max9746 Maxim Integrated Products, Inc., max9746 Datasheet - Page 13

• Manufacturer Part Number: max9746
• Description: Max9746 1.2w, Low-emi, Filterless, Class D Audio Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

Figure 6. Master-Slave Stereo Configuration
Figure 7. Master-Slave THD+N
RIGHT-CHANNEL
LEFT-CHANNEL
DIFFERENTIAL
DIFFERENTIAL
AUDIO INPUT
AUDIO INPUT
1µF
1µF
0.001
0.01
100
0.1
10
1
TOTAL HARMONIC DISTORTION PLUS NOISE
0
V
DD
V
f = 1kHz
R
SLAVE DEVICE
DD
L
______________________________________________________________________________________
= 8Ω
= 3.3V
0.1
V
IN+
IN-
V
IN+
IN-
DD
DD
vs. OUTPUT POWER
OUTPUT POWER (W)
MAX9746
MAX9746
0.2
U1
U2
0.3
SYNC
SYNC
OUT+
OUT+
PV
PV
OUT-
OUT-
DD
DD
0.4
0.5
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Two MAX9746s can be configured as a stereo amplifier
(Figure 6). Device U1 is the master amplifier; its unfil-
tered output drives the SYNC input of the slave device
(U2), synchronizing the switching frequencies of the two
devices. Synchronizing two MAX9746s ensures that no
beat frequencies occur within the audio spectrum. This
configuration works when the master device is in either
FFM or SSM mode. There is excellent THD+N perfor-
mance and minimal crosstalk between devices due to
the SYNC connection (Figures 7 and 8). U2 locks onto
only the frequency present at SYNC, not the pulse
width. The internal feedback loop of device U2 ensures
that the audio component of U1’s output is rejected.
The MAX9746 can easily be driven by single-ended
sources (Figure 5), but extra care is needed if the
source impedance “seen” by each differential input is
unbalanced, such as the case in Figure 9, where the
MAX9746 is used with an audio taper potentiometer
acting as a volume control. Functionally, this configura-
tion works well, but can suffer from click-pop transients
at power-up (or coming out of shutdown) depending on
the volume-control setting. As shown, the click-pop per-
formance is fine for either max or min volume, but wors-
ens at other settings.
Figure 8. Master-Slave Crosstalk
-100
-120
-20
-40
-60
-80
0
10
Designing with Volume Control
V
R
f = 1kHz
V
DD
L
IN
= 8Ω
= 500mV
= 3.3V
CROSSTALK vs. FREQUENCY
MASTER TO SLAVE
100
P-P
FREQUENCY (Hz)
Stereo Configuration
1k
10k
100k
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