AD1881A

–23–

REV. 0

1

2

3

4

C3

0.22 F

2.2k

R1

TO CODEC

MIC1 OR MIC2

INPUT

5

FROM CODEC

L1 600Z

L2 600Z

C1

470pF

C2

470pF

EMC COMPONENTS

MIC INPUT

J1

AC-COUPLING

Figure 12. Recommended Microphone Input Connections

R2

10k

R3

100k

PREAMP

AD8531

U1

1

2

3

4

C3

0.22 F

2.2k

R1

TO CODEC

MIC1 OR MIC2

INPUT

5

FROM CODEC

L1 600Z

L2 600Z

C1

470pF

C2

470pF

EMC COMPONENTS

MIC INPUT

J1

AC-COUPLING

C3

0.22 F

AC-COUPLING

MIC BIAS

Figure 13. Microphone with Additional External Preamp (20 dB Gain)

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 k

Ω load, therefore a 1 µF value is recommended to achieve less than

–3 dB roll-off at 20 Hz.

FROM CODEC

LINE_OUT_R

L2 600Z

L1 600Z

C1

470pF

C2

470pF

EMC COMPONENTS

STEREO

LINE_OUT JACK

J1

C1

1 F

1 F

C2

+

+

AC-COUPLING

R1

47k

R2

47k

FROM CODEC

LINE_OUT_L

NOTE: IF AN OUTPUT AMP IS USED,

THE AC-COUPLING CAP VALUES WILL

DEPEND ON THE AMP DESIGN.

Figure 14. Recommended LINE_OUT Connections

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.