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参数资料
| 型号： | TPA2008D2PWPRG4 |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 音频控制 |
| 英文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO24 |
| 封装： | GREEN, PLASTIC, HTSSOP-24 |
| 文件页数： | 6/26页 |
| 文件大小： | 691K |
| 代理商： | TPA2008D2PWPRG4 |
www.ti.com
EFFECTS OF APPLYING A SQUARE WAVE INTO A SPEAKER
Efficiency (theoretical, %)
+ RL RL ) rds(on)
100%
+ 4 (4 ) 0.45)
100%
+ 89.9%
(1)
P
(total)
+ P
O
Efficiency
+ 2.5 W
0.899
+ 2.781 W
(2)
Other losses + P(total)(measured) * P(total) (theoretical) + 3.025 * 2.781 + 0.244 W
(3)
P
(dis) +
0.244 W * (5 V
7 mA) + 0.209 W
(4)
WHEN TO USE AN OUTPUT FILTER
TPA2008D2
SLOS413C – JULY 2003 – REVISED MAY 2004
APPLICATION INFORMATION (continued)
Audio specialists have advised for years not to apply a square wave to speakers. If the amplitude of the
waveform is high enough and the frequency of the square wave is within the bandwidth of the speaker, the
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, does not significantly move the voice coil, as the cone movement is proportional to 1/f2 for
frequencies beyond the audio band.
Damage may occur if the voice coil cannot handle the additional heat generated from the high-frequency
switching current. The amount of power dissipated in the speaker may be estimated by first considering the
overall efficiency of the system. If the on-resistance (rds(on)) of the output transistors is considered to cause the
dominant loss in the system, then the maximum theoretical efficiency for the TPA2008D2 with an 4-
load is as
follows:
The maximum measured output power is approximately 2.5 W with a 5-V power supply. The total theoretical
power supplied (P(total)) for this worst-case condition would therefore be as follows:
The efficiency measured in the lab using a 4-
speaker was 80%. The power not accounted for as dissipated
across the rds(on) may be calculated by simply subtracting the theoretical power from the measured power:
The quiescent supply current at 5 V is measured to be 7 mA. It can be assumed that the quiescent current
encapsulates all remaining losses in the device, i.e., biasing and switching losses. It may be assumed that any
remaining power is dissipated in the speaker and is calculated as follows:
Note that these calculations are for the worst-case condition of 2.5 W delivered to the speaker. Since the
0.209 W is only 7.4% of the power delivered to the speaker, it may be concluded that the amount of power
actually dissipated in the speaker is relatively insignificant. Furthermore, this power dissipated is well within the
specifications of most loudspeaker drivers in a system, as the power rating is typically selected to handle the
power generated from a clipping waveform.
Design the TPA2008D2 without the filter if the traces from amplifier to speaker are short (< 1 inch). Powered
speakers, where the speaker is in the same enclosure as the amplifier, is a typical application for class-D without
a filter.
Many applications require a ferrite bead filter. The ferrite filter reduces EMI around 1 MHz and higher (FCC and
CE only test radiated emissions greater than 30 MHz). When selecting a ferrite bead, choose one with high
impedance at high frequencies, but 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 wires from
the amplifier to the speaker.
14
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