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PDF LME49811 Data sheet ( Hoja de datos )
| Número de pieza | LME49811 | |
| Descripción | High Fidelity 200 Volt Power Amplifier Input Stage | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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LME49811
November 11, 2009
www.DataSheet4U.com
Audio Power Amplifier Series
High Fidelity 200 Volt Power Amplifier Input Stage with
Shutdown
General Description
The LME49811 is a high fidelity audio power amplifier input
stage designed for demanding consumer and pro-audio ap-
plications. Amplifier output power may be scaled by changing
the supply voltage and number of output devices. The
LME49811 is capable of driving an output stage to deliver in
excess of 500 watts single-ended into an 8 ohm load in the
presence of 10% high line headroom and 20% supply regu-
lation.
The LME49811 includes thermal shut down circuitry that ac-
tivates when the die temperature exceeds 150°C. The
LME49811's shutdown function when activated, forces the
LME49811 into shutdown state.
Key Specifications
■ Wide operating voltage range
■ PSRR (f = DC)
■ THD+N (f = 1kHz)
■ Output Drive Current
Features
■ Very high voltage operation
■ Scalable output power
■ Minimum external components
■ External compensation
■ Thermal Shutdown
±20V to ±100V
115dB (typ)
0.00035% (typ)
9mA
Applications
■ Powered subwoofers
■ Pro audio
■ Powered studio monitors
■ Audio video receivers
■ Guitar Amplifiers
■ High voltage industrial applications
Typical Application
FIGURE 1. Typical Audio Amplifier Application Circuit
Overture® is a registered trademark of National Semiconductor Corporation.
© 2009 National Semiconductor Corporation 300048
30004862
www.national.com
1 page  
Electrical Characteristics +VCC = –VEE = 100V (Note 1, Note 2)
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The following specifications apply for ISD = 1.5mA, Figure 1, unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LME49811
Typical Limit
Units
(Limits)
(Note 6) (Note 7)
ICC
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
17 22 mA (max)
IEE
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
19 24 mA (max)
THD+N
AV
AV
Total Harmonic Distortion +
Noise
Closed Loop Voltage Gain
Open Loop Gain
No load, AV = 30dB
VOUT = 30VRMS, f = 1kHz
VIN = 1mVRMS, f = 1kHz
f = DC
0.00035
93
120
0.001
26
% (max)
dB (min)
dB
dB
VOM
VNOISE
Output Voltage Swing
Output Noise
THD+N = 0.05%, Freq = 20Hz to 20kHz
LPF = 30kHz, Av = 29dB
A-weighted
68
100
70
VRMS
μV
180 μV (max)
IOUT Output Current
Outputs Shorted
ISD
Current into Shutdown Pin
To put part in “play” mode
9 7 mA(min)
1.5 1 mA(min)
2 mA (max)
SR Slew Rate
VIN = 1.2VP-P, f = 10kHz square Wave,
Outputs shorted
17
14 V/μs (min)
VOS
IB
PSRR
Input Offset Voltage
Input Bias Current
Power Supply Rejection Ratio
VCM = 0V, IO = 0mA
VCM = 0V, IO = 0mA
f = DC, Input Referred
1 3 mV (max)
100 nA (max)
115 105 dB (min)
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability
and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in
the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and the
device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified
Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified
or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed.
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.
Note 4: Human body model, applicable std. JESD22-A114C.
Note 5: Machine model, applicable std. JESD22-A115-A.
Note 6: Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of product
characterization and are not guaranteed.
Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis.
Note 8: The maximum operating junction temperature is 150°C.
Note 9: The Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 30pF, and TA = 25°C except where specified.
5 www.national.com
5 Page 
Application Information
SHUTDOWN FUNCTION
The shutdown function of the LME49811 is controlled by the
amount of current that flows into the shutdown pin. If there is
less than 1mA of current flowing into the shutdown pin, the
part will be in shutdown. This can be achieved by shorting the
shutdown pin to ground or by floating the shutdown pin. If
there is between 1mA and 2mA of current flowing into the
shutdown pin, the part will be in “play” mode. This can be done
by connecting a reference voltage to the shutdown pin
through a resistor (RM). The current into the shutdown pin can
be determined by the equation ISD = (VREF – 2.9) / RM. For
example, if a 5V power supply is connected through a
1.4kΩ resistor to the shutdown pin, then the shutdown current
will be 1.5mA, at the center of the specified range. It is also
possible to use VCC as the power supply for the shutdown pin,
though RM will have to be recalculated accordingly. It is not
recommended to flow more than 2mA of current into the shut-
down pin because damage to the LME49811 may occur.
