Datasheet

MAX9742
Single-/Dual-Supply, Stereo 16W,
Class D Amplifier with Differential Inputs
______________________________________________________________________________________ 19
Since each half-bridge output stage is only capable of
driving loads as small as 4Ω and each half-bridge sees
half of the differential load resistance when configured
for BTL, only use the BTL configuration with loads
greater than or equal to 8Ω. The MAX9742 may be ther-
mally limited when using the BTL configuration with
high supply voltages due to the decreased load resis-
tance seen by each half bridge. For optimum perfor-
mance, the PCB should be thermally optimized to
achieve the continuous output powers required for the
application (see the
Thermal Considerations section).
Component Selection
Feedback Capacitor (C
FB_
)
To maximize dynamic range, an external feedback
capacitor (C
FB_
) is needed to generate an error signal
for the Class D modulator. The feedback capacitor con-
figures the input amplifier stage as an integrator whose
output is equal to an error signal consisting of the sum
of the integrated input audio and PWM output signals.
The integrator provides a noise-shaping function for the
closed-loop response of the amplifier.
A
V_BTL
= 2 ×
R
F_
R
IN_
R
IN1
= R
IN2
, R
F1
= R
F2
MID
CLASS D
MODULATOR
AND GATE DRIVE
R
F2
L
F
L
F
R
F2
C
FBR
R
F1
C
ZBL
C
ZBL
R
ZBL
R
ZBL
C
IN
R
IN1
MAX9742
C
IN
R
IN2
R
F1
INL-
INL+
C
IN
R
IN2
C
IN
R
IN1
INR+
INR-
C
FBL
DIFFERENTIAL
AUDIO INPUT
FBL
FBR
C
F
OUTL
V
DD
V
SS
C
F
C
F
C
F
CLASS D
MODULATOR
AND GATE DRIVE
OUTR
V
DD
V
SS
V
OUT_P-P
V
DD
/2
V
DD
/2
V
OUT_P-P
2 x V
OUT_P-P
0V
Figure 7. Input Signal Source and Load Connections for BTL Operation