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PCM1681: DRV135

Part Number: PCM1681
Other Parts Discussed in Thread: DRV135, TPS563209

Hello,

We designed a product and it is out in market now, but we are seeing failure scenarios at where PCM1681 gets damaged.

We kept provisions for Phantom power on all XLR outputs which is connected to DRV135. Please see attached image for reference.

So we are concern that do we need to put special protection at input (VCC) of PCM1681 as +5VADD is used for powering PCM1681, DRV135 and XLR outputs.

Please advise. 

Thank you

-Aman Shah

  • Hello Aman,

    Typically for the PCM1681 we only recommend a 0.1uF bypass capacitor at the VCC pins. Can you give us any more information on the failure? Does this happen over time during use or is it something that happens during production/testing? 

    The PCM1681 should be fine as long as the absolute maximum ratings from the datasheet are not exceeded. Have you detected any large transients on the +5AVDD rail, perhaps when plugging and unplugging the XLR? If so, a scope capture of that transient may be helpful in recommending a possible fix.

    Best Regards,

    Brandon Fisher

  • Hello Brandon,

    Thank you for your response.

    We found that it is working fine in normal environment (during testing and normal use with/ without Phantom Power).

    But, Our customer came back with the issue that when they connect the XLR connector with phantom power turned ON (when the unit is already powered ON), the device stops functioning . After troubleshooting we found PCM1681 damaged (couldn't see any external burn mark or damages) and replacing the part resolve the issue. We haven't seen this issue in every unit. Up till now we have seen this issue in approximately 5 out of 500 units and most of the time units were connected to High end Sound mixers (For Example, DIGICO SD8).

    We can provide you the scope on +5AVDD with the unit we have.

    Please review and provide your feedback.

    Thank you.

    Best Regards,
    -Aman Shah
  • Hi  Aman,

    Can you clarify why an XLR with phantom power is being connected to a DAC Output XLR? I would expect that there would be a male/female mismatch on these connections.

    Typically phantom power connections are current limited. If this is not the case for the device you are connecting to, then the +5AVDD is probably getting pulled high, which could possibly damage the device.

    If you can take and upload a scope capture of the power rails when connecting that will let us know if that is what is happening. 

    Best Regards,
    Brandon Fisher

  • Hello Brandon,

    Sorry, we are not able to understand DAC Output XLR connection. You mean to say that why VCC (which is connected to +5AVDD) of PCM1681 is connected to XLR connector? We made this arrangement to protect DRV135 from Phantom Power.

    Also, We can upload a scope of power rails when connecting XLR on the unit what we have it. But we do not have that particular equipment which is failing/ damaging PCM1681 in unit.

    Thank you.

    Best Regards,
    Aman Shah
  • Aman,

    Do you see any unusual activity on the +5AVDD rail of the working units when you connect the XLR connector with phantom power turned on? If so that would be useful to see.

    Even if most of the PCM1681s survive, I would expect that all of the boards would show some amount of the issue if the +5AVDD rail spiking is the cause.

    Best Regards,
    Brandon Fisher
  • Hello Brandon,

    Yes, we found couple of spikes come when we plug XLR connector with Phantom power. Please see attached scope results which is taken on +5VADD rail. Also, we find that we were not able to see spike every time when we plug the XLR.

    Please review and advise.

    Thank you.

    Best Regards,

    Aman Shah

  • Hello Aman,

    Thanks for sharing the image. It looks like the transient on that rail is well above the 6V absolute maximum we recommend for the PCM1681, even with the additional capacitance you have on the line. It's likely that most of the PCM1681s are surviving because the internal ESD structure is managing to protect them, but some of them will always fail under that level of stress.

    If possible, I would recommend using a TVS diode to clamp +5AVDD below 6V. This will consume additional current during the transient, but since this is only happening during connection of the XLR with Phantom Power on, I don't believe it will noticeably affect your current draw.

    There are likely other options to fix this elsewhere in your power stage, but I think adding a TVS diode would be the simplest solution.

    Best Regards,
    Brandon Fisher
  • Hello Brandon,

    Thank you for your response. We will try your suggestion and provide you feedback.

    Best Regards,
    Aman Shah
  • Hello Brandon,

    We took your suggestion and put an zener diode (Part# ZEN056V075A48LS) on Vcc.

    With this fix we are getting maximum 7.8V spike on PCM1681 VCC. Please see the attached scope image of Vin of Zener.

    And on Vout we are getting 7.84V peak which goes into PCM1681 Vcc.

    Would this be a good solution to protect PCM1681 from high voltage spikes? Or do we need to suppress this voltage more and bring it below 6V.

    Also, we have PESD5V0H1BSFYL (5V TVS Diode). So is it better option to use that diode? If so then how would you suggest to make connections as this one is bi-directional.

    Please advise on that, too.

    Thank you.

