Product specifications
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Preliminary Revision 0.5, November 19, 1999 Appendix B - Audio Codec and Game/MIDI Port Layout
Guidelines
101
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These high frequency decoupling capacitors should be routed on the component layer with wide traces to reduce impedance and
placed on their respective ground plane.
Low frequency decoupling capacitors (basically greater than or equal to 10uF, Electrolytic or Tantalum) are used to prevent power
supply droop during load transient. These large 10uF low frequency VDD (AVDD or DVDD) decoupling capacitors do not need
to be placed close to the codec, but do need to be placed over the proper ground plane. That is, the DVDD decoupling capacitors
should be placed over digital ground and the AVDD decoupling capacitors should be placed over analog ground. See ground and
power planes section for more information. The low frequency decoupling for the +12V input to the regulator are also over the
digital plane.
Referring to Figure B-2, high frequency decoupling capacitors CM1 and CB4 are placed very near the one pair of AVDD and
AVSS pins (pins 25 and 26) and the other pair of AVDD and AVSS (pins 38 and 42) respectively. The location of low frequency
decoupling capacitors CT5 and CT6 are also close to analog power and ground pins. Similarly, decoupling capacitors CB1, CM2
and CT10 are located very near the digital power and ground (DVDD and DVSS) pins. Decoupling capacitors CB6, and CT3 are
located very near the analog power and ground (VAA and GND) pins of audio amplifier.
Table B-1. Decoupling Capacitor List
Power plane High Frequency Capacitors Low Frequency Capacitors Ferrite Bead Note
AVDD5 CB4, CM1 CT5, CT6 L5, L1
DVDD5 CB1, CM2 CT10 L2
AVDD CB6 CT3 L6
Voltage Reference Bypass and Filter Capacitors
All high frequency decoupling capacitors for the voltage reference should be placed close to the VT1611A chip and routed on the
component layer with wide traces to reduce impedance. The filter capacitors on the VREF, VREFOUT, AFILT1 and AFILT2 pins
should also be top routed and laid close to the codec pins.
Referring to Figure B-2, high frequency decoupling capacitors CB3, C25, C28 and C29 are placed very near the pins VREF,
VREFOUT, AFILT1 and AFILT2 (pins 27, 28, 29 and 30 respectively).
AC-Coupling Capacitors
It is recommended to place all ac-coupling capacitors as close to the device receiving the signal as possible even though they are
not critical. Table B-2 and Table B-3 respectively list the ac-coupling capacitors for audio input and output signals in the example
schematics. When an audio function is not used, the ac-coupling capacitors for it are no longer needed. That is, take away the ac-
coupling capacitors and leave the pins open, such as MIC_IN_2.
Table B-2. AC-Coupling Capacitors for Audio Input Signals
Audio Input Signals AC-Coupling Capacitors Note
CD_L C13 1
CD_R C12 1
CD_GND C14 1
LINE_IN_L C15 1
LINE_IN_R C16 1
PC_BEEP C24 1
MIC_IN_1 C23 1
MIC_IN_2 None 1,2
AUX_IN_L None 1,2
AUX_IN_R None 1,2
VIDEO_L None 1,2
VIDEO_R None 1,2