• Resolved

TPA6141A2: 【Urgent】 RF noise filter of TPA6141A2's output

Expert 2970 points

Part Number: TPA6141A2

Dear Technical Support Team,

 

I'd like to confirm the RF noise filter of TPA6141A2's output urgently.

Our customer is launching mass production.

 

They are designing the Bluetooth speaker and it can connect an earphone cable with TPA6141A2.

When connecting an earphone cable to jack, approximately 150MHz RF noise affects TPA6141A2 through earphone cable.

To prevent this RF noise, 1000pF capacitors are set on OUTL and OUTR.

 

Could you see the attached file?

TPA6141A2.pptx

 

■Questions

1.) Do you have a solution to reduce RF noise through earphone cable?

2.) Is 1000pF OK to reduce RF noise? I'm concern an oscillation of headphone AMP.

    The datasheet doesn't show capacitive load specification.

3.) Is it better to set the sunber circuit(C and R) on OUTR and OUTL?

      if possible , could you show the value of C and R for sunber circuit. 

 

Best Regards,

ttd

  • Hi ttd,

    If you're concerned about capacitive loading you could use a series R = 220 and C = 270pF to GND. Regarding some possible snubber values maybe you could use R = 150 and C = 2.2nF.

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio and Actuators
  • Expert 2970 points

    In reply to Ivan Salazar:

    Hi Ivan,

    Thank you for your reply.
    I suggested the LPF(series R = 220 and C = 270pF) and snubber(R = 150 and C = 2.2nF) to our customer.
    Unfortunately, they had already fixed their board because of mass production.
    So their board doesn't place a resistor.

    They tried an immunity test and sweep AM modulation(1kHz / 80%) from a few hundred kHz to 3GHz with earphone.
    Then this problem causes around 150MHz.
    It seems that the RF noise reaches TPA6141A2 trough earphone(OUTR / OUTL).
    To reduce it, insert C = 1000pF to GND on OUTR and OUTL.

    ■Questions
    1.) Is it possible to use only C = 1000pF to GND on OUTR and OUTL ?
    2.) Have you tried immunity test with earphone like our customer ?

    Best Regards,
    ttd
  • In reply to ttd:

    Hi ttd,

    We haven't performed immunity test so unfortunately we don't have any results to share.
    It may be possible to use only the output capacitor to GND but I would recommend to test it to verify that it is safe from an oscillation perspective.

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio and Actuators
  • Expert 2970 points

    In reply to Ivan Salazar:

    Hi Ivan,

    Thank you for your reply.
    My customer is testing only the output capacitor to GND.

    By the way, do you have a figure of Open-Loop Gain and Phase vs Frequency?

    Best Regards,
    ttd
  • Expert 2970 points

    In reply to ttd:

    Hi Ivan,

    Do you have any update about Open-Loop Gain and Phase vs Frequency?
    If you have it or not, please let me know.
    Thank you for your cooperation.

    Best Regards,
    ttd
  • In reply to ttd:

    Hi ttd,

    Unfortunately this data is not available for this device. All the information available is in the data sheet and user´s guide.

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio & Actuators
  • In reply to Ivan Salazar:

    Hi Iavn-san,

    Since Head Phone amp needs to drive unknown long cable which include largecapacitance and inductance.
    During TPA6141A2 characterization test, how large capacitive load was applied to confirm stability?
    What is TI HP-amp design spec to keep stable operation in the market?

    Regards,
    Mochizuki
  • In reply to Kazuto Mochizuki:

    Hello Ivan-san,

    In the case of TPA4411 datasheet, we can find the specification as "Maximum capacitive load   400PF" .

    What about TPA614x family's capacitive load drivability specification?

    Regards,

    Mochizuki

  • In reply to Kazuto Mochizuki:

    Mochizuki-san,

    Capacitive load is not specified in TPA614x data sheet. Perhaps this was not documented during characterization.
    However I found an old report of stability on TPA6140A2 that could be helpfull. Please find attached document.

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio & Actuators

    5826.TPA6140_Stability_Matrix.xls

  • In reply to Ivan Salazar:

    Ivan-san,

     

    Thank you very much for your information,

    It will help to get some idea from my customer.

     

    Regards,

    Mochizuki