LM4880M National Semiconductor, LM4880M Datasheet - Page 12

• Manufacturer Part Number: LM4880M
• Description: Audio Power Amplifier IC
• Manufacturer: National Semiconductor

Specifications of LM4880M

• No. Of Channels: 2
• Output Power: 250mW
• Load Impedance: 8ohm
• Operating Temperature Range: -40°C To +85°C
• No. Of Pins: 8
• Termination Type: SMD
• Output Power Pout: 250mW
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Information
ber that the maximum power dissipation value from Equation
(1) must be multiplied by two since there are two indepen-
dent amplifiers inside the package.
Once the power dissipation equations have been addressed,
the required gain can be determined from Equation (4).
From Equation (4), the minimum gain is:: A
Since the desired input impedance was 20 kΩ, and with a
gain of −1.26, a value of 27 kΩ is designated for R
ing 5% tolerance resistors. This combination results in a
nominal gain of −1.35. The final design step is to address the
bandwidth requirements which must be stated as a pair of
−3 dB frequency points. Five times away from a −3 dB point
is 0.17 dB down from passband response assuming a single
pole roll-off. As stated in the External Components section,
A
V
= −R
F
/R
i
(Continued)
V
= −1.26
f
, assum-
(4)
(5)
12
both R
order high pass filters. Thus to obtain the desired frequency
low response of 100 Hz within
taken into consideration. The combination of two single order
filters at the same frequency forms a second order response.
This results in a signal which is down 0.34 dB at five times
away from the single order filter −3 dB point. Thus, a fre-
quency of 20 Hz is used in the following equations to ensure
that the response if better than 0.5 dB down at 100 Hz.
The high frequency pole is determined by the product of the
desired high frequency pole, f
A
kHz, the resulting GBWP = 135 kHz which is much smaller
than the LM4880 GBWP of 12.5 MHz. This figure displays
that if a designer has a need top design an amplifier with a
higher gain, the LM4880 can still be used without running
into bandwidth limitations.
V
C
C
. With a closed-loop gain magnitude of 1.35 and f
i
o
≥ 1/(2π*20kΩ*20Hz) = 0.397 µF; use 0.39 µF
≥ 1/(2π*8Ω*20Hz) = 995 µF; use 1000 µF
i
in conjunction with C
i
, and C
±
H
, and the closed-loop gain,
0.5 dB, both poles must be
o
with R
L
, create first
H
= 100