NSC LME49810 200v audio power amplifier driver with baker clamp Datasheet

LME49810
200V Audio Power Amplifier Driver with Baker Clamp
General Description
Key Specifications
The LME49810 is a high fidelity audio power amplifier driver
designed for demanding consumer and pro-audio applications. Amplifier output power may be scaled by changing the
supply voltage and number of power transistors. The
LME49810’s minimum output current is 50mA. When using a
discrete output stage the LME49810 is capable of delivering
in excess of 300 watts into a single-ended 8Ω load.
Unique to the LME49810 is an internal Baker Clamp. This
clamp insures that the amplifier output does not saturate
when over driven. The resultant “soft clipping” of high level
audio signals suppresses undesirable audio artifacts generated when conventional solid state amplifiers are driven hard
into clipping.
The LME49810 includes thermal shutdown circuitry that activates when the die temperature exceeds 150°C. The
LME49810’s mute function, when activated, mutes the input
drive signal and forces the amplifier output to a quiescent
state.
■ Wide operating voltage range
■ Slew Rate
±20V to ±100V
50V/μs (typ)
■ Output Drive Current
60mA (typ)
■ PSRR (f = DC)
110dB (typ)
■ THD+N (f = 1kHz)
0.0007 (typ)
Features
■
■
■
■
■
Very high voltage operation
Output clamp logic output
Thermal shutdown and mute
Customizable external compensation
Scalable output power
Applications
■
■
■
■
■
■
Guitar amplifiers
Powered studio monitors
Powered subwoofers
Pro audio
Audio video receivers
High voltage industrial applications
Boomer® is a registered trademark of National Semiconductor Corporation.
Tru-GND is a trademark of National Semiconductor Corporation.
© 2007 National Semiconductor Corporation
202167
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LME49810 200V Audio Power Amplifier Driver with Baker Clamp
September 2007
LME49810
Typical Application
20216772
FIGURE 1. LME49810 Audio Amplifier Schematic
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LME49810
Connection Diagram
TB Package
20216702
Top View
Order Number LME49810TB
See NS Package Number TB15A
N = National Logo
U = Fabrication plant code
Z = Assembly plant code
XY = 2 Digit date code
TT = Die traceability
TB = Package code
Pin Descriptions
Pin
Pin Name
1
ClpFlag
Description
2
Mute
Mute Control
3
GND
Device Ground
4
IN+
Non-Inverting Input
5
IN–
Inverting Input
6
Comp
External Compensation Connection
7
NC
No Connect, Pin electrically isolated
8
Osense
Baker Clamp Clip Flag Output
Output Sense
9
NC
10
–VEE
No Connect, Pin electrically isolated
Negative Power Supply
11
BiasM
Negative External Bias Control
12
BiasP
Positive External Bias Control
13
Sink
Output Sink
14
Source
15
+VCC
Output Source
Positive Power Supply
3
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LME49810
20216708
FIGURE 2. LME49810 Simplified Schematic
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If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage |V+| + |V-|
Differential Input Voltage
Common Mode Input Range
Power Dissipation (Note 3)
ESD Susceptibility (Note 4)
ESD Susceptibility (Note 5)
Junction Temperature (TJMAX) (Note 9)
Soldering Information
200V
±6V
0.4VEE to 0.4VCC
4W
1kV
200V
150°C
260°C
–40°C to +150°C
θJA
73°C/W
θJC
4°C/W
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage
Electrical Characteristics VCC = +100V, VEE = –100V
−40°C ≤ TA ≤ +8 5°C
±20V ≤ VSUPPLY ≤ ±100V
(Notes 1, 2)
The following specifications apply for IMUTE = 100μA, unless otherwise specified. Limits apply for TA = 25°C, CC = 10pF, and AV =
29dB.
