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Installing Schottkys on a PCB

Discussion in 'General Electronics' started by Barry, Mar 1, 2004.

  1. Barry

    Barry Guest

    Hi all,

    I have a Codec PCB board which has the following input circuitry.


    |--------------------------------------------------------
    |
    | AIC23EVM daughterboard
    |
    |
    | 4.9K 0.47uF |------------
    ----/\/\/\/\----|------------|------)|-----| LINEIN
    RCA input | | |
    -----| | | | AIC23
    | | \ | |
    | | / --- 47pF | CHIP
    | | \ 4.9K --- |
    | | / |
    | | | |
    | | | |
    | |----------|------------|
    | |
    | \/ AGND
    |

    The line input on the AIC _chip_ biases itself at 1.5Volts. This chip
    input accepts voltages between 0 and 3.3 Volts. Voltages outside the
    range -0.3 and 3.6Volts could potentially damage the chip according to
    the specs. Therefore I'd like to install schottky clampling diodes,
    backward biased, between the line input after the dc blocking cap
    (0.47uF), and both the ground and 3.3 volt rail. The problem is, this
    requires installing these these diodes onto the PCB board ( a Tex.
    Inst. evaluation module for the AIC23 chip), something I haven't done
    before. I'm a student of Computer Engineerin BTW, but I'm going to get
    a college technician to help me. I was therefore hoping you guys could
    advise me as to how to go about this. On the drill drawings for the
    EVM, there seems to be a region in the top left hand section of the
    board for installing new components - a 7*10 array. This is evident in
    the spec sheet -

    http://www.lami.pucpr.br/~afonso/Graduacao/Outros/Audio/tlv320aic23-manual.pdf

    appendix page 16. I could therefore install the schottkys here and
    bring the ground, 3.3, and line-in to this area also. Does this sound
    like a reasonable approch? What kind of wire might I use to carry the
    rails and line-in to this array?

    I haven't talked to the tech. yet, but I'm sure he can advise me also.

    Hope you can help,

    Barry.
     
  2. Robert Baer

    Robert Baer Guest

    Use surface-mount diodes to conserve space, and perhaps surface-mount
    0.1uF bypass capacitors as close to the input pin as possible.
    One could use #30 wire-wrap wire for the clamp voltages, and (say) #18
    for ground bus-bar going the shortest route to ground.
     
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