Texas Instruments 6W Stereo Audio Power Amplifier LM4940TSBD/NOPB LM4940TSBD/NOPB 데이터 시트
제품 코드
LM4940TSBD/NOPB
SNAS219C – OCTOBER 2003 – REVISED MAY 2013
The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired
±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth 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 ±0.25dB-desired limit. The results are
an
±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth 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 ±0.25dB-desired limit. The results are
an
f
L
= 100Hz / 5 = 20Hz
(10)
and
f
L
= 20kHz x 5 = 100kHz
(11)
As mentioned in the
section, R
INA
and C
INA
, as well as C
OUT
and R
L
,
create a highpass filter that sets the amplifier's lower bandpass frequency limit. Find the coupling capacitor's
value using
value using
C
IN
= 1 / 2
π
R
IN
f
L
(12)
The result is
1 / (2
π
x20k
Ω
x20Hz) = 0.398µF = C
IN
(13)
and
1 / (2
π
x 4
Ω
x 20Hz) = 1989µF = C
OUT
(14)
Use a 0.39µF capacitor for C
IN
and a 2000µF capacitor for C
OUT
, the closest standard values.
The product of the desired high frequency cutoff (100kHz in this example) and the differential gain A
V
,
determines the upper passband response limit. With A
V
= 12 and f
H
= 100kHz, the closed-loop gain bandwidth
product (GBWP) is 1.2mHz. This is less than the LM4940'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.
be used in designs that require more differential gain while avoiding performance restricting bandwidth
limitations.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
through
show the recommended two-layer PC board layout that is optimized for the DDPAK-
packaged LM4940 and associated external components. This circuit board is designed for use with an external
12V supply and 4
12V supply and 4
Ω
(min) speakers.
This circuit board is easy to use. Apply 12V and ground to the board's V
DD
and GND pads, respectively. Connect
a speaker between the board's OUT
A
and OUT
B
outputs and their respective GND terminals.
14
Copyright © 2003–2013, Texas Instruments Incorporated
Product Folder Links: