Datasheet
MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 13
sent at the input of the MAX9759, the outputs switch as
shown in Figure 4. Because the MAX9759 drives the
speaker differentially, the two outputs cancel each other,
resulting in no net Idle Mode™ voltage across the
speaker and minimal power consumption.
Efficiency
Efficiency of a Class D amplifier is mostly associated
with the region of operation of the output stage transis-
tors. In a Class D amplifier, the output transistors act as
current-steering switches and consume negligible addi-
tional power. Any power loss associated with the Class
D output stage is mostly due to the I x R loss of the
MOSFET on-resistance and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%; however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (i.e., typi-
cal music reproduction levels), efficiency of a linear
amplifier can fall below 30%. The MAX9759 Class D
amplifier still exhibits >90% efficiencies under the same
conditions (Figure 5).
Gain Selection
The MAX9759 features an internally set, logic-selec-
table gain. The G1 and G2 logic inputs set the gain of
the MAX9759 speaker amplifier (Table 2).
Shutdown
The MAX9759 features a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low places the MAX9759 in a low-power (0.1µA)
shutdown mode. Drive SHDN high for normal operation.
30 60 80 100 120 140 160 180 280 300220200 240 260
15
20
25
30
35
40
45
50
AMPLITUDE (dBµV/m)
FREQUENCY (MHz)
MAX9759
OUTPUT SPECTRUM
FCC LIMIT
Figure 3. MAX9759 EMI Spectrum
V
IN
= 0V
OUT-
OUT+
V
OUT+
- V
OUT-
= 0V
Figure 4. MAX9759 Outputs with No Input Signal
0
30
20
10
50
40
90
80
70
60
100
0 0.2 0.4 0.8 1.20.6 1.0
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
V
DD
= 5V
f = 1kHz
R
L
= 8Ω
CLASS AB
MAX9759
Figure 5. MAX9759 Efficiency vs. Output Power
G2 G1 GAIN (dB)
00+24
01+18
10+12
11 +6
Table 2. Gain Selection
Idle Mode is a trademark of Maxim Integrated Products, Inc.