MAX9705AETB/V+T Maxim Integrated, MAX9705AETB/V+T Datasheet - Page 11

• Manufacturer Part Number: MAX9705AETB/V+T
• Description: Audio Amplifiers 2.3W Ultra-Low-EMI Filterless Class D Audio Amplifier
• Manufacturer: Maxim Integrated

Specifications of MAX9705AETB/V+T

• Product: Class-D
• Output Power: 950 mW
• Thd Plus Noise: 0.02 %
• Supply Current: 5.4 mA
• Maximum Power Dissipation: 1951.2 mW
• Audio Load Resistance: 4 Ohms
• Common Mode Rejection Ratio (min): 56 dB

Figure 2. MAX9705 Output with an Input Signal Applied (SSM Mode)
The MAX9705 uses Maxim’s unique modulation scheme
that eliminates the LC filter required by traditional
Class D amplifiers, improving efficiency, reducing com-
ponent count, and conserving board space and system
cost. Conventional Class D amplifiers output a 50% duty
cycle square wave when no signal is present. With no fil-
ter, the square wave appears across the load as a DC
voltage, resulting in a finite load current, increasing
power consumption. When no signal is present at the
input of the MAX9705, the outputs switch as shown in
Figure 3. Because the MAX9705 drives the speaker dif-
ferentially, the two outputs cancel each other, resulting
in no net idle-mode voltage across the speaker, minimiz-
ing power consumption.
Efficiency of a Class D amplifier is attributed to the
region of operation of the output stage transistors. In a
Filterless Modulation/Common-Mode Idle
V
V
V
OUT+
IN+
IN-
- V
OUT-
OUT+
OUT-
______________________________________________________________________________________
t
ON(MIN)
2.3W, Ultra-Low-EMI, Filterless,
t
SW
Efficiency
t
SW
Class D Audio Amplifier
Class D amplifier, the output transistors act as current-
steering switches and consume negligible additional
power. Any power loss associated with the Class D out-
put stage is mostly due to the I
on-resistance and supply current.
The theoretical best efficiency of a linear amplifier is
78%; however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9705 still exhibits >70% efficiencies
under the same conditions (Figure 4).
The MAX9705 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9705 in a low-power (0.3µA) shutdown
mode. Connect SHDN to V
t
SW
t
SW
DD
for normal operation.
2
R loss of the MOSFET
Shutdown
11