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PDF LM4673 Data sheet ( Hoja de datos )
| Número de pieza | LM4673 | |
| Descripción | Class D Audio Power Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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www.DataSheet4U.com
December 2005
LM4673
Filterless, 2.65W, Mono, Class D Audio Power Amplifier
General Description
The LM4673 is a single supply, high efficiency, 2.65W, mono,
Class D audio amplifier. A low noise, filterless PWM archi-
tecture eliminates the output filter, reducing external compo-
nent count, board area consumption, system cost, and sim-
plifying design.
The LM4673 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing on a single 5V supply, it is capable of driving a 4Ω
speaker load at a continuous average output of 2.1W with
less than 1% THD+N. Its flexible power supply requirements
allow operation from 2.4V to 5.5V.
The LM4673 has high efficiency with speaker loads com-
pared to a typical Class AB amplifier. With a 3.6V supply
driving an 8Ω speaker, the IC’s efficiency for a 100mW
power level is 80%, reaching 88% at 400mW output power.
The LM4673 features a low-power consumption shutdown
mode. Shutdown may be enabled by driving the Shutdown
pin to a logic low (GND).
The gain of the LM4673 is externally configurable which
allows independent gain control from multiple sources by
summing the signals. Output short circuit and thermal over-
load protection prevent the device from damage during fault
conditions.
Key Specifications
j Efficiency at 3.6V, 400mW into 8Ω speaker 88% (typ)
j Efficiency at 3.6V, 100mW into 8Ω speaker 80% (typ)
j Efficiency at 5V, 1W into 8Ω speaker
86% (typ)
j Quiescent current, 3.6V supply
2.1mA (typ)
j Total shutdown power supply current 0.01µA (typ)
j Single supply range
2.4V to 5.5V
j PSRR, f = 217Hz
78dB
Features
n Mono Class D Operation
n No output filter required for inductive loads
n Externally configurable gain
n Very fast turn on time: 17µs (typ)
n Minimum external components
n "Click and pop" suppression circuitry
n Micro-power shutdown mode
n Available in space-saving 0.4mm pitch micro SMD and
LLPTm (Future Product) packages
Applications
n Mobile phones
n PDAs
n Portable electronic devices
Typical Application
201522J3
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation DS201522
www.national.com
1 page  
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature TA. The maximum
allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4673, TJMAX = 150˚C.
The typical θJA is 99.1˚C/W for the micro SMD package.
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 5: Machine Model, 220pF – 240pF discharged through all pins.
Note 6: Typical specifications are specified at 25˚C and represent the parametric norm.
Note 7: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 9: Shutdown current is measured in a normal room environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. The Shutdown pin should
be driven as close as possible to GND for minimal shutdown current and to VDD for the best THD performance in PLAY mode. See the Application Information
section under SHUTDOWN FUNCTION for more information.
Note 10: The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series with the LC filter on the demo
board.
External Components Description
(Figure 1)
Components
1. CS
2. CI
Functional Description
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.
Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals.
5 www.national.com
5 Page 
Application Information (Continued)
pin is floating. The LM4673 will enter the shutdown state
when the Shutdown pin is left floating or if not floating, when
the shutdown voltage has crossed the threshold. To mini-
mize the supply current while in the shutdown state, the
Shutdown pin should be driven to GND or left floating. If the
Shutdown pin is not driven to GND, the amount of additional
resistor current due to the internal shutdown resistor can be
found by Equation (1) below.
(VSD - GND) / 300kΩ
(1)
With only a 0.5V difference, an additional 1.7µA of current
will be drawn while in the shutdown state.
PROPER SELECTION OF EXTERNAL COMPONENTS
The gain of the LM4673 is set by the external resistors, Ri in
Figure 1, The Gain is given by Equation (2) below. Best
THD+N performance is achieved with a gain of 2V/V (6dB).
AV = 2 * 150 kΩ / Ri (V/V)
(2)
It is recommended that resistors with 1% tolerance or better
be used to set the gain of the LM4673. The Ri resistors
should be placed close to the input pins of the LM4673.
Keeping the input traces close to each other and of the same
length in a high noise environment will aid in noise rejection
due to the good CMRR of the LM4673. Noise coupled onto
input traces which are physically close to each other will be
common mode and easily rejected by the LM4673.
Input capacitors may be needed for some applications or
when the source is single-ended (see Figures 3, 5). Input
capacitors are needed to block any DC voltage at the source
so that the DC voltage seen between the input terminals of
the LM4673 is 0V. Input capacitors create a high-pass filter
with the input resistors, Ri. The –3dB point of the high-pass
filter is found using Equation (3) below.
fC = 1 / (2πRi Ci ) (Hz)
(3)
The input capacitors may also be used to remove low audio
frequencies. Small speakers cannot reproduce low bass
frequencies so filtering may be desired . When the LM4673
is using a single-ended source, power supply noise on the
ground is seen as an input signal by the +IN input pin that is
capacitor coupled to ground (See Figures 5 – 7). Setting the
high-pass filter point above the power supply noise frequen-
cies, 217Hz in a GSM phone, for example, will filter out this
noise so it is not amplified and heard on the output. Capaci-
tors with a tolerance of 10% or better are recommended for
impedance matching.
DIFFERENTIAL CIRCUIT CONFIGURATIONS
The LM4673 can be used in many different circuit configu-
rations. The simplest and best performing is the DC coupled,
differential input configuration shown in Figure 2. Equation
(2) above is used to determine the value of the Ri resistors
for a desired gain.
Input capacitors can be used in a differential configuration as
shown in Figure 3. Equation (3) above is used to determine
the value of the Ci capacitors for a desired frequency re-
sponse due to the high-pass filter created by Ci and Ri.
Equation (2) above is used to determine the value of the Ri
resistors for a desired gain.
The LM4673 can be used to amplify more than one audio
source. Figure 4 shows a dual differential input configuration.
The gain for each input can be independently set for maxi-
mum design flexibility using the Ri resistors for each input
and Equation (2). Input capacitors can be used with one or
more sources as well to have different frequency responses
depending on the source or if a DC voltage needs to be
blocked from a source.
SINGLE-ENDED CIRCUIT CONFIGURATIONS
The LM4673 can also be used with single-ended sources but
input capacitors will be needed to block any DC at the input
terminals. Figure 5 shows the typical single-ended applica-
tion configuration. The equations for Gain, Equation (2), and
frequency response, Equation (3), hold for the single-ended
configuration as shown in Figure 5.
When using more than one single-ended source as shown in
Figure 6, the impedance seen from each input terminal
should be equal. To find the correct values for Ci3 and Ri3
connected to the +IN input pin the equivalent impedance of
all the single-ended sources are calculated. The single-
ended sources are in parallel to each other. The equivalent
capacitor and resistor, Ci3 and Ri3, are found by calculating
the parallel combination of all Civalues and then all Ri val-
ues. Equations (4) and (5) below are for any number of
single-ended sources.
Ci3 = Ci1 + Ci2 + Cin ... (F)
(4)
Ri3 = 1 / (1/Ri1 + 1/Ri2 + 1/Rin ...) (Ω)
(5)
The LM4673 may also use a combination of single-ended
and differential sources. A typical application with one single-
ended source and one differential source is shown in Figure
7. Using the principle of superposition, the external compo-
nent values can be determined with the above equations
corresponding to the configuration.
11 www.national.com
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LM4673.PDF ] | |
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