LM4927SDBD National Semiconductor, LM4927SDBD Datasheet - Page 12

• Manufacturer Part Number: LM4927SDBD
• Description: BOARD EVALUATION LM4927SD
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4927SDBD

• Amplifier Type: Class AB
• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 2.5W x 1 @ 4 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4927
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Application Information
Since the same variations can have a significant effect on
PSRR and CMRR performance, it is highly recommended
that the input resistors be matched to 1% tolerance or better
for best performance.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8Ω Audio Amplifier
A designer must first determine the minimum supply rail to
obtain the specified output power. The supply rail can easily
be found by extrapolating from the Output Power vs Supply
Voltage graphs in the Typical Performance Characteris-
tics section. A second way to determine the minimum supply
rail is to calculate the required V
add the dropout voltages. Using this method, the minimum
supply voltage is (Vopeak + (V
V
Given:
DO BOT
Tolerance
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
20%
10%
5%
1%
0%
and V
DO TOP
0.95R
0.99R
0.8R
0.9R
R
R
i1
are extrapolated from the Dropout
1.05R
1.01R
1.2R
1.1R
R
R
i2
DO TOP
OPEAK
100Hz–20kHz
V
-0.500V
-0.250V
-0.125V
-0.025V
02
using Equation 7 and
+ (V
0
- V
(Continued)
01
DO BOT
31.25mA
15.63mA
3.125mA
±
62.5mA
I
)), where
LOAD
1Wrms
0.25dB
1Vrms
0
20kΩ
8Ω
12
Voltage vs Supply Voltage curve in the Typical Perfor-
mance Characteristics section.
Using the Output Power vs Supply Voltage graph for an 8Ω
load, the minimum supply rail just about 5V. Extra supply
voltage creates headroom that allows the LM4927 to repro-
duce peaks in excess of 1W without producing audible dis-
tortion. At this time, the designer must make sure that the
power supply choice along with the output impedance does
not violate the conditions explained in the Power Dissipa-
tion section. Once the power dissipation equations have
been addressed, the required differential gain can be deter-
mined from Equation 8.
From Equation 7, the minimum A
of 2.83 gives R
the bandwidth requirement which must be stated as a single
-3dB frequency point. Five times away from a -3dB point is
0.17dB down from passband response which is better than
the required
The high frequency pole is determined by the product of the
desired frequency pole, f
With a A
150kHz which is much smaller than the LM4927 GBWP of
10MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4927 can still be used without running into bandwidth
limitations.
VD
= 2.83 and f
±
0.25dB specified.
i
= 14kΩ. The final design step is to address
f
H
= 20kHz * 5 = 100kHz
R
H
f
H
/ R
= 100kHz, the resulting GBWP =
, and the differential gain, A
i
= A
VD
VD
is 2.83. A ratio of R
f
to R
VD
(7)
(8)
.
i