WM9710

Production Data

w

PD Rev 4.0 December 2003

17

PIN 45 CID0

ID

SELECTED

PRIMARY OR

SECONDARY

BITCLK

NC or pull-up

0

Primary

Output

Ground

1

Secondary

Input

Table 3 Codec ID Selection

HEADPHONE DRIVE AND HEADSET AUTODETECT

Headphone drive capability is provided on HPOUT (pins 39 and 41) and on MONOOUT (pin 37).

Headphones of impedance typically from 16

Ω upwards may be connected to these pins. AC

coupling with an appropriately sized capacitor is recommended for removal of the mid-rail DC

pedestal present on these outputs. AC’97 rev2.2 specification recommends 32

Ω headphones; if a

headphone is connected for use as a headset, where the stereo ear-pieces are driven in parallel,

then each capsule must be of minimum 32

Ω impedance.

In many applications it is desirable to be able to connect either a stereo headphone to the

headphone output pins, or a mono headset, comprising ear-piece(s) and a microphone. The

microphone signal is sent via the tip connected wire of the typical 3-wire jack. In this event it is

desirable to be able to auto-detect the connection of either the headphone or the headset (with

microphone). The main characteristic of the headset and microphone compared to the

headphone is that the microphone impedance is typically much higher than the headphone

capsule (assuming a typical moving coil headphone). Because of this it is possible to connect a

weak pull-up to the tip connection of the headphone jack.

When a headphone is connected the low impedance to ground of the headset pulls down the DC

level to near ground. If a headset with microphone is plugged in, the high impedance of the

microphone does not pull down the DC level on the tip connection, the DC on this pin now rising

to near positive supply. This change in DC level is detected, so allowing detection of change from

headphone to microphone, (or nothing plugged in of course). When this event is detected, the

headphone amplifier that drives the tip connection is turned off, and the signal on this pin is

routed instead to the MIC1 input as a microphone input.

This auto-detect comparator is enabled by setting bit HSCMP. The pull-up current is enabled by

setting bit MPUEN in register 5Ch and also toggles the interrupt signal on the HSDET pin. When

bit HSDT is set the mic1 input is connected to a comparator with a threshold set at mid-rail.

When the comparator output is low, then the headphone driver is enabled. When the comparator

output goes high (that is the pull-up current multiplied by the external impedance to ground on the

mic1 pin is greater than mid-rail), the headphone amplifier is turned off and the mic1 signal is

taken internally from the headphone output pin (39).

RIGHT

MIXER

HPOUTL

HPOUTR

L

R

LEFT

MIXER

HPGND

HEAD

PHONE

MIC

UP: MONO HEADSET WITH MIC

DOWN: STEREO HEADPHONE

HSEN

reg 5Ch

MIC1

MIC2

OFF

(hi-Z)

'1'

'0'

HSDT

reg 5Ch

INTERNAL

MIC

MIC AMP

'1'

'0'

MPUEN

reg 5Ch

5mA

VMID

HSCP

reg 5Ch

HSDET

HPVOL

reg 04h

MS

reg 20h

+

-

HSCMP

reg 5Ch

Figure 10 Headset Autodetect