    Best Regards,

    Aman Shah

  • Hello Brandon,

    We took your suggestion and put an zener diode (Part# ZEN056V075A48LS) on Vcc.

    With this fix we are getting maximum 7.8V spike on PCM1681 VCC. Please see the attached scope image of Vin of Zener.

    And on Vout we are getting 7.84V peak which goes into PCM1681 Vcc.

    Would this be a good solution to protect PCM1681 from high voltage spikes? Or do we need to suppress this voltage more and bring it below 6V.

    Also, we have PESD5V0H1BSFYL (5V TVS Diode). So is it better option to use that diode? If so then how would you suggest to make connections as this one is bi-directional.

    Please advise on that, too.

    Thank you.

    Best Regards,

    Aman Shah

  • Hi Aman,

    The reduction of the spike to 7.8 V will decrease the number of devices that you have failing, but I can't guarantee that it would totally eliminate the failures given that 7.8V is still above our recommended max of 6V.

    You should make sure that your diode is placed as close as possible to the device. I'd recommend trying the 5V TVS diode which you can connect as shown in the image below from the diode datasheet. In this case the line to be protected is +5AVDD as close as possible to the PCM1681.

    Keep in mind that using a TVS diode with a standoff voltage of 5V will mean that you will have some constant current being conducted from +5AVDD to ground through this diode at essentially all times. The diode datasheet suggests that 50nA is the max you will see here, but that is only true if your rail is exactly at the standoff voltage. 

    Best Regards,
    Brandon Fisher

  • Hello Brandon,

    We tried above suggestion along with few other options. But we are still seeing high voltage spikes on PCM1681 Vcc pin.
    This is happening only when we plugged the XLR cable with phantom power ON and unit is sending the audio signal on XLR port.

    Please advice any alternatives to resolve this issue.

    Thank you,
    Aman Shah
  • Hi Aman,

    To clarify, you say this is happening when the XLR Cable with phantom power is plugged in and the unit is sending audio. Does this still happen if the unit is not sending Audio? 

    Other than that, there are a few more things you can check. Are you seeing this voltage spike on the +5V Rail (on the left side of L3 in your schematic)? How are you generating that rail? Is it sourced from the Phantom Power connection in any way? 

    Best Regards,
    Brandon Fisher

  • Hello Brandon,

    To clarify, you say this is happening when the XLR Cable with phantom power is plugged in and the unit is sending audio. Does this still happen if the unit is not sending Audio?

    --> Yes, it is happening in both the cases.

    Other than that, there are a few more things you can check. Are you seeing this voltage spike on the +5V Rail (on the left side of L3 in your schematic)? How are you generating that rail? Is it sourced from the Phantom Power connection in any way?

    --> Yes, we can see spike on the other side of +5V Rail. Also, we are converting +5V from +12V input of the board. Please see below schematic.

    Thank you.

    Best Regards,

    Aman Shah

  • Hi Aman,

    If you want to fix this on the +5V rail side, you can attempt to limit the inrush current using a resistor, or more preferably a series NTC leading to the supply of the PCM1681, they make NTCs specifically for inrush current limiting. The problem here is of course that there will be some voltage drop across that resistor at steady state, as well as some thermal noise on the supply from it. If that does not help minimize the transient enough then you may have to try a combination of that and the TVS diode solution from before.

    Before you do that though, I would take a measurement of the total current draw from the +5V rail in order to determine the magnitude of current flowing. I suspect that if you measured the +12V rail you would see a larger spike was present when you plugged in the phantom power connector. If that's true, the spike on the +5V rail is probably consistent with the transient response of the TPS563209.

    Best Regards,
    Brandon Fisher
  • Hi Aman,

    Do you have any updates for us on this topic?
  • Hello Kevin,

    While observing the voltages we found that we were taking wrong reference ground.

    We will implement the TVS diode and observe the voltage spike again.

    I will update you on this tomorrow on this.

    Regards,
    Aman Shah
  • Aman,

    Do you have results from the new setup?
  • Hello Kevin,

    Sorry for delay.

    We modified our exciting board and isolate +5VADD line from XLR output whgich was connected to same diode (at DRV135 for phantom power protection) and PCM1681 VCC through a plane.

    We placed a zener diode (zen056v075a48ls) between +5VADD of Diodes (at DRV135 for phantom power protection) and output of U12.
    We observed with above changes that the voltage spikes is reduced significant and now we see max spike of 6.2 to 6.4V.

    Also, we sent this unit to our customer for more detail testing as we do not have same setup here for which the board is failing in the field. Once we have any inputs on that we will update you in regard to close this case or need more help.

    Thank you.

    Best Regards,
    Aman Shah
  • Hi Aman,

    For now I will mark this thread as closed then. In 2 weeks it will automatically lock if you do not have any follow up. However, you may click "ask a related question" or create a new thread and myself or someone on my team will continue to follow up with you.