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PDF LM4863 Data sheet ( Hoja de datos )
| Número de pieza | LM4863 | |
| Descripción | Dual 2.2W Audio Amplifier Plus Stereo Headphone Function | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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October 1999
LM4863
Dual 2.2W Audio Amplifier Plus Stereo Headphone
Function
General Description
The LM4863 is a dual bridge-connected audio power ampli-
fier which, when connected to a 5V supply, will deliver 2.2W
to a 4Ω load (Note 1) or 2.5W to a 3Ω load (Note 2)with less
than 1.0% THD+N. In addition, the headphone input pin al-
lows the amplifiers to operate in single-ended mode to drive
stereo headphones.
Boomer audio power amplifiers were designed specifically to
provide high quality output power from a surface mount
package while requiring few external components. To sim-
plify audio system design, the LM4863 combines dual bridge
speaker amplifiers and stereo headphone amplifiers on one
chip.
The LM4863 features an externally controlled, low-power
consumption shutdown mode, a stereo headphone amplifier
mode, and thermal shutdown protection. It also utilizes cir-
cuitry to reduce “clicks and pops” during device turn-on.
Note 1: An LM4863MTE which has been properly mounted to the circuit
board will deliver 2.2W into 4Ω. The other package options for the LM4863
will deliver 1.1W into 8Ω. See the Application Information section for
LM4863MTE usage information.
Note 2: An LM4863MTE which has been properly mounted to the circuit
board and forced-air cooled will deliver 2.5W into 3Ω.
Key Specifications
n PO at 1% THD+N
into 3Ω (LM4863MTE)
into 4Ω (LM4863MTE)
into 8Ω (LM4863)
n Single-ended mode - THD+N
at 75mW into 32Ω
n Shutdown current
2.5W(typ)
2.2W(typ)
1.1W(typ)
0.5%(max)
0.7µA(typ)
Features
n Stereo headphone amplifier mode
n “Click and pop” suppression circuitry
n Unity-gain stable
n Thermal shutdown protection circuitry
n Exposed-DAP TSSOP, TSSOP, SOIC and DIP
packaging available
Applications
n Multimedia monitors
n Portable and desktop computers
n Portable televisions
Typical Application
* Refer to the section Proper Selection of External Components, for a detailed discussion of CB size.
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS012881
DS012881-1
www.national.com
1 page  
External Components Description
(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 C i 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.
Typical Performance Characteristics
MTE Specific Characteristics
LM4863MTE
THD+N vs Output Power
LM4863MTE
THD+N vs Frequency
LM4863MTE
THD+N vs Output Power
DS012881-97
LM4863MTE
THD+N vs Frequency
DS012881-99
DS012881-96
LM4863MTE
Power Dissipation vs Power Output
LM4863MTE(Note 16)
Power Derating Curve
DS012881-98
DS012881-90
DS012881-95
Note 16: These curves show the thermal dissipation ability of the LM4863MTE at different ambient temperatures given these conditions:
500LFPM + JEDEC board: The part is soldered to a 1S2P 20-lead exposed-DAP TSSOP test board with 500 linear feet per minute of forced-air flow across
it. Board information - copper dimensions: 74x74mm, copper coverage: 100% (buried layer) and 12% (top/bottom layers), 16 vias under the exposed-DAP.
500LFPM + 2.5in2: The part is soldered to a 2.5in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.
2.5in2: The part is soldered to a 2.5in2, 1oz. copper plane.
Not Attached: The part is not soldered down and is not forced-air cooled.
5 www.national.com
5 Page 
Application Information (Continued)
NO-LOAD DESIGN CONSIDERATIONS
If the outputs of the LM4863 have a load higher than 10kΩ,
the LM4863 may show a small oscillation at high output lev-
els. To prevent this oscillation, place 5kΩ resistors from the
power outputs to ground.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8Ω Bridged Audio Amplifier
Given:
Power Output:
1 Wrms
Load Impedance:
8Ω
Input Level:
1 Vrms
Input Impedance:
20 kΩ
Bandwidth:
100 Hz−20 kHz ± 0.25 dB
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found. A second way to determine the minimum sup-
ply rail is to calculate the required Vopeak using Equation 3
and add the dropout voltage. Using this method, the mini-
mum supply voltage would be (Vopeak + (2 * Vod)), where Vod
is extrapolated from the Dropout Voltage vs Supply Voltage
curve in the Typical Performance Characteristics section.
Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397 µF; use 0.33 µF
The high frequency pole is determined by the product of the
desired high frequency pole, fH, and the differential gain, A
VD. With a AVD = 3 and fH = 100 kHz, the resulting GBWP =
150 kHz which is much smaller than the LM4863 GBWP of
3.5 MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4863 can still be used without running into bandwidth
problems.
DEMOBOARD CIRCUIT LAYOUT
The demoboard circuit layout is provided here as an ex-
ample of a circuit using the LM4863. If an LM4863MTE is
used with this layout, the exposed-DAP is soldered down to
the copper pad beneath the part. Heat is conducted away
from the part by the two large copper pads in the upper cor-
ners of the demoboard.
This demoboard provides enough heat dissipation ability to
allow an LM4863MTE to output 2.2W into 4Ω at 25˚C.
(4)
Using the Output Power vs Supply Voltage graph for an 8Ω
load, the minimum supply rail is 3.9V. But since 5V is a stan-
dard supply voltage in most applications, it is chosen for the
supply rail. Extra supply voltage creates headroom that al-
lows the LM4863 to reproduce peaks in excess of 1W with-
out producing audible distortion. 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 Dissipation section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 4.
All Layers
DS012881-94
(5)
Rf/R i = AVD/2
(6)
From equation 4, the minimum AVD is 2.83; use AVD = 3
Since the desired input impedance was 20 kΩ, and with a
AVD of 3, a ratio of 1.5:1 of Rf to Riresults in an allocation of
Ri = 20 kΩ and R f = 30 kΩ. The final design step is to ad-
dress the bandwidth requirements which must be stated as a
pair of −3 dB frequency points. Five times away from a pole
gives 0.17 dB down from passband response, which is better
than the required ±0.25 dB specified.
fL = 100 Hz/5 = 20 Hz
fH = 20 kHz x 5 = 100 kHz
As stated in the External Components section, Ri in con-
junction with Ci create a highpass filter.
Silk Screen Layer
DS012881-93
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM4863.PDF ] | |
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