ADAU1761 with ground-centered headphone configuration

Hello,

we are using the ADAU1761 with headphone and speaker on outputs.

The speaker is connected via SSM2377 amplifier to the LOUTN/LOUTP pins, which are set as line out.

The headphone is connected as ground-centered to RHP/LHP pins using decopling capacitors.

We have got a problem of pops during AVDD switching on or off.

We have seen, that the outputs of HP and speaker are biased with AVDD/2 after switching on the AVDD power supply.

Is there any possibility to suppress the pops independently of applying the AVDD supply voltage?

Maybe there is a possibility to disable the AVDD/2 bias to analog outputs, or other cirquit popless solutions.

Please, give us some advices.

Thanks very much.

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  • 0
    •  Analog Employees 
    on Oct 9, 2014 6:06 PM

    Hello Andreas,

    There is a power-up pre-charge circuit to charge the capacitors on the output pins for suppressing the pop you are describing. Increasing the capacitor value on the CM pin will help slow down the charging and avoid the pop. The datasheet also mentions that the RC time constant of the load will also determine the charge time. I would see if you can slow this down by adjusting these values. This is discussed on page 37 of the datasheet.

    Then there is the shutdown pin (/SD) pin on the SSM2377 that can be used to keep the amplifier off for a short time during power up.

    There may be some other issues or suggestions to make. Can you post the output portion of your schematic showing the headphone outputs and the SSM2377 input implementation?

    Thanks,

    Dave T

Reply
  • 0
    •  Analog Employees 
    on Oct 9, 2014 6:06 PM

    Hello Andreas,

    There is a power-up pre-charge circuit to charge the capacitors on the output pins for suppressing the pop you are describing. Increasing the capacitor value on the CM pin will help slow down the charging and avoid the pop. The datasheet also mentions that the RC time constant of the load will also determine the charge time. I would see if you can slow this down by adjusting these values. This is discussed on page 37 of the datasheet.

    Then there is the shutdown pin (/SD) pin on the SSM2377 that can be used to keep the amplifier off for a short time during power up.

    There may be some other issues or suggestions to make. Can you post the output portion of your schematic showing the headphone outputs and the SSM2377 input implementation?

    Thanks,

    Dave T

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