|
|
PDF LM4840LQ Data sheet ( Hoja de datos )
| Número de pieza | LM4840LQ | |
| Descripción | Stereo 2W Audio Power Amplifiers with Digital Volume Control and Input Mux | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM4840LQ (archivo pdf) en la parte inferior de esta página. Total 19 Páginas | ||
|
No Preview Available !
December 2001
LM4840
Stereo 2W Audio Power Amplifiers
with Digital Volume Control and Input Mux
General Description
The LM4840 is a monolithic integrated circuit that provides
digital volume control and stereo bridged audio power am-
plifiers capable of producing 2W into 4Ω (Note 1) with less
than 1.0% THD or 2.2W into 3Ω (Note 2) 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 LM4840 incorporates a
digital volume control, stereo bridged audio power amplifiers,
an input mux, and a last volume level memory function to
save the volume setting during shutdown. These features
make it optimally suited for multimedia monitors, portable
radios, desktop, and portable computer applications.
The LM4840 features an externally controlled, low-power
consumption shutdown mode, and both a power amplifier
and headphone mute for maximum system flexibility and
performance.
Note 1: When properly mounted to the circuit board, the LM4840LQ and
LM4840MH will deliver 2W into 4Ω. The LM4840MT will deliver 1.1W into 8Ω.
See the Application Information section LM4840LQ and for LM4840MH us-
age information.
Note 2: An LM4840LQ and LM4840MH that have been properly mounted to
the circuit board and forced-air cooled will deliver 2.2W into 3Ω.
Key Specifications
n PO at 1% THD+N
n into 3Ω (LM4840LQ, LM4840MH)
2.2W (typ)
n into 4Ω (LM4840LQ, LM4840MH)
2.0W (typ)
n into 8Ω (LM4840)
1.1W (typ)
n Single-ended mode - THD+N at 85mW into 32Ω 1.0%
(typ)
n Shutdown current
0.2µA (typ)
Features
n PC98 and PC99 Compliant
n Digital Volume Control Interface
n System Beep Detect
n Stereo switchable bridged/single-ended power amplifiers
n “Click and pop” suppression circuitry
n Thermal shutdown protection circuitry
n Input Mux
n Capless headphone drivers
n Last volume memory from shutdown
Applications
n Portable and Desktop Computers
n Multimedia Monitors
n Portable Radios, PDAs, and Portable TVs
Connection Diagram
LLP Package
DS200104-35
Top View
Order Number LM4840LQ
See NS Package Number LQA028A for Exposed-DAP LLP
Boomer® is a registered trademark of NationalSemiconductor Corporation.
© 2001 National Semiconductor Corporation DS200104
www.national.com
1 page  
MH and LQ Specific Characteristics
LM4840MH, LM4840LQ
THD+N vs Output Power
LM4840MH, LM4840LQ
THD+N vs Frequency
LM4840MH, LM4840LQ
THD+N vs Output Power
DS200104-70
LM4840MH, LM4840LQ
THD+N vs Frequency
DS200104-71
DS200104-72
LM4840MH, LM4840LQ
Power Dissipation vs Output Power
LM4840MH(Note 17)
Power Derating Curve
DS200104-73
DS200104-65
Note 17: These curves show the thermal dissipation ability of the LM4840MH at different ambient temperatures given these conditions:
500LFPM + 2in2: The part is soldered to a 2in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it.
2in2on bottom: The part is soldered to a 2in2, 1oz. copper plane that is on the bottom side of the PC board through 21 8 mil vias.
2in2: The part is soldered to a 2in2, 1oz. copper plane.
1in2: The part is soldered to a 1in2, 1oz. copper plane.
Not Attached: The part is not soldered down and is not forced-air cooled.
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
THD+N vs Frequency
DS200104-64
DS200104-57
DS200104-58
5
DS200104-14
www.national.com
5 Page 
Application Information (Continued)
level without forced air cooling. In all circumstances and
conditions, the junction temperature must be held below
150˚C to prevent activating the LM4840’s thermal shutdown
protection. The LM4840’s power derating curve in the Typi-
cal Performance Characteristics shows the maximum
power dissipation versus temperature. Further detailed and
specific information concerning PCB layout, fabrication, and
mounting an LQ (LLP) package is available in National
Semiconductor’s 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 load.
