MAX9741ETN+D Maxim Integrated Products, MAX9741ETN+D Datasheet - Page 10

• Manufacturer Part Number: MAX9741ETN+D
• Description: IC AMP AUDIO PWR 12W STER 56TQFN
• Manufacturer: Maxim Integrated Products
• Type: Class Dr

Specifications of MAX9741ETN+D

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 12W x 2 @ 8 Ohm
• Voltage - Supply: 10 V ~ 25 V
• Features: Depop, Differential Inputs, Mute, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 56-TQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

12W+12W, Low-EMI, Spread-Spectrum,
Stereo, Class D Amplifier
Ferrite beads are available from many manufacturers.
Table 3 lists some manufacturers who make ferrite
beads and other products suitable for use with Class D
amplifiers.
Although they offer a low cost and small size, ferrite
bead filters slightly increase distortion and slightly
reduce efficiency. If the audio performance of the ferrite
bead filters does not meet the system requirements, then
a full inductor/capacitor (LC) filter should be considered.
Using a full inductor and capacitor (LC) output filter
provides significant attenuation of the fundamental
switching energy.
Select inductors rated for the expected RMS current
load. For example, if using a Class D amplifier up to
10W into 8Ω, the inductor should be rated for 1.25A
RMS or more. Furthermore, the inductor should maintain
a constant inductance value across the expected cur-
rent range. Inductors which change in value as a func-
tion of current will cause harmonic distortion.
The output capacitors can also affect audio perfor-
mance. Ceramic capacitors are often selected for their
size and cost advantage, but they cause distortion. If
the application constraints dictate ceramic capacitors,
selecting higher voltage rating and larger package size
mitigates some of the shortcomings. Best performance
is obtained with plastic film capacitors, but these are
larger and more expensive.
In some cases, a Class D amplifier can be used without
an output filter. The intrinsic inductance of the loud-
speaker stores energy from the high-speed PWM pulses,
Table 3. Filter Component Suppliers
10
Murata
Taiyo Yuden
TDK
Fairrite
Coilcraft
Sumida
Panasonic
SUPPLIER
______________________________________________________________________________________
Inductor/Capacitor Output Filters
Ferrite beads,
capacitors
Ferrite beads,
capacitors
Ferrite beads,
capacitors
Ferrite beads
Inductors
Inductors
Inductors
PRODUCT
Filterless Operation
www.murata.com
www.t-yuden.com
www.tdk.co.jp/tetop01
www.fair-rite.com
www.coilcraft.com
www.sumida.com
www.panasonic.com/indu
strial/components
WEBSITE
converting these into power in the audible frequency
range. Filterless operation requires the Class D amplifi-
er to be very close to the speaker. Distances greater
than a few centimeters must be evaluated for EMC
compliance.
Table 4
maximum output power from a given peak input voltage
and given load.
Unlike a Class AB amplifier, the output offset voltage of
Class D amplifiers does not noticeably increase quies-
cent current draw when a load is applied. This is due to
the power conversion of the Class D amplifier. For
example, an 8mVDC offset across an 8Ω load results in
1mA extra current consumption in a Class AB device.
In the Class D case, an 8mV offset into 8Ω equates
to an additional power drain of 8µW. Due to the high
efficiency of the Class D amplifier, this represents an
additional quiescent current draw of: 8µW / (V
η), which is in the order of a few microamps.
The MAX9741 features a differential input structure, mak-
ing them compatible with many CODECs, and offering
improved noise immunity over a single-ended input ampli-
fier. In devices such as PCs, noisy digital signals can be
picked up by the amplifier’s input traces. The signals
appear at the amplifiers’ inputs as common-mode noise. A
differential input amplifier amplifies the difference of the
two inputs, any signal common to both inputs is canceled.
Table 4. Gain Settings
G1
shows the suggested gain settings to attain a
0
0
1
1
G2
0
1
0
1
Input Amplifier
Gain Selection
Differential Input
Output Offset
GAIN (dB)
29.6
19.1
DD
13
16
/ 100
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