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PCM9211: A partial circuit review request

MJ Jeon
Genius 5240 points
Part Number: PCM9211

Hi, TI support team

A partial circuit review request has been received from the customer.

Reference caps connected to pins 44 and 46. The value is 10uF and is written in the datasheet, but to improve the sound quality, we are going to change it from the existing value to 100uF and apply it.

If I change the capacitance as above, can there be any problem?

Thanks.

Regards,

MJ

  • 0
    Genius 5240 points

    Hi, TI support team

    I have additional inquiry.

    A general Electric Capacitor ( 16V / 100uF ) is used for the VCCAD port, but a Polymer Alumimum Solid capacitor ( 6.3V / 100uF ) is used for the VCOM port.

    Will there be any problems using low ESR parts for the VCOM port?

    The datasheet contains the following:

    In fact, Vcom is being used as the OPAMP's bias voltage as shown in the circuit diagram below.

    Is there any problem with this part?

    Please let me know if there is anything related to what is written in the datasheet.

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    Genius 5240 points

    Hi, TI support team

    Regarding the problem, we share the following.

    1) Condition : Analog in (ADC) -> Speaker no output. (Many identical symptoms occur)

    2) Check items:

    2-1) DIR pin 44 (VCOM) voltage is low, approximately 1.1V.

    2-2) Normal operation when replacing 6.3V / 100uF E-cap (C7612). (dc-offset by 2.5V)

    2-3) It mainly occurs in the initial self-separation and produced PCB ASS’Y.

    2-4) After replacing the E-cap (C7612), it is not reproduced well. (Replace with the same capacity of the same manufacturer)

    2-5) Problem Occurrence Check E-cap unit, no problem such as capacity.

    3) Questions:

    VCOM (reference) voltage problem occurs, what factors can affect it?

    In my experience, there was no problem when using 10uF.

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    TI__Mastermind 24570 points

    Hello MJ, I don't think there is any issue using Polymer Aluminum Solid capacitor.

    However, we  always recommend to use the suggested values for components but one can often get away with few modifications.

    The VCOM pin may be used to bias external circuitry (such as an ADC driver op amp), but the load impedance
    must be high enough because the output impedance of VCOM pin  is typically 12.5 kΩ.

    If you are asking what would be the consequence of using a large cap, then there are several consequences that might effect your circuit. for example it can  give rise to large inrush currents  or  may cause the  source Voltage to droop  a lot . Also a larger capacity cap has  larger ESR or ESL. Excessive resistance and/or inductance in the cap itself will prevent it from being effective at decoupling. Please try to stay within the recommended values of components mentioned in datasheet.

    Regards,

    Arash 

  • 0 in reply to Arash Loloee
    Genius 5240 points

    Dear, Arash

    I have received two questions from customer.

    I would like to inquire about the contents indicated in the responses.

    Q1 ) Is Source Voltage to droop the same as what we inquired about? Or does it mean that it temporarily drops and then rises when the power is turned on?

    Q2 ) What kind of operation inside the IC causes the voltage to drop?

    Thanks.

    Regards,

    MJ

  • 0 in reply to MJ Jeon
    TI__Mastermind 24570 points

    Hi MJ,

    When you connected a very large cap and turn on a power supply, in general you may see a drop and then it will come back up. 

    The VCOM is an unbuffered pin and its getting its value  (VDD/2) internally , however I don't have the visibility to the internal design to tell you the circuitry that is connected to it and how a bigger cap can effect its settling. t if you observe a very large cap at this pin is causing it to give an unexpected voltage , then should  stay with values of datasheet and use the recommended value.

    Regards,

    Arash