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LM4839MTE
LM4839MTE  

Manufacturer Part Number  LM4839MTE 
Manufacturer  National Semiconductor 
LM4839MTE datasheet 

Specifications of LM4839MTE  

Case  TSSOP28  Date_code  2003+ 
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AUDIO POWER AMPLIFIER
DESIGN
Audio Amplifier Design: Driving 1W into an 8
The following are the desired operational parameters:
Power Output:
Load Impedance:
Input Level:
Input Impedance:
Bandwidth:
100 Hz−20 kHz
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 Char
acteristics section. Another way, using Equation (11), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac
count for the amplifier’s dropout voltage, two additional volt
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics curves, must be
added to the result obtained by Equation (11). The result is
Equation (12).
V
(V
+ (V
DD
OUTPEAK
OD TOP
The Output Power vs Supply Voltage graph for an 8
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4839 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 section.
After satisfying the LM4839’s power dissipation require
ments, the minimum differential gain needed to achieve 1W
dissipation in an 8
load is found using Equation (13).
Thus, a minimum overall gain of 2.83 allows the LM4839’s to
reach full output swing and maintain low noise and THD+N
performance.
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The last step in this design example is setting the amplifier’s
−3dB frequency bandwidth. To achieve the desired
pass band magnitude variation limit, the low frequency re
sponse must extend to at least onefifth the lower bandwidth
Load
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
desired limit. The results are an
1 W
RMS
8
1 V
RMS
20 k
and an
±
0.25 dB
As mentioned in the Selecting Proper External Compo
nents section, R
a highpass filter that sets the amplifier’s lower bandpass
frequency limit. Find the coupling capacitor’s value using
Equation (17).
The result is
(10)
Use a 0.39µF capacitor, the closest standard value.
+ V
))
(11)
OD BOT
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain A
load
upper passband response limit. With A
100kHz, the closedloop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4839’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 4 through 8 show the recommended fourlayer PC
board layout that is optimized for the 8pin LQpackaged
LM4839 and associated external components. This circuit is
designed for use with an external 5V supply and 4
ers.
(12)
This circuit board is easy to use. Apply 5V and ground to the
board’s V
DD
speakers between the board’s −OUTA and +OUTA and
OUTB and +OUTB pads.
20
±
0.25dB
±
0.25dB
f
= 100Hz/5 = 20Hz
L
f
= 20kHz x 5 = 100kHz
H
(Right & Left) and C
(Right & Left) create
i
i
C
1/(2 R
f
)
i
i
L
1/(2
*
20k
*
20Hz) = 0.397µF
, determines the
VD
= 3 and f
VD
speak
and GND pads, respectively. Connect 4
(13)
(14)
(15)
(16)
=
H