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PDF LM4853LD Data sheet ( Hoja de datos )
| Número de pieza | LM4853LD | |
| Descripción | Mono 1.5 W / Stereo 300mW Power Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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January 2003
LM4853
Mono 1.5 W / Stereo 300mW Power Amplifier
General Description
The LM4853 is an audio power amplifier capable of deliver-
ing 1.5W (typ) of continuous average power into a mono 4Ω
bridged-tied load (BTL) with 1% THD+N or 95mW per chan-
nel of continuous average power into stereo 32Ω single-
ended (SE) loads with 1% THD+N, using a 5V power supply.
The LM4853 can automatically switch between mono BTL
and stereo SE modes utilizing a headphone sense pin. It is
ideal for any system that provides both a monaural speaker
output and a stereo line or headphone output
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. Since the LM4853 does not require
bootstrap capacitors or snubber networks, it is optimally
suited for low-power portable systems.
The LM4853 features an externally controlled, micropower
consumption shutdown mode and thermal shutdown protec-
tion. The unity-gain stable LM4853’s gain is set by external
gain-setting resistors
Key Specifications
n Output Power at 1% THD+N, 1kHz:
n LM4853LD 3Ω BTL
n LM4853LD 4Ω BTL
n LM4853MM 4Ω BTL
n LM4853MM,LD 8Ω BTL
n LM4853MM,LD 8Ω SE
n LM4853MM,LD 32Ω SE
n THD+N at 1kHz, 95mW into 32Ω SE
n Single Supply Operation
n Shutdown Current
1.9W (typ)
1.7W (typ)
1.5W (typ)
1.1W (typ)
300mW (typ)
95mW (typ)
1% (typ)
2.4 to 5.5V
18µA (typ)
Features
n Mono 1.5W BTL or stereo 300mW output
n Headphone sense
n “Click and pop” suppression circuitry
n No bootstrap capacitors required
n Thermal shutdown protection
n Unity-gain stable
n Available in space-saving MSOP and LLP packaging
Applications
n Portable computers
n Desktop computers
n PDA’s
n Handheld games
Connection Diagrams
20033429
Top View
10 Lead MSOP
Order Number LM4853MM
See NS Package Number MUB10A
20033428
Top View
14 Lead LLP
Order Number LM4853LD
See NS Package Number LDA14A
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation DS200334
www.national.com
1 page  
External Components Description
See Figure 1.
Components
Functional Description
1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a
high pass filter with Ci at fc = 1/(2πRiCi).
2. Ci Input coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. Also creates a
highpass filter with Ri at fc = 1/(2πRiCi). Refer to the section, Proper Selection of External Components,
for an explanation of how to determine the value of Ci.
3. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri.
4. Cs Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing
section for information concerning proper placement and selection of the supply bypass capacitor.
5. CB Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of
External Components, for information concerning proper placement and selection of CB.
6. CO Output coupling capacitor which blocks the DC voltage at the amplifier’s output. Forms a high pass filter
with the single-ended load RL at fO = 1/(2π RLCO).
Typical Performance Characteristics
LD Specific Characteristics
LM4853LD
THD+N vs Frequency
LM4853LD
THD+N vs Frequency
200334A5
LM4853LD
THD+N vs Output Power
200334A6
LM4853LD
THD+N vs Output Power
200334A7
5
200334A8
www.national.com
5 Page 
Typical Performance Characteristics (Continued)
Power Supply Rejection Ratio
Application Information
BRIDGED AND SINGLE-ENDED OPERATION
As shown in Figure 1, the LM4853 contains three operational
amplifiers (A1-A3). These amplifiers can be configured for
SE or BTL modes.
In the SE mode, the LM4853 operates as a high current
output dual op amp. A1 and A3 are independent amplifiers
with an externally configured gain of AV = - RF/RI. The
outputs of A1 and A3 are used to drive an external set of
headphones plugged into the headphone jack. Amplifier A2
is shut down to a high output impedance state in SE mode.
This prevents any current flow into the mono bridge-tied
load, thereby muting it.
In BTL mode, A3 is shut down to a high impedance state.
The audio signal from the RIGHT IN pin is directed to the
inverting input of A1. As a result, the LEFT IN and RIGHT IN
audio signals, VINL and VINR, are summed together at the
input of A1. A2 is then activated with a closed-loop gain of AV
= -1 fixed by two internal 20kΩ resistors. The outputs of A1
and A2 are then used to drive the mono bridged-tied load.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATION
The LM4853’s exposed-DAP (die attach paddle) package
(LD) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane, and surrounding air. The
result is a low voltage audio power amplifier that produces
1.7W at ≤ 1% THD+N with a 4Ω load. This high power is
achieved through careful consideration of necessary thermal
design. Failing to optimize thermal design may compromise
the LM4853’s high power performance and activate un-
wanted, though necessary, thermal shutdown protection.
The LD package must have its DAP soldered to a copper
pad on the PCB. The DAP’s PCB copper pad is connected to
a large plane of continuous unbroken copper. This plane
forms a thermal mass, heat sink, and radiation area. Place
the heat sink area on either outside plane in the case of a
two-sided PCB, or on an inner layer of a board with more
than two layers. Connect the DAP copper pad to the inner
layer or backside copper heat sink area with 4(2x2) vias. The
20033474
via diameter should be 0.012in-0.013in with a 1.27mm pitch.
Ensure efficient thermal conductivity by plating through the
vias.
Best thermal performance is achieved with the largest prac-
tical heat sink area. If the heatsink and amplifier share the
same PCB layer, a nominal 2.5in2 area is necessary for 5V
operation with a 4Ω load. Heatsink areas not placed on the
same PCB layer as the LM4853 should be 5in2 (min) for the
same supply voltage and load resistance. The last two area
recommendations apply for 25˚C ambient temperature. In-
crease the area to compensate for ambient temperatures
above 25˚C. The LM4853’s power de-rating curve in the
Typical Performance Characteristics shows the maximum
power dissipation versus temperature. An example PCB lay-
out for the LD package is shown in the Demonstration
Board Layout section. Further detailed and specific infor-
mation concerning PCB layout, fabrication, and mounting an
LD (LLP) package is available from National Semiconduc-
tor’s Package Engineering Group under application note
AN1187.
BRIDGE CONFIGURATION EXPLANATION
When the LM4853 is in BTL mode, the output of amplifier A1
serves as the input to amplifier A2, which results in both
amplifiers producing signals identical in magnitude, but out
of phase by 180˚. Consequently, the differential gain for the
mono channel is:
AVD = VOUT / (VINL + VINR) = 2 x (RF / RI)
(1)
Driving a load differentially through the BTL OUT- and BTL
OUT+ outputs is an amplifier configuration commonly re-
ferred to as "bridged mode". Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration. It drives a load differentially,
which doubles output swing for a specified supply voltage.
This produces four times the output power as that produced
by a single-ended amplifier under the same conditions. This
increase in attainable output power assumes that the ampli-
fier is not current limited or clipped. In order to choose an
11 www.national.com
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| PDF Descargar | [ Datasheet LM4853LD.PDF ] | |
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