CRD4299-1 AMR
down to a clean +5 V analog supply. Two packag-
ing options are supported, where U5 is an SO8 sur-
face mount package and U4 is a TO-92 pin-in-hole
package. The -12 V power pin is decoupled
through C73/C74, and supplies power to the head-
phone circuit.
common return path for both the left and right
channels. Therefore, the input impedance of this
block is half of that of the other inputs.
The modem connection is both a mono input and
output. The output is fed from the CS4299’s
MONO_OUT pin through a divider made of
R22/23. The divider ratio is preset to 0 dB for an
output voltage of 1 Vrms. If a lower output voltage
is desired, the resistors can be replaced with appro-
priate values, as long as the total load on the output
is kept greater than 10 kΩ. The input is not divided
to accommodate line level sources up to 1 Vrms.
3.4 Figure
14
: CS4299
AC ‘97
Audio Codec
For the best audio performance, the analog voltage
regulator, an MC78L05, is located near the
CS4299. A 10 µF electrolytic capacitor should be
added next to pins 25 and 26 if the capacitor con-
nected to the output of the power regulator is locat-
ed far away from the CS4299. All filtering
capacitors of audio signals are NPO-type to ensure
minimal added distortion. Two footprints are pro-
vided for the crystal: a CA-301 pin-in-hole foot-
print, Y1, for miniature crystal; and a short height
HC-49S package, Y2. R47 is a termination resistor
in the serial AC-link between the CS4299 and the
AMR bus.
3.6 Figure
16
: Audio Outputs
The line out is driven directly by the CS4299. The
headphone out amplifier, a Motorola MC1458, is
capable of driving stereo headphones with imped-
ances greater than 32
Ω
or powered speakers.
R37/38 are added for short-circuit protection. An
optical S/PDIF (IEC 958 consumer) output is also
supported.
3.5 Figure
15
: Analog Inputs
The inputs for AUX, VIDEO, CD, and LINE are
passed through voltage dividers that reduce the lev-
els by 6 dB to allow connection of line level sourc-
es up to 2 Vrms. The 220 pF capacitors are
provided on Line_In, Mic_In, CD_In, Aux_In,
Video_In, and Internal Modem connection for
EMC suppression. These may be removed if EMC
testing determines they are not required. 1 µF AC-
coupling capacitors are used on the Line_In,
Mic_In, CD_In, Aux_In, Video_In, and Internal
Modem circuit to minimize the low frequency roll-
off. The internal CD audio connection utilizes a
pseudo-differential interface with CD_GND as the
3.7 Figure
17
: Microphone Pre-amp and
Bias
A Motorola MC33078D low noise dual op-amp
provides an +18 dB gain stage for the microphone
and buffers the phantom power supply for the mic.
The phantom power is derived from the +5 V ana-
log supply and buffered by U1A to provide a max-
imum of 4.2 V with no load and a minimum of
2.0 V under a 0.8 mA load on the ring. Hardware
rolloffs were implemented at 60 kHz and 15 kHz as
recommended by the
PC 99 System Design Guide,
Chapter 17, Audio Components [5].
DS319RD1A1
7
CIRRUS [ CIRRUS LOGIC ]
