MAX9700 Maxim, MAX9700 Datasheet - Page 13

• Manufacturer Part Number: MAX9700
• Description: 1.2W / Low-EMI / Filterless / Class D Audio Amplifier
• Manufacturer: Maxim

Figure 7. Master-Slave Stereo Configuration
Figure 8. Master-Slave THD+N
RIGHT-CHANNEL
LEFT-CHANNEL
DIFFERENTIAL
DIFFERENTIAL
AUDIO INPUT
AUDIO INPUT
1 F
1 F
0.001
0.01
100
0.1
10
1
TOTAL HARMONIC DISTORTION PLUS NOISE
0
V
V
f = 1kHz
R
SLAVE DEVICE
DD
DD
L
______________________________________________________________________________________
= 8
= 3.3V
0.1
V
IN+
IN-
V
IN+
IN-
DD
DD
vs. OUTPUT POWER
OUTPUT POWER (W)
0.2
MAX9700
MAX9700
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 MAX9700s can be configured as a stereo amplifier
(Figure 7). 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 MAX9700s 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 8 and 9). 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 MAX9700 can easily be driven by single-ended
sources (Figure 6), but extra care is needed if the
source impedance “seen” by each differential input is
unbalanced, such as the case in Figure 10a, where the
MAX9700 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 SHDN) depending on the
volume-control setting. As shown, the click-pop perfor-
mance is fine for either max or min volume, but worsens
at other settings.
Figure 9. Master-Slave Crosstalk
-100
-120
-20
-40
-60
-80
0
Designing with Volume Control
10
V
R
f = 1kHz
V
DD
L
IN
= 8
= 500mV
= 3.3V
CROSSTALK vs. FREQUENCY
MASTER-TO-SLAVE
100
SLAVE-TO-MASTER
P-P
FREQUENCY (Hz)
Stereo Configuration
1k
10k
100k
13