參數(shù)資料
型號: LM4890LD/NOPB
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 音頻/視頻放大
英文描述: 1 W, 1 CHANNEL, AUDIO AMPLIFIER, DSO10
封裝: LLP-10
文件頁數(shù): 13/30頁
文件大?。?/td> 1621K
代理商: LM4890LD/NOPB
Application Information (Continued)
As stated in the External Components section, R
IN in con-
junction with C
IN create a highpass filter.
C
IN
≥ 1/(2π*20 k*20Hz) = 0.397F; use 0.39F
The high frequency pole is determined by the product of the
desired frequency pole, f
H, and the differential gain, AVD.
With a A
VD = 3 and fH = 100kHz, the resulting GBWP =
300kHz which is much smaller than the LM4890 GBWP of
2.5MHz. This calculation shows that if a designer has a need
to design an amplifier with a higher differential gain, the
LM4890 can still be used without running into bandwidth
limitations.
The LM4890 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli-
cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor (C4) may be
needed as shown in Figure 2 to bandwidth limit the amplifier.
This feedback capacitor creates a low pass filter that elimi-
nates possible high frequency oscillations. Care should be
taken when calculating the -3dB frequency in that an incor-
rect combination of R
3
and C
4
will cause rolloff before
20kHz. A typical combination of feedback resistor and ca-
pacitor that will not produce audio band high frequency rolloff
is R
3 = 20k
and C
4 = 25pf. These components result in a
-3dB point of approximately 320 kHz.
20019224
FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER
LM4890
www.national.com
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