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PGA2505: PGA2505 schematic review

Eddie Chou
Expert 5160 points
Part Number: PGA2505
Other Parts Discussed in Thread: LM4864, LM4990, LM3914, PGA2500

Hi Team,

would you help review our customer schematic and several questions below?

1. Input is from MIC XLR differential signal , and PGA2505 output is single ended output to Audio codec. how to connect PGA2505 with single ended output?

2. Can we connect LM4864 output 1 to headphone jack and output 2 to Codec?

Does LM4864 need DC block?

3. Headphone output need 0.5W RMS at 4Ω, if customer need connect single ended output, should they change to LM4990 ?

Thanks and Regards

EddieSCHEMATIC1 _ 03. Audio circuit.pdf

  • 0
    TI__Guru 51266 points
    Hi Eddie,

    On Question (1), it is possible to connect a single-ended Codec to one output of the PGA2500. If the input of the Audio Codec is DC coupled, the user will need to bias the VcomIN to half-scale of the Audio Codec input. Also, please note that the SIG input of LM3914 expects the input signal to be unipolar (shifted above ground, 0-5V), and therefore will need to connect the PGA2500 VcomIN to +2.5V to level shift the signal. The allowed range for the PGA2505 VcomIN pin is 0V to +2.5V.

    On question (2), I believe the LM4864 is a power amplifier intended to drive a single channel. In the schematic, it appears the user is attempting to drive a -L, -R stereo headphone jack with the LM4864? Please note that Vo1 and Vo2 outputs are intended to drive a single channel, since the Vo1 and Vo2 output signals are 180 degrees out of phase.

    The LM4864 device is supported by the Low Power Audio Group. I will move the E2E thread to the proper forum to address the LM4864 queries.

    Thanks and Regards,

    Luis
  • 0 in reply to Luis Chioye
    TI__Guru* 84915 points

    Hi, Eddie,

    Regarding your questions #2 and #3 related to the LM devices, please take a look at my responses below and let me know if you have additional questions or comments.

    2.- Can we connect LM4864 output 1 to headphone jack and output 2 to Codec?

    Does LM4864 need DC block?

    Yes, it is possible to split the LM4864 outputs in two different single-ended outputs. Just remember that the output 2 will be an inverted output 1 signal with an unity gain. So, all the changes on the output 1 gain will affect the output 2 result.

    You would only require to add DC-blocking capacitors between the LM4864 outputs and the codec/jack as shown in the schematic that you attached.

    3.- Headphone output need 0.5W RMS at 4Ω, if customer need connect single ended output, should they change to LM4990 ?

    Right. The LM4864 doesn't have enough current capabilities to handle a 4ohms load at 0.5W (with a VDD = 5.5V, it only can reach around 0.38W). So, the LM4990 can be used to reach this power with a 4ohms load.

    Best regards,
    Luis Fernando Rodríguez S.