LM4868MT National Semiconductor, LM4868MT Datasheet - Page 19

• Manufacturer Part Number: LM4868MT
• Description: Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function
• Manufacturer: National Semiconductor

Application Information
and an
As mentioned in the Selecting Proper External Compo-
nents section, R
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (12).
The result is
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
1/(2π
i
and C
f
H
*
f
= 20kHz x 5 = 100kHz
L
20kΩ
i
= 100Hz/5 = 20Hz
create a highpass filter that sets the
C
i
≥ 1/(2πR
*
20Hz) = 0.397µF
i
f
L
FIGURE 9. Recommended LQ PC Board Layout:
)
VD
(Continued)
, determines the
Component-Side Silkscreen
(12)
(13)
(14)
(15)
19
upper passband response limit. With A
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4868’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 9 through 13 show the recommended four-layer PC
board layout that is optimized for the 24-pin LQ-packaged
LM4868 and associated external components. Figures 14
through 18 show the recommended four-layer PC board
layout that is optimized for the 24-pin MTE-packaged
LM4868 and associated external components. Figures 19
through 21 show the recommended two-layer PC board
layout that is optimized for the 20-pin MT-packaged LM4868
and associated external components. These circuits are de-
signed for use with an external 5V supply and 4Ω speakers
(or greater) for the MT-packaged LM4868 or 3Ω speakers (or
greater) for the LQ- and MTE-packaged LM4868.
These circuit boards are easy to use. Apply 5V and ground to
the board’s V
speakers between the board’s −OUTA and +OUTA and
OUTB and +OUTB pads.
DD
and GND pads, respectively. Connect 4Ω
20026778
VD
= 3 and f
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