Table B-1. Decoupling Capacitor List; Table B-2. Ac-Coupling Capacitors For Audio Input Signals - VIA Technologies Apollo Pro133A Design Manual

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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.

Power plane

AVDD5

DVDD5

AVDD

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.

Preliminary Revision 0.5, November 19, 1999

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