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參數(shù)資料
| 型號(hào)： | LM4913MH/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 0.09 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封裝： | TSSOP-10 |
| 文件頁數(shù)： | 6/18頁 |
| 文件大小： | 1078K |
| 代理商： | LM4913MH/NOPB |
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8
Load
Given:
Power Output
1 Wrms
Load Impedance
8
Input Level
1 Vrms
Input Impedance
>20k
Bandwidth
100Hz – 20kHz ± 0.25 dB
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the Typical Performance Charac-
teristics section. Another way, using Equation (8), is to cal-
culate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To account
for the amplifier's dropout voltage, two additional voltages,
based on the Dropout Voltage vs Supply Voltage in the Typ-
ical Performance Characteristics curves, must be added to
the result obtained by Equation (8). The result is Equation (9).
(8)
V
DD = VOUTPEAK + VODTOP + VODBOT
(9)
The Output Power vs. Supply Voltage graph for an 8
load
indicates a minimum supply voltage of 4.6V. The commonly
used 5V supply voltage easily meets this. The additional volt-
age creates the benefit of headroom, allowing the LM4913 to
produce peak output power in excess of 1W without clipping
or other audible distortion. The choice of supply voltage must
also not create a situation that violates of maximum power
dissipation as explained above in the Power Dissipation sec-
tion.
After satisfying the LM4913's power dissipation requirements,
the minimum differential gain needed to achieve 1W dissipa-
tion in an 8
load is found using Equation (10). (RESUME
HERE- All that is left is to discuss the BTL low frequency
phase shift.)
(10)
Thus, a minimum gain of 2.83 allows the LM4913's to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let AV(BTL) = 3. The amplifier's
overall gain is set using the input (Ri), the first stage internal
feedback resistor, and the second stage's fixed gain of 1.25.
With the desired input impedance set at 20k
, the feedback
resistor is found using Equation (11).
R
i = -125k / AV (BTL)
(11)
The value of Ri is 44.2k
. The nominal output power is
1.13W.
The last step in this design example is setting the amplifier's
-3dB frequency bandwidth. To achieve the desired ±0.25dB
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least one-fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the ±0.25dB de-
sired limit. The results are an
f
L = 100Hz / 5 = 20Hz
(12)
and an
f
L = 20kHz x 5 = 100kHz
(13)
As mentioned in the SELECTING EXTERNAL COMPO-
NENTS section, R
i and Ci create a highpass filter that sets the
amplifier's lower bandpass frequency limit. Find the coupling
capacitor's value using Equation (14).
C
i = 1 / 2πRifL
(14)
The result is
1 / 2
π x 44.2k x 20Hz = 0.180F
(15)
Use a 180F capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain AV(BTL), determines
the upper passband response limit. With AV(BTL) = 3 and fH
= 100kHz, the closed-loop gain bandwidth product (GBWP)
is 300kHz. This is less than the LM4913's 3.5MHz GBWP.
With this margin, the amplifier can be used in designs that
require more differential gain while avoiding performance re-
stricting bandwidth limitations.
www.national.com
14
LM4913
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參數(shù)描述 |
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| LM4913MHX/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 1-CH Mono/2-CH Stereo 2W Class-AB 10-Pin TSSOP EP T/R |
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