resulting current jump showed that the write operation did work. Also when I read it again the values I wrote are read correctly.

    Thanks so much! I'll try some things and get back to you with results.

    Ryan

    P.S. I had no idea the device was so out of date could you perhaps suggest a something more current that I could use?

  • 0 in reply to ryan trann
    Prodigy 65 points

    I tried a .5 uF low esr tantalum cap in place of the bypass cap and it basically didn't change anything. I was reading about 100mV across it and the powerup sequence wouldnt complete. I also tried some other smaller capacitor values with no luck.

    At this point I have the power up sequence completing every time when there is no cap in place and the bypass pin is floating. However I still cannot get audio to pass through the circuit, I can receive my input sine wave (p17) at the output (p12) but it is attenuated and noisy (about 20mVpp from an input of 600mVpp).

    These are the values I'm writing to the registers.

    WRITE
    Register 1 0
    Register 2 0
    Register 3 0
    Register 4 0
    Register 5 0
    Register 6 72

    Thanks again in advance.

    Ryan

    EDIT* I just tried it again with the tantalum cap and it eventually started up with the correct 2.5v drop across, however still not passing audio through the cct. Perhaps the bypass cap isn't the issue with my amplification problem? I'm not using tantalum caps all across the circuit, is that a big issue?

  • 0 in reply to ryan trann
    TI__Guru**** 189399 points

    Ryan,

    That is very odd.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 65 points

    yea, my guess at this point is that it's somehow damaged. I suppose it's time to move onto another amplifier.