Installing Schottkys on a PCB

[Barry]

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.

 

[Robert Baer]

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.

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.