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PDF LM4918 Data sheet ( Hoja de datos )
| Número de pieza | LM4918 | |
| Descripción | Stereo Audio Amp with AGC Control | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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February 2004
LM4918
Stereo Audio Amp with AGC Control
General Description
The LM4918 is a monolithic integrated circuit that provides a
automatic gain control (AGC), and stereo bridged audio
power amplifiers capable of producing 1W into 8Ω with less
than 1.0% THD.
Boomer® audio integrated circuits were designed specifically
to provide high quality audio while requiring a minimum
amount of external components. The LM4918 incorporates a
AGC and stereo bridged audio power amplifiers making it
optimally suited for multimedia monitors, portable radios,
desktop and portable computer applications.
The LM4918 features an externally controlled, low-power
consumption shutdown mode, and a power amplifier mute
for maximum system flexibility and performance.
Key Specifications
j THD+N at 1kHz, 1W, 8Ω
j Total quiescent power supply current
j Total shutdown power supply current
0.3% (typ)
18mA (typ)
1µA (typ)
Features
n 0.75dB per step/32step AGC Control Interface
n Automatic Gain Control Circuitry
n Stereo Bridged power amplifiers
n “Click and pop” suppression circuitry
n Thermal shutdown protection circuitry
n Selectable Auto Detect Std-by mode and Logic control
Applications
n Portable Computers
n Desktop Computers
n Multimedia monitors
Typical Application
20091301
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation DS200913
www.national.com
1 page  
Typical Performance Characteristics (Note 12)
THD+N vs Frequency
VDD = 3V, RL = 4Ω, BTL, PO = 225mW
THD+N vs Frequency
VDD = 3V, RL = 8Ω, BTL, PO = 275mW
200913F6
THD+N vs Frequency
VDD = 5V, RL = 8Ω, BTL, PO = 400mW
200913F7
THD+N vs Frequency
VDD = 5V, RL = 32Ω, SE, PO = 40mW
200913F8
THD+N vs Frequency
VDD = 3V, RL = 32Ω, SE, PO = 25mW
THD+N vs Output Power
VDD = 3V, RL = 4Ω, BTL
200913H4
200913H5
5
200913F9
www.national.com
5 Page 
Application Information (Continued)
mize thermal design may compromise the LM4918’s perfor-
mance and activate unwanted, though necessary, thermal
shutdown protection.
The LM4918LD must have its DAP soldered to a copper pad
on the PCB. The DAP’s PCB copper pad is then, ideally,
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 or multi-layer PCB. (The heat sink area
can also be placed on an inner layer of a multi-layer board.
The thermal resistance, however, will be higher.) Connect
the DAP copper pad to the inner layer or backside copper
heat sink area with 2 vias. The via diameter should be
0.012in - 0.013in with a 1.27mm pitch. Ensure efficient ther-
mal conductivity by plugging and tenting the vias with plating
and solder mask, respectively. Further detailed and specific
information concerning PCB layout, fabrication, and mount-
ing an LQ (LLP) package is available in National Semicon-
ductor’s AN1187.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
presence does not eliminate the need for a local 1.0µF
tantalum bypass capacitance connected between the
LM4918’s supply pins and ground. Keep the length of leads
and traces that connect capacitors between the LM4918’s
power supply pin and ground as short as possible. Connect-
ing a 2.2µF capacitor, CB, between the BYPASS pin and
ground improves the internal bias voltage’s stability and
improves the amplifier’s PSRR. The PSRR improvements
increase as the bypass pin capacitor value increases. Too
large, however, increases turn-on time and can compromise
the amplifier’s click and pop performance. The selection of
bypass capacitor values, especially CB, depends on desired
PSRR requirements, click and pop performance system
cost, and size constraints.
FIGURE 2. REFERENCE DESIGN BOARD SCHEMATIC
200913I8
11 www.national.com
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet LM4918.PDF ] | |
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