Front Panel I/O Connectivity Design Guide

plugged into the front panel jack, these return signals which feed that back panel jack are

disconnected, thus muting the back panel output.

Note that the motherboard should not leave the back panel signal floating when front panel devices

are connected. Permitting the back panel signals to float could result in excessive noise at the back

panel jack when the front panel jack is in use.

The motherboard designer should put weak pull-down resistors (10 k , for example) on the

FP_RETURN_R and FP_RETURN_L lines. If using a single supply for the output amplifier,

ensure that these resistors are located after the output capacitor to avoid loading down the amplifier

bias. The grounded side of these pulldowns should be connected to analog ground to prevent

digital noise from entering the audio sub-system.

MIC

AUD_GND

AC’97 Front Panel Dongle Schematic

JACK2 R

JACK2 L

910

JACK1 L

MIC BIAS

FP_OUT_R

FP_OUT_L

FP_RETURN_R

FP_RETURN_L

AUD_5V

MIC Jack

Headphone

Jack

JACK1 L

Normally close shunt springs make

contact with the signal path and

cannot be used for Jack detection.

2X5 Stake Pin Header (100mil Pitch)

** Note: Z

should be 600Ω or greater @ 100MHz with a low Q (broad Impedance curve over frequency)

EMI Filter

220pF

AUD_GND

Figure 2. AC’97 Front Panel Dongle Schematic