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功放散热设计

更新时间：2019-12-07 13:50:49 大小：487K 上传用户：superfect查看TA发布的资源 标签：功放散热 下载积分：1分 评价赚积分 （如何评价?） 打赏 收藏 评论(1) 举报

资料介绍

功放散热设计，Class D类功放的热设计资料，包括损耗计算，布板说明。

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Application Report  
SLAA880–January 2019  
Thermal design considerations for TAS5805M Class-D  
audio amplifier  
Ella Zhang, Jacky Wang  
ABSTRACT  
The TAS5805M is a high-efficiency, stereo, closed-loop Class-D audio amplifier that can be used in many  
applications such as Smart Speakers, televisions, and so forth. In some real use cases, there are still  
thermal problems in large-output power situations if the design is not carefully considered. Proper  
parameter selection is critical to meet the desired thermal performance in the customer's applications. This  
application report discusses some key factors to be considered in the TAS5805M thermal design, such as  
switching frequency, modulation modes, and PCB layout.  
Contents  
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Class-D Audio Amplifier Overview.........................................................................................
Power Losses Considerations in Class-D Audio Amplifier ............................................................
PCB Layout Considerations...............................................................................................
Summary ....................................................................................................................
References ..................................................................................................................
List of Figures  
1
Typical Block Diagram of Class-D Audio Amplifier......................................................................
Explanation for MOSFET Switching Loss ................................................................................
Explanation for MOSFET Gate Loss......................................................................................
Efficiency vs. Output Power in Different Switching Frequency (BD Mode) ..........................................
PWM Voltage Waveform (50% Duty-Cycle)..............................................................................
PWM Voltage Waveform (50% Duty-Cycle)..............................................................................
PWM Voltage Waveform (50% Duty-Cycle)..............................................................................
PWM Voltage Waveform (50% Duty-Cycle)..............................................................................
1SPW Mode in Large Output Condition ..................................................................................
Efficiency vs. Output Power with Different Modulation Mode (Fsw = 768 kHz) .....................................
Efficiency vs. Output Power with Different PVDD (1SPW Mode) .....................................................
Efficiency vs. Output Power with Different Output Filter (BD mode, Fsw = 384 kHz) ..............................
A Good Example of IC Placement .......................................................................................
An Example of a Radial Cut ..............................................................................................
An Example of a Circular Cut ............................................................................................
Layout Example of TAS5805M (Stereo BTL with Ferrite Bead) .....................................................
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1
SLAA880–January 2019  
Thermal design considerations for TAS5805M Class-D audio amplifier  
Copyright © 2019, Texas Instruments Incorporated  
Class-D Audio Amplifier Overview  
Trademarks  
PowerPAD is a trademark of Texas Instruments.  
All other trademarks are the property of their respective owners.  
1
Class-D Audio Amplifier Overview  
shows the Class-D audio amplifier. This amplifier is a switching amplifier that consists of a pulse  
a power stage, and an output filter. The output of a Class-D amplifier is a PWM (pulse-  
width-modulation) switched signal with duty cycle that is modulated with audio signal. Compared with  
traditional Class-AB audio amplifier, the efficiency of the Class-D amplifier has been significantly  
improved. In some real cases, Class-D audio amplifiers still have thermal problems when the design is not  
good enough. The thermal performance is mainly influenced by power losses and heat dissipation.  
To achieve better thermal performance, the power losses in the Class-D audio amplifier power stage must  
be taken into consideration since the Class-D audio amplifier efficiency is related to MOSFET total power  
losses. These power losses are the results of MOSFET conduction, switching, and gate charge losses.  
Power loss is mainly correlated with efficiency. Generally speaking, the efficiency of a Class-D audio  
amplifier is mainly influenced by the output filter and its ripple current, switching frequency, and power loss  
from the power stage.  
Heat dissipation is mainly affected by PCB layout. PCB contributes up to 80-90% of heat dissipation for  
thermally attached devices. The tips of PCB layout for TAS5805M is discussed in this application report.  
PWM Modulator  
Demodulate  
through low-pass  
filter  
Signal Out  
Ramp  
œ
+
œ
+
Signal In  
Comparator  
Figure 1. Typical Block Diagram of Class-D Audio Amplifier  
This report uses TAS5805M as an example to discuss thermal design considerations in Class-D audio  
amplifiers. The report analyzes the thermal problems in TAS5805M from two aspects: power losses and  
heat dissipation. To reduce power losses, some factors need to be taken into account, such as switching  
frequency, modulation mode, and output filter selection of TAS5805M. Thermal performance is also  
related to heat dissipation. For better thermal performance, the PCB layout must be designed properly to  
minimize the thermal impedance and achieve the best balance of thermal and electrical electromagnetic  
performance.  
2
Thermal design considerations for TAS5805M Class-D audio amplifier  
SLAA880–January 2019  
Copyright © 2019, Texas Instruments Incorporated  
 

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