Datasheet

MAX4409
Application Circuit). Place capacitors C2 and C3 as
close to the device as possible. Route PGND and all
traces that carry switching transients away from SGND
and the traces and components in the audio signal
path.
Ensure that the COM traces have the same trace length
and width as the amplifier input and feedback traces.
Route COM traces away from noisy signal paths. The
thin QFN package features an exposed paddle that
improves thermal efficiency of the package. However,
the MAX4409 does not require additional heatsinking.
Ensure that the exposed paddle is isolated from GND
or V
DD
. Do not connect the exposed paddle to GND
or V
DD
.
80mW, DirectDrive, Stereo Headphone
Amplifier with Common-Mode Sense
14 ______________________________________________________________________________________
V
NOISE
V
NOISE
0.1Ω
0.1Ω
0.1Ω
0.1Ω
V
REF_IN
= (V
NOISE
x 0.99)
V
IN
= V
AUDIO
+ (V
NOISE
x 0.98)
RESISTOR IS
INSERTED
BETWEEN THE
JACK SLEEVE
AND
GND = 9.8Ω
V
AUDIO
V
AUDIO
GND NOISE COMPONENT IN
OUTPUT = V
NOISE
/100
EXAMPLE CONNECTION:
IMPROVEMENT FROM
ADDING MAX4409 WITH
SERIES RESISTANCE
•
•
•
•
9.8Ω RESISTOR ADDS TO HP CROSSTALK, BUT DIFFERENTIAL
SENSING AT THE JACK SLEEVE CORRECTS FOR THIS (ONE CHANNEL
ONLY SHOWN).
CURRENT FLOW (IN SIGNAL CABLE SCREEN) DUE TO V
NOISE
IS GREATLY REDUCED.
NOISE COMPONENT IN THE RECEIVER OUTPUT IS REDUCED BY 34dB
OVER THE PREVIOUS EXAMPLE WITH THE VALUES SHOWN.
•
•
9.8Ω
0.10Ω RESISTANCE FROM CABLE SCREEN
0.10Ω RESISTANCE DUE TO GND CABLING AT RECEIVER
V
NOISE
REPRESENTS THE POTENTIAL DIFFERENCE BETWEEN
THE TWO GNDS
V
REF_IN
= V
NOISE
/2
V
IN
= V
AUDIO
GND NOISE COMPONENT IN
OUTPUT = V
NOISE
/2
MAX4409
Figure 6. Common-Mode Noise Rejection