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PDF LM4810MA Data sheet ( Hoja de datos )
| Número de pieza | LM4810MA | |
| Descripción | Dual 105mW Headphone Amplifier with Active-High Shutdown Mode | |
| Fabricantes | National Semiconductor | |
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November 2002
LM4810
Dual 105mW Headphone Amplifier with Active-High
Shutdown Mode
General Description
The LM4810 is a dual audio power amplifier capable of
delivering 105mW per channel of continuous average power
into a 16Ω load with 0.1% (THD+N) from a 5V power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. Since the LM4810 does not require
bootstrap capacitors or snubber networks, it is optimally
suited for low-power portable systems.
The unity-gain stable LM4810 can be configured by external
gain-setting resistors.
The LM4810 features an externally controlled, active-high,
micropower consumption shutdown mode, as well as an
internal thermal shutdown protection mechanism.
Key Specifications
n THD+N at 1kHz, 105mW continuous average power into
16Ω 0.1% (typ)
n THD+N at 1kHz, 70mW continuous average power into
32Ω 0.1% (typ)
n Shutdown Current
0.4µA (typ)
Features
n Active-high shutdown mode
n LLP, MSOP, and SO surface mount packaging
n "Click and Pop" suppression circuitry
n Low shutdown current
n No bootstrap capacitors required
n Unity-gain stable
Applications
n Cellular Phones
n Personal Computers
n Microphone Preamplifier
n PDA’s
Typical Application
20008901
*Refer to the Application Information Section for information concerning proper selection of the input and output coupling capacitors.
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2002 National Semiconductor Corporation DS200089
www.national.com
1 page  
External Components Description (Figure 1)
Components
1. Ri
2. Ci
3. Rf
4. CS
5. CB
6. CO
Functional Description
The inverting input resistance, along with Rf, set the closed-loop gain. Ri, along with Ci, form a high
pass filter with fc = 1/(2πRiCi).
The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. Ci, along with Ri,
create a highpass filter with fc = 1/(2πRiCi). Refer to the section, Selecting Proper External
Components, for an explanation of determining the value of Ci.
The feedback resistance, along with Ri, set closed-loop gain.
This is the supply bypass capacitor. It provides power supply filtering. Refer to the Application
Information section for proper placement and selection of the supply bypass capacitor.
This is the BYPASS pin capacitor. It provides half-supply filtering. Refer to the section, Selecting
Proper External Components, for information concerning proper placement and selection of CB.
This is the output coupling capacitor. It blocks the DC voltage at the amplifier’s output and forms a high
pass filter with RL at fO = 1/(2πRLCO)
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
THD+N vs Frequency
20008985
THD+N vs Frequency
20008964
20008965
5
20008966
www.national.com
5 Page 
Typical Performance Characteristics (Continued)
Open Loop
Frequency Response
Supply Current vs
Supply Voltage
20008938
Application Information
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4810’s shutdown function. Activate micro-power shut-
down by applying a logic high voltage to the SHUTDOWN
pin. The logic threshold is typically VDD/2. When active, the
LM4810’s micro-power shutdown feature turns off the ampli-
fier’s bias circuitry, reducing the supply current. The low
0.4µA typical shutdown current is achieved by applying a
voltage that is as near as VDD as possible to the SHUT-
DOWN pin. A voltage that is less than VDD may increase the
shutdown current.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 100kΩ pull-up resistor between the
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and GND. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to VDD through the pull-up resistor, activat-
ing micro-power shutdown. The switch and resistor guaran-
tee that the SHUTDOWN pin will not float. This prevents
unwanted state changes. In a system with a microprocessor
or a microcontroller, use a digital output to apply the control
voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin
with active circuitry eliminates the pull-up resistor.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATION
The LM4810’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 LD package should have its DAP soldered to a copper
pad on the PCB. The DAP’s PCB copper pad may be con-
nected to a large plane of continuous unbroken copper. This
plane forms a thermal mass, heat sink, and radiation area.
However, since the LM4810 is designed for headphone ap-
plications, connecting a copper plane to the DAP’s PCB
20008944
copper pad is not required. The LM4810’s Power Dissipation
vs Output Power Curve in the Typical Performance Char-
acteristics shows that the maximum power dissipated is just
45mW per amplifier with a 5V power supply and a 32Ω load.
Further detailed and specific information concerning PCB
layout, fabrication, and mounting an LD (LLP) package is
available from National Semiconductor’s Package Engineer-
ing Group under application note AN1187.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation 1 states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.
PDMAX = (VDD) 2 / (2π2RL)
(1)
Since the LM4810 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. Even
with the large internal power dissipation, the LM4810 does
not require heat sinking over a large range of ambient tem-
perature. From Equation 1, assuming a 5V power supply and
a 32Ω load, the maximum power dissipation point is 40mW
per amplifier. Thus the maximum package dissipation point
is 80mW. The maximum power dissipation point obtained
must not be greater than the power dissipation that results
from Equation 2:
PDMAX = (TJMAX − TA) / θJA
(2)
For package MUA08A, θJA = 210˚C/W. TJMAX = 150˚C for
the LM4810. Depending on the ambient temperature, TA, of
the system surroundings, Equation 2 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 1 is greater than that of
Equation 2, then either the supply voltage must be de-
11 www.national.com
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