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| 型号： | TPA3117D2RHBT |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频／视频放大 |
| 英文描述： | AUDIO AMPLIFIER, PQCC32 |
| 封装： | 5 X 5 MM, GREEN, PLASTIC, QFN-32 |
| 文件页数： | 11/30页 |
| 文件大小： | 850K |
| 代理商： | TPA3117D2RHBT |
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SLOS672 – OCTOBER 2010
Also, it is important that the ferrite bead is large enough to maintain its impedance at the peak currents expected
for the amplifier. Some ferrite bead manufacturers specify the bead impedance at a variety of current levels. In
this case it is possible to make sure the ferrite bead maintains an adequate amount of impedance at the peak
current the amplifier will see. If these specifications are not available, it is also possible to estimate the bead
current handling capability by measuring the resonant frequency of the filter output at low power and at maximum
power. A change of resonant frequency of less than fifty percent under this condition is desirable. Examples of
ferrite beads which have been tested and work well with the TPA3117D2 include 28L0138-80R-10 and
HI1812V101R-10 from Steward and the 742792510 from Wurth Electronics.
A high quality ceramic capacitor (x5R or better) is also needed for the ferrite bead filter. A low ESR capacitor with
good temperature and voltage characteristics will work best.
Additional EMC improvements may be obtained by adding snubber networks from each of the class D outputs to
ground. Suggested values for a simple RC series snubber network would be 10
in series with a 330 pF
capacitor although design of the snubber network is specific to every application and must be designed taking
into account the parasitic reactance of the printed circuit board as well as the audio amp. Take care to evaluate
the stress on the component in the snubber network especially if the amplifer is running at high PVCC. Also,
make sure the layout of the snubber network is tight and returns directly to the PGND or the thermal pad beneath
the chip.
Efficiency: LC Filter Required With the Traditional Class-D Modulation Scheme
The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform results
in maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current is
large for the traditional modulation scheme, because the ripple current is proportional to voltage multiplied by the
time at that voltage. The differential voltage swing is 2 × VCC, and the time at each voltage is half the period for
the traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half cycle for
the next half cycle, while any resistance causes power dissipation. The speaker is both resistive and reactive,
whereas an LC filter is almost purely reactive.
The TPA3117D2 modulation scheme has little loss in the load without a filter because the pulses are short and
the change in voltage is VCC instead of 2 × VCC. As the output power increases, the pulses widen, making the
ripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for most
applications the filter is not needed.
An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flow
through the filter instead of the load. The filter has less resistance but higher impedance at the switching
frequency than the speaker, which results in less power dissipation, therefore increasing efficiency.
When to Use an Output Filter for EMI Suppression
The TPA3117D2 has been tested with a simple ferrite bead filter for a variety of applications including long
speaker wires up to 125 cm and high power. The TPA3117D2 EVM passes FCC Class B specifications under
these conditions using twisted speaker wires. The size and type of ferrite bead can be selected to meet
application requirements. Also, the filter capacitor can be increased if necessary with some impact on efficiency.
There may be a few circuit instances where it is necessary to add a complete LC reconstruction filter. These
circumstances might occur if there are nearby circuits which are sensitive to noise. In these cases a classic
second order Butterworth filter similar to those shown in the figures below can be used.
Some systems have little power supply decoupling from the AC line but are also subject to line conducted
interference (LCI) regulations. These include systems powered by "wall warts" and "power bricks." In these
cases, an LC reconstruction filter can be the lowest cost means to pass LCI tests. Common mode chokes using
low frequency ferrite material can also be effective at preventing line conducted interference.
Copyright 2010, Texas Instruments Incorporated
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Product Folder Link(s) :TPA3117D2
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相关代理商/技术参数 |
参数描述 |
|---|---|
| TPA3117D2RHBT | 制造商:Texas Instruments 功能描述:; Amplifier Class:D; No. of Channels:2; 制造商:Texas Instruments 功能描述:IC, AUDIO PWR AMP, CLASS D 15W QFN-32 |
| TPA3118D2 | 制造商:TI 制造商全称:Texas Instruments 功能描述:15W,30W,50W Filter-Free Class-D Stereo Amplifier Family with AM Avoidance |
| TPA3118D2DAP | 功能描述:音频放大器 50W Stereo Class-D Audio Amp 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 |
| TPA3118D2DAPR | 功能描述:音频放大器 50W Stereo Class-D Audio Amp 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 |
| TPA3118D2EVM | 功能描述:音频 IC 开发工具 TPA3118D2 Eval Mod RoHS:否 制造商:Texas Instruments 产品:Evaluation Kits 类型:Audio Amplifiers 工具用于评估:TAS5614L 工作电源电压:12 V to 38 V |
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