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PCM5100A: Schematics Review required for Audio DAC & Audio Amplifier with Potentiometer Volume Control

Sathiya Seelan Sekar1
Prodigy 160 points
Part Number: PCM5100A

Hi,

I am designing a board which drives the 2 Watt, 8 Ohm speaker (Part No: CMS-28528N-L152) in mono mode. External volume control knob is required to adjust the speaker volume output.

So, given provision to connect potentiometer.

Using the TI Audio DAC (Part No: PCM5100APWR) to drive the Audio Amplifier (Part No: LM4991MAX/NOPB). Output of DAC is controlled by external potentiometer (Pot Spec 100Kohm,0.25W, Part No: PDA241-SRT02-104A2 ).

Potentiometer Taper output is fed to the Audio Amplifier & output of Amplifier drives the speaker.

I have attached the Schematics of the design. Could anyone please review it & let me know if the circuit is correct.

Appreciate the quick response.

Thanks in advance.Audio DAC & Amplifier Circuit.pdf

Regards,

Sathiya

  • 0
    TI__Guru 53633 points

    Hi Sathiya,

    1. I would not directly short the DAC outputs together.  You could duplicate the 470Ω for each output.  This will help reduce current consumption as well. 

    2. The output of the DAC is 6Vpp, so if it is not attenuated you will rail the amplifier.  I suggest you increase the amplifier's supply and add some attenuation by changing the gain of the amp or adding a resistor divider on the DAC output before the pot.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 160 points

    Hi Paul,

    Thank you for the response. But my query is not resolved. I still have some doubt that need your help.

    Related to your response 1, the option is given such that either one of the resistor will be mounted at any time. By default, Left channel output is chosen & it is given 0 Ohm resistor in the path. Alternatively, No Stuff(NS) resistor option is given to use right channel output if we need to test.

    Related to response 2, I could see from the PCM5100A datasheet that the DAC Channel Line out voltage is 2.1Vrms (Full scale) in page 4. I do not understand 6Vpp out from DAC. Please help me to get clarity.

    Also, please note that my main intention behind raising this thread was to select how much resistance range for the externally controlled Potentiometer. I do not get any calculation formula to understand how much the attenuation the external Potentiometer will provide to the Audio Amplifier input.

    Please let me know is there any way I can simulate the output of this DAC output to Speaker Input chain?

    Please provide your review comments.

    Thank you in advance.

    Regards,

    Sathiya Seelan S

  • 0 in reply to Sathiya Seelan Sekar1
    TI__Guru 53633 points

    1. I understand - I originally thought you were trying to gang up the two channels or something.  Leaving one of the resistors non-populated is good.

    2. An output of 2.1VRMS is about 3Vpeak or 6Vpeak-peak at the fullscale output.  The PCM5100A features a charge pump to generate a negative supply of about -3.3V.  The output is centered at ground.

    It may be difficult for you to achieve 2W output with this circuit, as you see that you might be limited by the supply of the amplifier.

    For the attenuation of the circuit, let's say you want to use an input voltage of 1Vrms.  You will need to attenuate the DAC output by about 50%. You could use something like 10kΩ in series with the output connected to a 10kΩ potentiometer.  Ideally, a lower resistance divider is best , but less than 1kΩ total violates the output drive impedance specification of the PCM5100A.

    Thanks,

    Paul