LM4853MM/NOPB National Semiconductor, LM4853MM/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM4853MM/NOPB
• Description: IC AMP AUDIO PWR 1.9W AB 10MSOP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4853MM/NOPB

• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.9W x 1 @ 3 Ohm; 300mW x 2 @ 8 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Features: Depop, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4853MM; LM4853MMTR

Application Information
Also shown in Figure 2 are the electrical connections for the
headphone jack and plug. A 3-wire plug consists of a Tip,
Ring, and Sleave, where the Tip and Ring are audio signal
conductors and the Sleave is the common ground return.
One control pin for each headphone jack is sufficient to
indicate to the control inputs that a user has inserted a plug
into the jack and that the headphone mode of operation is
desired.
To ensure smooth transition from BTL to SE operation, it is
important to connect HP-IN and R
the Right Output of the headphone jack. The control pin on
the Left Output of the headphone jack should be left open.
Connecting the node between the HP-IN and R
Left Output control pin may cause unwanted state changes
to the HP-IN pin.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical for optimum device
and system performance. While the LM4853 is tolerant to a
variety of external component combinations, consideration
must be given to the external component values that maxi-
mize overall system quality.
The LM4853’s unity-gain stability allows a designer to maxi-
mize system performance. The LM4853’s gain should be set
no higher than necessary for any given application. A low
gain configuration maximizes signal-to-noise performance
and minimizes THD+N. However, a low gain configuration
also requires large input signals to obtain a given output
power. Input signals equal to or greater than 1V
available from sources such as audio codecs. Please refer to
the section, Audio Power Amplifier Design, for a more
complete explanation of proper gain selection.
Selecting Input and Output Capacitor Values
Besides gain, one of the major considerations is the closed-
loop bandwidth of the amplifier. To a large extent, the band-
width is dictated by the choice of external components
shown in Figure 1. The input coupling capacitor C
resistor R
frequency response. C
desired frequency response weighed against the following:
Large value input and output capacitors are both expensive
and space consuming for portable designs. Clearly a certain
FIGURE 2. Headphone Control Circuit
I
form a first order high pass filter that limits low
I
’s value should be based on the
PU1
to the control pin on
(Continued)
20033450
PU1
RMS
to the
I
and
are
13
sized capacitor is needed to couple in low frequencies with-
out severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Thus, large
value input and output capacitors may not increase system
performance.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W / 8Ω Bridged Audio Amplifier
Given:
A designer must first determine the minimum supply voltage
needed to obtain the specified output power. By extrapolat-
ing from the Output Power vs Supply Voltage graphs in the
Typical Performance Characteristics section, the supply
rail can be easily found. A second way to determine the
minimum supply rail is to calculate the required V
using Equation 5 and add the dropout voltage. This results in
Equation 6, where V
from the Dropout Voltage vs Supply Voltage curve in the
Typical Performance Characteristics section.
Using the Output Power vs Supply Voltage graph for an 8Ω
load, the minimum supply rail is 4.7V. But since 5V is a
standard supply voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4853 to reproduce peaks in excess of 1W
without producing audible distortion. However, the designer
must make sure that the chosen power supply voltage and
output load does not violate the conditions explained in the
Power Dissipation section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 7.
From Equation 6, the minimum A
The desired input impedance was 20kΩ, and with an A
3, using Equation 8 results in an allocation of R
R
The final design step is to set the amplifier’s −3dB frequency
bandwidth. To achieve the desired
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 o at least five times
• Power Output:
• Load Impedance
• Input Level:
• Input Impedance:
• Bandwidth:
F
= 30kΩ.
V
DD
≥ (V
OPEAK
R
ODTOP
F
/ R
+ (V
I
= A
and V
ODTOP
VD
VD
100Hz - 20kHz
ODBOT
/ 2
is 2.83; use A
±
+ V
0.25dB pass band
ODBOT
are extrapolated
I
))
= 20kΩ and
www.national.com
±
VD
1W
0.25dB
1V
OPEAK
= 3.
20kΩ
VD
RMS
RMS
8Ω
(5)
(6)
(7)
(8)
of