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PCM4202 Input Impedance

KANJI SHIBATANI
Mastermind 6205 points
Other Parts Discussed in Thread: PCM4202


Q1 
Rin of Analog-input is 3Kohm from the PCM4202 data sheet p4, and customer
measured the Rin(between Vin+/Vin-)  by Tester* as Fig1-(c) , result shows 6Kohm ( 3Kohm x 2)
and customer says that  data sheet description is confirmed…..0020.PCM4202_Questions_about_Analog_Input_Question.ppt
Is this reasonable?

If No, would you please let us know the measuring method of
Rin in the data sheet?　（Use Network Analyzer?)

   * Note that power is ON (Vcc=5V/VDD=3.3V) when measuring the Rin by Tester

Q2  
When Customer had directly insert 5V or 0V as Fig1-(a)(b), customer seen 5V or 0V
in the portion of  VIN+ and also VIN- .
Is this reasonable?

In the data sheet  p13, there are description  that  “The PCM4202 analog inputs are internally
biased to  approximately VCC/2.”,,, but  Cusomer’s test result does not show that.
In case of Fig-1-(a)(b), Vcom is Hi-Z?? ( Fig2-(b)  switch is OFF? )

With my best regards

  • 0
    TI__Guru 51346 points

    1: each input has a typ. 3kOhm impedance for a total of 6kOhm

    2: what you measure is expected. Please follow the recommendations in figure 13 and 14. VcomL and VcomR must not be loaded by more than 1MOhm because they can only source a few hundred uAmps.

  • 0 in reply to Dominik Hartl11
    Mastermind 6205 points

    Dear D. Hartl-san

    Thank you for your rely quickly.

    Would you advise  following "  "  is TYPO or not?

    Thank you and with my best regards

    -------------

    VcomL and VcomR "must not be" loaded by more than 1MOhm because they can only source a few hundred uAmps.

    ==> must be ... more than 1Mohm

    ---------------

    Data sheet  p13 describes as following

    Although the VCOML and VCOMR outputs are internally
    buffered, the output current is limited to a few hundred μA.
    It is recommended to connect these pins to external nodes
    with greater than 1MΩ impedance, or to buffer the outputs
    with a voltage follower circuit when driving multiple
    external or low impedance nodes.

     

     

  • 0 in reply to KANJI SHIBATANI
    TI__Guru**** 189399 points

    Shibatani-san,

    Your understanding is correct.

    -d2