It is highly recommended to switch between shutdown and
“play” modes rapidly. This is accomplished most easily
through using a toggle switch that alternatively connects the
shutdown pin through a resistor to either ground or the shut-
down pin power supply. Slowly increasing the shutdown cur-
rent may result in undesired voltages on the outputs of the
LME49811, which can damage an attached speaker.
THERMAL PROTECTION
The LME49811 has a thermal protection scheme to prevent
long-term thermal stress of the device. When the temperature
on the die exceeds 150°C, the LME49811 shuts down. It
starts operating again when the die temperature drops to
about 145°C, but if the temperature again begins to rise, shut-
down will occur again above 150°C. Therefore, the device is
allowed to heat up to a relatively high temperature if the fault
condition is temporary, but a sustained fault will cause the
device to cycle in a Schmitt Trigger fashion between the ther-
mal shutdown temperature limits of 150°C and 145°C. This
greatly reduces the stress imposed on the IC by thermal cy-
cling, which in turn improves its reliability under sustained
fault conditions.
Since the die temperature is directly dependent upon the heat
sink used, the heat sink should be chosen so that thermal
shutdown is not activated during normal operation. Using the
best heat sink possible within the cost and space constraints
of the system will improve the long-term reliability of any pow-
er semiconductor device, as discussed in the Determining
the Correct Heat Sink section.
POWER DISSIPATION AND HEAT SINKING
When in “play” mode, the LME49811 draws a constant
amount of current, regardless of the input signal amplitude.
Consequently, the power dissipation is constant for a given
supply voltage and can be computed with the equation
PDMAX = ICC* (VCC– VEE).
DETERMINING THE CORRECT HEAT SINK
The choice of a heat sink for a high-power audio amplifier is
made entirely to keep the die temperature at a level such that
the thermal protection circuitry is not activated under normal
circumstances.
The thermal resistance from the die to the outside air, θJA
(junction to ambient), is a combination of three thermal resis-
tances, θJC (junction to case), θCS (case to sink), and θSA (sink
to ambient). The thermal resistance, θJC (junction to case), of
the LME49811 is 0.4 °C/W. Using Thermalloy Thermacote
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thermal compound, the thermal resistance, θCS (case to sink),
is about 0.2°C/W. Since convection heat flow (power dissi-
pation) is analogous to current flow, thermal resistance is
analogous to electrical resistance, and temperature drops are
analogous to voltage drops, the power dissipation out of the
LME49811 is equal to the following:
PDMAX = (TJMAX−TAMB) / θJA
(1)
where TJMAX = 150°C, TAMB is the system ambient tempera-
ture and θJA = θJC + θCS + θSA.
30004855
Once the maximum package power dissipation has been cal-
culated using equation 1, the maximum thermal resistance,
θSA, (heat sink to ambient) in °C/W for a heat sink can be
calculated. This calculation is made using equation 2 which
is derived by solving for θSA in equation 1.
θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)] / PDMAX
(2)
Again it must be noted that the value of θSA is dependent upon
the system designer's amplifier requirements. If the ambient
temperature that the audio amplifier is to be working under is
higher than 25°C, then the thermal resistance for the heat
sink, given all other things are equal, will need to be smaller.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components is required to meet
the design targets of an application. The choice of external
component values that will affect gain and low frequency re-
sponse are discussed below.
The gain of each amplifier is set by resistors RF and Ri for the
non-inverting configuration shown in Figure 1. The gain is
found by Equation 3 below:
AV = RF / Ri (V/V)
(3)
For best noise performance, lower values of resistors are
used. A value of 1kΩ is commonly used for Ri and then setting
the value of RF for the desired gain. For the LME49811 the
gain should be set no lower than 26dB. Gain settings below
26dB may experience instability.
The combination of Ri with Ci (see Figure 1) creates a high
pass filter. The low frequency response is determined by
these two components. The -3dB point can be found from
Equation 4 shown below:
fi = 1 / (2πRiCi) (Hz)
(4)
If an input coupling capacitor is used to block DC from the
inputs as shown in Figure 5, there will be another high pass
filter created with the combination of CIN and RIN. When using
a input coupling capacitor RIN is needed to set the DC bias
point on the amplifier's input terminal. The resulting -3dB fre-
quency response due to the combination of CIN and RIN can
be found from Equation 5 shown below:
fIN = 1 / (2πRINCIN) (Hz)
(5)
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| PDF Descargar | [ Datasheet LME49811.PDF ] | |
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