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| 型号： | MAX9708ETN+D |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 8/22页 |
| 文件大小： | 0K |
| 描述： | IC AMP AUDIO PWR 42W STER 56TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 37 |
| 类型： | D 类 |
| 输出类型： | 1-通道（单声道）或 2-通道（立体声） |
| 在某负载时最大输出功率 x 通道数量： | 42W x 1 @ 4 欧姆; 21W x 2 @ 8 欧姆 |
| 电源电压： | 10 V ~ 18 V |
| 特点： | 消除爆音，差分输入，静音，短路和热保护，关机 |
| 安装类型： | 表面贴装 |
| 供应商设备封装： | 56-TQFN-EP（8x8） |
| 封装/外壳： | 56-WFQFN 裸露焊盘 |
| 包装： | 管件 |
| 产品目录页面： | 1392 (CN2011-ZH PDF) |
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
16
Maxim Integrated
Auxiliary Heatsinking
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. If an LC filter is used in
the design, placing the inductor in close proximity to the
IC can help draw heat away from the MAX9708.
Thermal Calculations
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:
TA = +40°C
POUT = 16W
Efficiency (
η) = 87%
θJA = 21°C/W
First, the Class D amplifier’s power dissipation must be
calculated:
Then the power dissipation is used to calculate the die
temperature, TC, as follows:
Load Impedance
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 I2R losses in the MOSFETs, which increases
efficiency. To keep the peak currents lower, choose the
highest impedance speaker that can still deliver the
desired output power within the voltage swing limits of
the Class D amplifier and its supply voltage.
Although most loudspeakers fall either 4
Ω or 8Ω, there
are other impedances available that can provide a
more thermally efficient solution.
Another consideration is the load impedance across
the audio frequency band. A loudspeaker is a complex
electro-mechanical system with a variety of resonance.
In other words, an 8
Ω speaker usually has 8Ω imped-
ance within a very narrow range. This often extends
well below 8
Ω, 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 multidriver audio system.
Systems Application Circuit
The MAX9708 can be configured into multiple amplifier
systems. One concept is a 2.1 audio system (Figure 5)
where a stereo audio source is split into three channels.
The left- and right-channel inputs are highpass filtered
to remove the bass content, and then amplified by the
MAX9708 in stereo mode. Also, the left- and right-chan-
nel inputs are summed together and lowpass filtered to
remove the high-frequency content, then amplified by a
second MAX9708 in mono mode.
The conceptual drawing of Figure 5 can be applied to
either single-ended or differential systems. Figure 6
illustrates the circuitry required to implement a fully
differential filtering system. By maintaining a fully differ-
ential path, the signal-to-noise ratio remains uncompro-
mised and noise pickup is kept very low. However,
keeping a fully differential signal path results in almost
twice the component count, and therefore performance
must be weighed against cost and size.
The highpass and lowpass filters should have different
cutoff frequencies to ensure an equal power response
at the crossover frequency. The filters should be at
-6dB amplitude at the crossover frequency, which is
known as a Linkwitz-Riley alignment. In the example
circuit of Figure 6, the -3dB cutoff frequency for the
highpass filters is 250Hz, and the -3dB cutoff frequency
for the lowpass filter is 160Hz. Both the highpass filters
and the lowpass filters are at a -6dB amplitude at
approximately 200Hz. If the filters were to have the
same -3dB cutoff frequency, a measurement of sound
pressure level (SPL) vs. frequency would have a peak
at the crossover frequency.
The circuit in Figure 6 uses inverting amplifiers for their
ease in biasing. Note the phase labeling at the outputs
has been reversed. The resistors should be 1% or better
in tolerance and the capacitors 5% tolerance or better.
TT
P
C
W
C W
C
A
DISS
JA
=+
×
=
° +
× °
=
°
θ
40
24
21
90 4
/.
P
W
WW
DISS
OUT
==
=
.
η
16
087
16
2 4
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX9708ETN-T | 制造商:Maxim Integrated Products 功能描述:20W/40W FILTERLESS, SPREAD-SPECTRUM, MONO/STE - Tape and Reel |
| MAX9708EVKIT | 功能描述:音频放大器 Evaluation Kit for the MAX9708 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| MAX9709ECB+ | 制造商:Maxim Integrated Products 功能描述:AUD AMP SPKR 1CH MONO/2CH STEREO 50W/29W CLS-D 64TQFP EP - Rail/Tube |
| MAX9709ECB+T | 制造商:Maxim Integrated Products 功能描述:AUD AMP SPKR 1CH MONO/2CH STEREO 50W/29W CLS-D 64TQFP EP - Tape and Reel |
| MAX9709ETN | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
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