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TDA4VH-Q1: Crystal doesn't start

Kefan Hu1
Prodigy 30 points
Part Number: TDA4VH-Q1
Other Parts Discussed in Thread: TDA4VH

Tool/software:

Hi.

We have been produced a few boards with TDA4VH. Among them, one board crystal doesn't work at all. I measured all power rails they seem to be good. PMIC also releases reset for both MCU and SOC. Initially I thought it's crystal tuning, but we measured other working board startup performance they are pretty good. Also, changing load capacitor doesn't change any startup behavior. Currently I suspect it could be some TDA4 internal fault. Please help to take a look and suggest next step.

Below is more information:

1. For the working board crystal start, measure on WKUP_OSC0_XI/XO

2. For the none working board (longer time vs ZOOMed) check the yellow trace.

 

First you may notice VPP is extremely low with DC offset dropped. In the zoomed picture, it's not even sinusoidal wave. To me it could be the amplifier issue.

I double checked VDDA_WKUP is powered up correctly. Do you have any insights? What's the other condition that could be preventing oscillator amplifier working properly?

Thanks,

Kevin

  • 0
    TI__Mastermind 20080 points

    Kevin,

    I am puzzled by this waveform too. You have obviously done the smart things to debug the problem. I think that the circuit could also look like it has an amplifier gain problem if there was a current path parallel to the crystal since this parallel path would reduce the effective amplifier gain.

    Could you make sure that you do not provide an intentional parallel resistance? (I assume that there is NO intentional resistance since the reference oscillator waveform looks good.)

    Could you either (a) re-solder the existing crystal or (b) try a different crystal? (I think a solder thread could produce an unintentional parallel current path.)

    Kevin

  • 0
    Prodigy 30 points

    All crystal related trial has been done including resoldering/replacing, changing capacitor etc. The layout is also straight forward on the top layer where no shortage is possible. Most interesting, the impedance testing during power off is closely same as the working board... My key question will be: should oscillator be working only with VDDA_WKUP powered up? Is there any other conditions?

    Kevin

  • 0 in reply to Kefan Hu1
    TI__Mastermind 20080 points

    The crystal oscillator is supposed to start based upon power VDDA_WKUP. I'd like you to give it VDD_MCU as well.

    I think the VDD_MCU is required for the path into the device, but the crystal oscillator use both supplies.

    Kevin