PDMAX = (VDD)2/(2π 2RL) (1)
However, a direct consequence of the increased power de-
livered to the load by a bridged amplifier is an increase in
internal power dissipation. Equation 2 states the maximum
power dissipation point for a bridged amplifier operating at a
given supply voltage and driving a specified load.
PDMAX = 4(VDD)2/(2π 2RL) (2)
Since theLM4840 is a stereo power amplifier, the maximum
internal power dissipation is two times that of Equation 1 or
Equation 2 depending on the mode of operation. Even with
the power dissipation of the stereo amplifiers, the LM4840
does not require heatsinking. The power dissipation from the
amplifiers, must not be greater than the package power
dissipation that results from Equation 3:
PDMAX = (TJMAX − TA)/ θ JA (3)
For the LM4840 TSSOP package, θJA = 80˚C/W and TJMAX
= 150˚C. Depending on the ambient temperature, T A, of the
system surroundings, Equation 3 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 1 and 2 is greater than
that of Equation 3, then either the supply voltage must be
decreased, the load impedance increased, or the ambient
temperature reduced. For the typical application of a 5V
power supply, with an 8Ω bridged loads, the maximum am-
bient temperature possible without violating the maximum
junction temperature is approximately 48˚C provided that
device operation is around the maximum power dissipation
points. Power dissipation is a function of output power and
thus, if typical operation is not around the maximum power
dissipation point, the ambient temperature can be increased.
Refer to the Typical Performance Characteristics curves
for power dissipation information for different output powers.
LAYOUT
As stated in the Grounding section, placement of ground
return lines is imperative in maintaining the highest level of
system performance. It is not only important to route the
correct ground return lines together, but also to be aware of
where the ground return lines are routed with respect to each
other. The output load ground returns should be physically
located as far as possible from low signal level lines and their
ground return lines.
3Ω and 4Ω Layout Considerations
With low impedance loads, the output power at the loads is
heavily dependent on trace resistance from the output pins
of the LM4840. Traces from the output of the LM4840MH to
the load or load connectors should be as wide as practical.
Any resistance in the output traces will reduce the power
delivered to the load. For example, with a 4Ω load and 0.1Ω
of trace resistance in each output, output power at the load
drops from 2W to 1.8W.
Output power is also dependent on supply regulation. To
keep the supply voltage from sagging under full output con-
ditions, the supply traces should be as wide as practical.
Grounding
In order to achieve the best possible performance, there are
certain grounding techniques to be followed. All input refer-
ence grounds should be tied with their respective source
grounds and brought back to the power supply ground sepa-
rately from the output load ground returns. Bringing the
ground returns for the output loads back to the supply sepa-
rately will keep large signal currents from interfering with the
stable AC input ground references. The exposed-DAP of the
LM4840MH package must be tied to ground.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. The effect of a larger half supply bypass capacitor
is improved PSRR due to increased half-supply stability.
Typical applications employ a 5 volt regulator with 10 µF and
a 0.1 µF bypass capacitors which aid in supply stability, but
do not eliminate the need for bypassing the supply nodes of
the LM4840. The selection of bypass capacitors, especially
C B, is thus dependant upon desired PSRR requirements,
click and pop performance as explained in the section,
Proper Selection of External Components, system cost,
and size constraints. It is also recommended to decouple
each of the VDD pins with a 0.1µF capacitor to ground.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4840 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
The LM4840’s bridged amplifier should be used in low gain
configurations to minimize THD+N values, and maximize the
signal to noise ratio. Low gain configurations require large
input signals to obtain a given output power. Input signals
equal to or greater than 1Vrms are available from sources
such as audio codecs.
Besides gain, one of the major considerations is the closed-
loop bandwidth of the amplifier. To a large extent, the band-
width is dictated by the choice of external components. Both
the input coupling capacitor, CI, and the output coupling
capacitor form first order high pass filters which limit low
frequency response given in Equations 4 and 5.
fIC = 1/(2πRiCi) (4)
fOC = 1/(2πRLCO) (5)
These values should be chosen based on required fre-
quency response.
Selection of Input and Output Capacitor Size
Large input and output capacitors are both expensive and
space hungry for portable designs. Clearly, a certain sized
capacitor is needed to couple in low frequencies without
11 www.national.com
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet LM4840LQ.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM4840LQ | Stereo 2W Audio Power Amplifiers with Digital Volume Control and Input Mux | National Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |