參數(shù)資料
型號(hào): LM4874MH/NOPB
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 音頻/視頻放大
英文描述: 2.6 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20
封裝: TSSOP-20
文件頁(yè)數(shù): 10/21頁(yè)
文件大?。?/td> 869K
代理商: LM4874MH/NOPB
Application Information (Continued)
As mentioned in the External Components section, the inter-
nal input resistor and C
i create a high pass filter that sets the
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (11).
f
-3dB = 1/2
π(20k)C
I
(11)
The result is (using the minimum R
IN resistor value to ensure
correct magnitude response at 20Hz)
1/(2
π*20k*20Hz) = 0.398F
(12)
Use a 0.39F capacitor, the closest standard value. The
product of the desired high frequency cutoff (100kHz in this
example) and the differential gain, A
VD, determines the up-
per passband response limit. With A
VD = 3.2 and fH =
100kHz, the closed-loop gain bandwidth product (GBWP) is
320kHz. This is less than the LM4874’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance-restricting
bandwidth limitations.
Recommended Printed Circuit
Board Layout
Figures 2 through 6 show the recommended four-layer PC
board layout that is optimized for the 20-pin MH-packaged
LM4874 and associated external components. This circuit is
designed for use with an external 5V supply and 3
(or
higher) speakers (or load resistors).
This circuit board is easy to use. Apply 5V and ground to the
board’s V
DD
and GND terminals, respectively. Connect
speakers (or load resistors) between the board’s -OUTA and
+OUTA and -OUTB and +OUTB pads. Apply balanced dif-
ferential stereo input signals to the input pins labeled ’-INA,’
’+INA,’ ’-INB,’ and ’+INB.’
200469D7
FIGURE 2. Recommended MH PC Board Layout:
Component-Side Silkscreen
200469D8
FIGURE 3. Recommended MH PC Board Layout:
Component-Side Layout
LM4874
www.national.com
18
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