lm4874mh National Semiconductor Corporation, lm4874mh Datasheet - Page 18

• Manufacturer Part Number: lm4874mh
• Description: 2.1w Differential Input, Btl Output Stereo Audio Amplifier With Selectable Gain And Shutdown
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
As mentioned in the External Components section, the inter-
nal input resistor and C
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (11).
The result is (using the minimum R
correct magnitude response at 20Hz)
Use a 0.39µF capacitor, the closest standard value. The
product of the desired high frequency cutoff (100kHz in this
example) and the differential gain, A
per passband response limit. With A
100kHz, the closed-loop gain bandwidth product (GBWP) is
1/(2π
f
*
-3dB
20kΩ
i
create a high pass filter that sets the
= 1/2π(20kΩ)C
*
20Hz) = 0.398µF
IN
resistor value to ensure
VD
FIGURE 2. Recommended MH PC Board Layout:
FIGURE 3. Recommended MH PC Board Layout:
, determines the up-
VD
I
(Continued)
= 3.2 and f
Component-Side Silkscreen
Component-Side Layout
(12)
(11)
H
=
18
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 3Ω (or
higher) speakers (or load resistors).
This circuit board is easy to use. Apply 5V and ground to the
board’s V
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.’
DD
200469D8
200469D7
and GND terminals, respectively. Connect