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參數(shù)資料
| 型號： | TPA2005D1GQYRQ1 |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.45 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA |
| 文件頁數(shù)： | 10/29頁 |
| 文件大小： | 1192K |
| 代理商： | TPA2005D1GQYRQ1 |
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Efficiency: Why You Must Use a Filter With the Traditional Class-D Modulation Scheme
Effects of Applying a Square Wave Into a Speaker
P
SPKR +
P
SUP
–P
SUP THEORETICAL
(at max output power)
(19)
P
SPKR +
P
SUP
P
OUT
–
P
SUP THEORETICAL
P
OUT
(at max output power)
(20)
P
SPKR +
P
OUT
1
hMEASURED *
1
hTHEORETICAL
(at max output power)
(21)
hTHEORETICAL
+
R
L
R
L )
2r
DS(on)
(at max output power)
(22)
When to Use an Output Filter
SLOS474B – AUGUST 2005 – REVISED DECEMBER 2008............................................................................................................................................. www.ti.com
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 × VDD, and the time at each voltage is one-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 TPA2005D1 modulation scheme has very little loss in the load without a filter because the pulses are very
short and the change in voltage is VDD instead of 2 × VDD. 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 than the speaker, resulting in less power
dissipation, which increases efficiency.
If the amplitude of a square wave is high enough and the frequency of the square wave is within the bandwidth
of the speaker, a square wave could cause the voice coil to jump out of the air gap and/or scar the voice coil. A
250-kHz switching frequency, however, is not significant because the speaker cone movement is proportional to
1/f2 for frequencies beyond the audio band. Therefore, the amount of cone movement at the switching frequency
is very small. However, damage could occur to the speaker if the voice coil is not designed to handle the
additional power. To size the speaker for added power, the ripple current dissipated in the load must be
calculated by subtracting the theoretical supplied power, PSUP THEORETICAL, from the actual supply power, PSUP, at
maximum output power, POUT. The switching power dissipated in the speaker is the inverse of the measured
efficiency,
η
MEASURED, minus the theoretical efficiency,ηTHEORETICAL.
The maximum efficiency of the TPA2005D1 with a 3.6-V supply and an 8-
load is 86% from Equation 22. Using
Equation 21 with the efficiency at maximum power (84%), we see that there is an additional 17 mW dissipated in
the speaker. The added power dissipated in the speaker is not an issue as long as it is taken into account when
choosing the speaker.
Design the TPA2005D1 without an output filter if the traces from amplifier to speaker are short. The TPA2005D1
passed FCC and CE radiated emissions with no shielding and with speaker trace wires 100 mm long or less.
Wireless handsets and PDAs are great applications for class-D without a filter.
A ferrite bead filter often can be used if the design is failing radiated emissions without an LC filter, and the
frequency-sensitive circuit is greater than 1 MHz. This is good for circuits that just have to pass FCC and CE
because FCC and CE only test radiated emissions greater than 30 MHz. If choosing a ferrite bead, choose one
with high impedance at high frequencies, but very low impedance at low frequencies.
Use an LC output filter if there are low-frequency (<1 MHz) EMI-sensitive circuits and/or there are long leads
from amplifier to speaker.
18
Copyright 2005–2008, Texas Instruments Incorporated
Product Folder Link(s): TPA2005D1-Q1
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| TPA2005D1ZQYRQ1 | 1.45 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA |
| TPA2005D1GQYR | 1.45 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA15 |
| TPA2005D1DRBR | 1.45 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8 |
| TPA2005D1ZQYRG1 | 1.45 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA15 |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| TPA2005D1-Q1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:1.4-W MONO FILTER-FREE CLASS-D AUDIO POWER AMPLIFIER |
| TPA2005D1TDGNRQ1 | 功能描述:音頻放大器 1.4W Mono Fil-Free Class-D Aud Pwr Amp RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| TPA2005D1ZQYR | 功能描述:音頻放大器 Mono Fully Diff Filter-Free Class-D RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| TPA2005D1ZQYRG1 | 功能描述:音頻放大器 1.4W Mono Class-D Audio Amp RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| TPA2006D1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:1.45-W MONO FILTER-FREE CLASS-D AUDIO POWER AMPLIFIER WITH 1.8-V COMPATIBLE INPUT THRESHOLDS |
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