
Detailed Description
The MAX9737 filterless, mono class D audio power
amplifier offers Class AB audio performance and Class
D efficiency with minimal board space. The device
operates from an 8V to 28V supply range.
The MAX9737 features filterless, spread-spectrum
modulation, externally set gain and a low-power shut-
down mode that reduces supply current to less than
1A. Comprehensive click-and-pop suppression and
precharge circuitry reduce noise into and out of shut-
down or mute within 10ms.
Spread-Spectrum Modulation
The MAX9737 features a unique spread-spectrum
switching modulation that flattens EMI wideband spec-
tral components, reducing radiated emissions from the
speaker and cables. The switching frequency of the
Class D amplifier varies randomly by ±4kHz around the
300kHz center frequency. Instead of a large amount of
spectral energy present at multiples of the switching
frequency, the energy is spread over a bandwidth that
increases with frequency. Above a few MHz, the wide-
band spectrum looks like white noise for EMI purposes.
A proprietary amplifier topology ensures this white
noise does not corrupt the noise floor in the audio
bandwidth.
Efficiency
The high efficiency of a Class D amplifier is due to the
output transistors acting as switches and therefore con-
sume negligible power. Power loss associated with the
Class D output stage is due to the MOSFET I2R losses,
switching losses, and quiescent current.
Although the theoretical best efficiency of a linear
amplifier is 78% at peak output power, under typical
music reproduction levels, the efficiency falls to below
40%. The MAX9737 exhibits > 80% efficiency under the
same conditions (Figure 1).
Shutdown
The MAX9737 features a shutdown mode that reduces
power consumption to less than 1A (typ), extending
battery life in portable applications. Drive
SHDN low to
place the device in low-power shutdown mode. In shut-
down mode, the outputs are high impedance and the
common-mode voltage at the output decays to zero.
MAX9737
Mono 7W Class D Amplifier
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7
Pin Description
PIN
NAME
FUNCTION
1, 17, 18
PVDD
Power Supply. Bypass PVDD to PGND with a 1F capacitor connected to pin 1 and a 1F capacitor
connected to pins 17 and 18.
2
CHOLD
Charge-Pump Output. Connect a 1F capacitor to PVDD.
3, 10, 11
AGND
Analog Ground
4
MUTE
Mute Input. Drive MUTE low to place the device in mute mode.
5
SHDN
Shutdown Input. Drive SHDN low to place the part in shutdown mode.
6PC
Input Capacitor Precharge Connection. Connect between input resistor, RIN, and input coupling
capacitor, CIN.
7
IN
Op Amp Inverting Input.
8
PRE
Op Amp Output. PRE is the output of the input operational amplifier.
9
COM
Internal 2.0V Bias. Bypass COM to AGND with a 1F capacitor.
12
REG
Internal 4.2V Bias. Bypass REG to AGND with a 1F capacitor.
13, 14
VS
Internal 5.0V Bias. Bypass VS to AGND with a 1F capacitor.
15
C1N
Charge-Pump, Flying-Capacitor Negative Terminal. Connect C1N to C1P through a 0.1F capacitor.
16
C1P
Charge-Pump, Flying-Capacitor Positive Terminal. Connect C1P to C1N through a 0.1F capacitor.
19, 20
OUT-
Negative Speaker Output
21, 22
PGND
Power Ground
23, 24
OUT+
Positive Speaker Output
—
EP
Exposed Pad. Must be externally connected to PGND.