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PCM1773PW How to Use

Sadanori Kato
Guru 36490 points
Other Parts Discussed in Thread: PCM1773

Hi,

Our customers have sevral questions.
Could you please tell us as follows?

Q1. Terminal Processing of Unused Pin
There is described that "But if AIN is not used, AIN must be open and the AMIX terminal must be low." on page 27 of the data sheet.
On the other hand, we found that there is evm schematics on page 21 of evm user's guide,
is jumper to connect one terminal of ac-coupling to gnd.
We believe that to reduce the noise, we should connect the capacitance between AIN and gnd.
When AIN is not used, please tell me the terminal processing that you recommend.

Q2. Bypass Capacitor
There is described that "The 10-uF capacitors must be tantalum or aluminium electrolytic." on page 28 of the data sheet.
If we use REG1117-3.3 that is described on page 19 of the user's guide as the linear regulator,
we believe that we must use tantalum capacitor or aluminium electrolytic capacitor that you recommend.
For example, if we use TPS79633, may we use ceramic capacitor?

Please refer as follow.
http://www.ti.com/lit/ds/slvs351o/slvs351o.pdf

Q3. Digital De-emphasis
What is the purpose of the de-emphasis function?
We believe that by applying de-emphasis for the sound source that performed pre-emphasis processing,
it is a purpose to make both gain of low frequency and gain of high frequency a flat.
Is our opinion correct?
If you have the application note regarding digital de-emphasis, please send us it.

Best Regards,
Kato

  • 0
    Guru 36490 points

    Hi,

    We have obtained a additional question from our customers.
    Could you please tell us as follow?

    Q4. Internal Pull-up/Pull-down Resistor
    Do each digital input terminals have internal pull-up and pull-down resistors?
    If this device does not have them, should we add external pull-up and pull-down registors?
    We could not find it in the evm schematics.

    Best Regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Guru**** 189399 points

    Hi, Kato-san,

    I have asked my colleague to look at your questions.

    -d2

  • 0 in reply to Don Dapkus
    Guru 36490 points

    Hi Don-san,

    Thank you for your cooperation.
    We are looking forward to your reply.

    Best Regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36490 points

    Hi Don-san,

    We are waiting for your response.
    Because our customers are troubled, could you please tell us about them by the morning of December 18 of the Japan time?

    Best Regards,
    Kato

  • 0 in reply to Sadanori Kato
    TI__Intellectual 955 points

    Hello Kato,

    Please find my answer bellow.

    Q1. Terminal Processing of Unused Pin for the PCM1773PW

    If AIN pin is not used, AIN must be OPEN and the AMIX terminal must be LOW. In the EVM schematics, the jumper you saw is if you want to work in MIXING mode (AMIX TERMINAL = HIGH).The mixing mode allows you to mix AIN signal with the outputs signals (VoutL and VoutR). Working in mixing mode, an AC coupling capacitor is needed for AIN so that is why there is this C004.

    Q2. Bypass Capacitor

    Please note that the PCM1773 needs a 2.4V typical analog power supply so you might consider the TPS79625 (fixed 2.5V) instead of the TPS79633 (Fixed 3.3V).
    The datasheet advises to use tantalum or aluminum electrolytic capacitors for the bypass capacitors so you should follow this recommendation for better performances.

    Q3. Digital De-emphasis

    the noise is greater in amplitude at high frenquencies than at lower frequencies. In order to compensate this, the high frequencies of the audio signal are emphasized or boosted in amplitude  with respect to the magnitude of other (usually lower) frequencies before to go thru any transmission system (so before the noise addition). This is pre-emphasis.

     The de-emphasis is the inverse process of pre-emphasis, used to attenuate the amplitude of high frequencies of signal that were boosted before the transmission system. The de-emphasis network, located after the transmission system at the “receiver” section, restores the original amplitude Vs frequency characteristics of the signal thanks to the attenuation. As a result, the noise is attenuated too. The pre-emphasis and de-emphasis produces a more uniform SNR throughout the modulating signal frequency spectrum.

     Q4. Internal Pull-up/Pull-down Resistor

    In general, we recommend you to never let any digital inputs floating, please make sure that you always have the external logic needed.

    Regards

    Wilfried

  • 0 in reply to Wilfried CAPET
    Guru 36490 points

    Hi Wilfried-san,

    Thank you for your cooperation.
    We have sevral questions as follows.
    Could you please tell us as soon as possible?

    Q2. Bypass Capacitor
    Why do you recommend tantalum capacitor or aluminium electrolytic capacitor?
    Our customers would like to know this reason, could you please tell us about it?

    Q4. Internal Pull-up/Pull-down Resistor
    Does this device have internal pull-up and pull-down resistors for digital input terminals?

    Best Regards,
    Kato

  • 0 in reply to Sadanori Kato
    Guru 36490 points

    Hi Wilfried-san,

    We have not obtained your reply yet.
    Because our customers are troubled, could you please comment on them to us as soon as possible?

    Best Regards,
    Kato