MAX9704ETJ+ Maxim Integrated Products, MAX9704ETJ+ Datasheet - Page 13

• Manufacturer Part Number: MAX9704ETJ+
• Description: IC AMP AUDIO PWR 16W STER 32TQFN
• Manufacturer: Maxim Integrated Products
• Type: Class Dr

Specifications of MAX9704ETJ+

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 16W x 2 @ 16 Ohm
• Voltage - Supply: 10 V ~ 25 V
• Features: Depop, Differential Inputs, Mute, Short-Circuit and Thermal Protection, Shutdown
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Product: Class-D
• Output Power: 10 W
• Common Mode Rejection Ratio (min): 60 dB
• Thd Plus Noise: 0.07 %
• Supply Current: 24 mA
• Maximum Power Dissipation: 2963 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Audio Load Resistance: 8 Ohms
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Additional improvements are possible if all the traces
from the device are made as wide as possible. Although
the IC pins are not the primary thermal path of the pack-
age, they do provide a small amount. The total improve-
ment would not exceed about 10%, but it could make the
difference between acceptable performance and ther-
mal problems.
If operating in higher ambient temperatures, it is possible
to improve the thermal performance of a PC board with
the addition of an external heatsink. The thermal resis-
tance to this heatsink must be kept as low as possible to
maximize its performance. With a bottom-side exposed
pad, the lowest resistance thermal path is on the bottom
of the PC board. The topside of the IC is not a significant
thermal path for the device, and therefore is not a cost-
effective location for a heatsink.
The die temperature of a Class D amplifier can be esti-
mated with some basic calculations. For example, the
die temperature is calculated for the below conditions:
First, the Class D amplifier’s power dissipation must be
calculated.
Then the power dissipation is used to calculate the die
temperature, T
• T
• P
• R
• Efficiency (η) = 87%
• θ
P
DISS
JA
A
OUT
L
= +40°C
= 16Ω
= 27°C/W
=
= 2x8W = 16W
P
OUT
C
η
, as follows:
T
C
______________________________________________________________________________________
−
= 40°C + 2.4W x 27°C/W
= T
= 104.8°C
P
OUT
A
+ P
Spread-Spectrum, Class D Amplifiers
Auxiliary Heatsinking
Thermal Calculations
DISS
=
16
0 87
.
x θ
W
10W Stereo/15W Mono, Filterless,
JA
−
16
W
=
2 4
.
W
Decreasing the ambient temperature or reducing θ
improve the die temperature of the MAX9704. θ
be reduced by increasing the copper size/weight of the
ground plane connected to the exposed paddle of the
MAX9704 TQFN package. Additionally, θ
reduced by attaching a heatsink, adding a fan, or mount-
ing a vertical PC board.
The on-resistance of the MOSFET output stage in Class
D amplifiers affects both the efficiency and the peak-cur-
rent capability. Reducing the peak current into the load
reduces the I
ing efficiency. To keep the peak currents lower, choose
the highest impedance speaker which can still deliver
the desired output power within the voltage swing limits
of the Class D amplifier and its supply voltage.
Although most loudspeakers are either 4Ω or 8Ω, there
are other impedances available which can provide a
more thermally efficient solution.
Another consideration is the load impedance across the
audio frequency band. A loudspeaker is a complex
electromechanical system with a variety of resonances.
In other words, an 8Ω speaker is usually only 8Ω imped-
ance within a very narrow range, and often extends well
below 8Ω, reducing the thermal efficiency below what is
expected. This lower-than-expected impedance can be
further reduced when a crossover network is used in a
multi-driver audio system.
To optimize the efficiency of the MAX9703/MAX9704,
load the output stage with 12Ω to 16Ω speakers. The
MAX9703/MAX9704 exhibits highest efficiency perfor-
mance when driving higher load impedance (see the
Typical Operating Characteristics). If a 12Ω to 16Ω load
is not available, select a lower supply voltage when dri-
ving 6Ω to 10Ω loads.
Optimize MAX9703/MAX9704 Efficiency with
2
R losses in the MOSFETs, thereby increas-
Load Impedance and Supply Voltage
Load Impedance
JA
can be
JA
JA
can
will
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