Datasheet

MAX9742
Single-/Dual-Supply, Stereo 16W,
Class D Amplifier with Differential Inputs
28 ______________________________________________________________________________________
T-Network for Low THD Performance
at Low Output Powers (Optional)
If low THD+N performance is needed at low-output pow-
ers, replace the feedback resistor (R
F1
) in each channel
with the T-network shown in Figure 15. The T-network
provides additional attenuation of audio band noise,
therefore, providing improved THD+N performance at
lower output powers. Use the following expressions to
select R
IN1
, R
IN2
, R
F1a
, R
F1b
, and R
F2
:
where A
V
is the desired voltage gain in V/V. To maxi-
mize CMRR and minimize gain mismatch between
channels, use the closest 1% tolerance resistor values
available for R
IN1
, R
IN2
, R
F1a
, R
F1b
, and R
F2
.
See the THD+N vs. Output Power With and Without
T-Network plot in the Typical Operating Characteristics
for a comparison of the THD+N performance with and
without the optional T-network.
Output Limiting Diodes (Optional)
In applications where the output can be driven to clip-
ping, a pair of diodes around the feedback capacitor
helps reduce distortion. Clipping is most likely to hap-
pen when driving high-impedance speakers with lower
supply voltages, for example, 8Ω loads with a 24V sin-
gle supply. Diodes such as BAV99, a dual series silicon
switching diode, are a good choice. Connect these
diodes around the feedback capacitor as shown in
Figure 16.
R
RR
A
kk
A
683k
A
RR
RR R
IN1
F1a F1b
VVV
IN1 IN2
F2 F1a F1b
()
()
()
=
+
=
+
=
=
=+
121 562ΩΩ Ω
Ω
Ω
Ω
TO OUT_
C
IN
R
IN1
MAX9742
C
IN
R
IN2
TO CLASS D
MODULATOR
IN_-
IN_+
FB_
R
F1a
121kΩ
R
F1b
562kΩ
C
FB_1
150pF
C
FB_2
10pF
C
FB_1
150pF
R
F2
681kΩ
NEGATIVE
AUDIO INPUT
POSITIVE
AUDIO INPUT
TO MID
A
V
=
R
F1a
+ R
F1b
R
IN1
R
F2
= R
F1a
+ R
F1b
= 688kΩ
R
IN1
= R
IN2
Figure 15. Optional T-Network for Minimizing THD+N at Low Output Powers
C
FB_
TO FB_TO IN_-
Figure 16. Connection of Output Limiting Diodes