max9752aetit Maxim Integrated Products, Inc., max9752aetit Datasheet - Page 13

• Manufacturer Part Number: max9752aetit
• Description: 2.2w, Low-emi, Stereo, Class D Power Amplifiers With Directdrive Headphone Amplifiers
• Manufacturer: Maxim Integrated Products, Inc.

Figure 3. MAX9752/MAX9753/MAX9754 Radiated Emissions with 76mm of Speaker Cable
Figure 4. Second-Generation Class D Output Waveform with
No Signal
The MAX9752/MAX9753/MAX9754 use Maxim’s unique,
patented modulation scheme that eliminates the LC filter
required by traditional Class D amplifiers, improving effi-
ciency, reducing component count, and conserving
board space and system cost (Figure 4). With no input
signal, the outputs are two low-duty-cycle pulses that are
in-phase. This lowers the high-frequency energy and
spectral content. In comparison, conventional Class D
amplifiers output a 50% duty cycle when no input signal
is present. For most applications with short speaker
cables, no filtering is required.
V
OUT_
2.2W, Low-EMI, Stereo, Class D Power Amplifiers
+ - V
V IN_ = 0V
OUT_
OUT_+
OUT_-
- = 0V
Filterless Modulation/Common-Mode Idle
50
45
40
35
30
25
20
15
10
5
0
30
______________________________________________________________________________________
60
with DirectDrive Headphone Amplifiers
80
100
120
140
FREQUENCY (MHz)
160
Efficiency of a Class D amplifier is attributed to the
region of operation of the output stage transistors. In a
Class D amplifier, the output transistors act as switches
and consume negligible power. Any power loss associ-
ated with the Class D output stage is mostly due to the
I
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 (typical music
reproduction levels), efficiency falls below 30%, whereas
the MAX9752/MAX9753/MAX9754 still exhibit > 80%
efficiencies under the same conditions (Figure 5).
Figure 5. MAX9752/MAX9753/MAX9754 Class D Efficiency vs.
MAX9750/MAX9751/MAX9755 Class AB Efficiency
2
R loss of the MOSFET on-resistance, and quiescent
180
200
100
90
80
70
60
50
40
30
20
10
0
0
MAX9752
MAX9753
MAX9754
220
EFFICIENCY vs. OUTPUT POWER
0.5
240
CLASS AB
OUTPUT POWER (W)
1.0
260
280
1.5
R
L
= 8Ω
300
2.0
Efficiency
13