ad1881a Analog Devices, Inc., ad1881a Datasheet - Page 23

• Manufacturer Part Number: ad1881a
• Description: Ac?97 Soundmax Codec
• Manufacturer: Analog Devices, Inc.

LINE OUTPUT CONNECTIONS
The AD1881A Codec provides stereo LINE_OUT signals at a standard 1 V rms level. These signals must be ac-coupled before they
can be connected to an external load. After the ac-coupling, a minimal resistive load is recommended to keep the capacitors properly
biased and reduce click and pop when plugging stereo equipment into the output jack. The capacitor values should be selected
to provide a desired frequency response, taking into account the nominal impedance of the external load. To meet the PC99
specification for PCs, testing must be performed with a 10 kΩ load, therefore a 1 µF value is recommended to achieve less than
–3 dB roll-off at 20 Hz.
USING AN EXTERNAL HEADPHONE/POWER AMP
The SSM2250 Power Amplifier is an ideal companion for the AD1881A. The amplifier can provide up to 250 mW output in stereo
mode and up to 1.5 W into a mono speaker connected in a bridge-tied load (BTL) configuration.
The SM2250 has a mode control pin that can be used to switch between the stereo output mode and the mono BTL speaker.
Figure 15 shows a typical PC configuration where the SSM2250 drives a set of stereo headphones or external speakers, as well as an
internal mono speaker. One of the normalizing pins on the stereo jack senses the stereo plug insertion and automatically switches
from driving the internal mono speaker to driving the external stereo load.
To conserve power, the SSM2250 can be shut down by the EAPD pin on the AD1881A, using proper power management software.
This is particularly important for portable applications. In shutdown mode, the SSM2250 consumes only 60 µA.
MIC INPUT
J1
1
2
3
4
5
L1 600Z
L2 600Z
LINE_OUT JACK
EMC COMPONENTS
J1
MIC INPUT
J1
470pF
STEREO
C2
470pF
1
2
3
4
5
C1
L2 600Z
EMC COMPONENTS
L1 600Z
L1 600Z
EMC COMPONENTS
L2 600Z
470pF
AC-COUPLING
MIC BIAS
C2
0.22 F
470pF
470pF
2.2k
C3
R1
C2
C1
470pF
C1
NOTE: IF AN OUTPUT AMP IS USED,
THE AC-COUPLING CAP VALUES WILL
DEPEND ON THE AMP DESIGN.
10k
R2
R1
47k
AC-COUPLING
PREAMP
0.22 F
2.2k
R2
47k
+5AV
C3
R1
100k
AC-COUPLING
R3
DD
AD8531
U1
1 F
1 F
C2
C1
+
+
TO CODEC
MIC1 OR MIC2
INPUT
FROM CODEC
V
REFOUT
FROM CODEC
LINE_OUT_R
FROM CODEC
LINE_OUT_L
AC-COUPLING
0.22 F
C3
TO CODEC
MIC1 OR MIC2
INPUT
FROM CODEC
V
REFOUT
AD1881A