LME49810
Symbol
Parameter
Conditions
Typical
(Note 6)
Limits
(Notes 7, 8)
18
Units
(Limits)
ICC
Quiescent Power Supply Current
VCM = 0V, VO = 0V, IO = 0A
11
IEE
Quiescent Power Supply Current
VCM = 0V, VO = 0V, IO = 0A
13
mA (max)
THD+N
No Load, BW = 30kHz
Total Harmonic Distortion + Noise
VOUT = 30VRMS, f = 1kHz
0.0007
% (max)
AV
Open Loop Gain
f = DC
f = 1kHz, VIN = 1mVRMS
120
88
dB
dB
VOM
Output Voltage Swing
THD+N = 0.05%, f = 1kHz
67.5
V RMS
VNOISE
Output Noise
BW = 30kHz,
A-weighted
50
34
150
μV
μV (max)
IOUT
Output Current
Current from Source to Sink Pins
60
50
mA (min)
IMUTE
Current into Mute Pin
To activate the amplifier
100
50
200
μA (min)
μA (max)
SR
Slew Rate
VIN = 1VP-P,
f = 10kHz square Wave
50
VOS
Input Offset Voltage
VCM = 0V, IO= 0mA
1
3
mV (max)
IB
Input Bias Current
VCM = 0V, IO= 0mA
100
200
nA (max)
PSRR
Power Supply Rejection Ratio
f = DC, Input Referred
110
105
dB (min)
VCLIP
Baker Clamp Clipping Voltage
Clip Output
Source pin
Sink pin
97.2
–96.4
95.5
–95.5
V (max)
V (min)
VBC
Baker Clamp Flag Output Voltage IFLAG = 4.7mA
VBA
Bias P&M Pin Open Voltage
IBIAS
Bias Adjust Function Current
0.4
BiasP - BiasM
5
mA (max)
V/μs(min)
V
10
V
2.8
mA
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LME49810
T Package (10 seconds)
Storage Temperature
Thermal Resistance
Absolute Maximum Ratings (Notes 1, 2)
LME49810
Note 1: All voltages are measured with respect to the GND 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, θJC, and the ambient temperature, TA. The maximum
allowable power dissipation is PDMAX = (TJMAX - TA) / θJC or the number given in Absolute Maximum Ratings, whichever is lower. For the LME49810, TJMAX = 150°
C and the typical θJC is 4°C/W. Refer to the Thermal Considerations section for more information.
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 5: Machine Model, 220pF - 240pF discharged through all pins.
Note 6: Typicals are measured at +25°C and represent the parametric norm.
Note 7: 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: The maximum operating junction temperature is 150°C.
Note 10: Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 10pF, and TA = 25°C except where specified.
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LME49810
20216709
FIGURE 3. LME49810 Test Circuit Schematic (DC Coupled)
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LME49810
Typical Performance Characteristics
(Note 10)
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 5V
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 10V
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20216745
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 14V
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 20V
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20216747
THD+N vs Frequency
+VCC = –VEE = 100V, VO = 14V
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 30V
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LME49810
THD+N vs Output Voltage
+VCC = – VEE = 50V, f = 20Hz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20Hz
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THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 1kHz
THD+N vs Output Voltage
+VCC = – VEE = 100V, f = 1kHz
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20216754
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 20kHz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20kHz
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20216758
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LME49810
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20Hz
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 1kHz
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THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20kHz
Closed Loop Frequency Response
+VCC = –VEE = 50V, VIN = 1VRMS
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Closed Loop Frequency Response
+VCC = –VEE = 100V, VIN = 1VRMS
PSRR vs Frequency
+VCC = –VEE = 100V,
No Filters, Input referred, VRIPPLE = 1VRMS on VCC pin
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20216726
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LME49810
PSRR vs Frequency
+VCC = –VEE = 100V,
No Filters, Input referred, VRIPPLE = 1VRMS on VEE pin
Mute Attenuation vs IMUTE
+VCC = –VEE = 100V
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Output Voltage vs Supply Voltage
Slew Rate vs Compensation Capacitor
+VCC = –VEE = 100V, VIN = 1.2VP 10kHz squarewave
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Supply Current vs Supply Voltage
Input Offset Voltage vs Supply Voltage
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20216741
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LME49810
Open Loop Gain and Phase Margin
+VCC = –VEE = 100V
CMRR vs Frequency
+VCC = –VEE = 100V
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Noise Floor
+VCC = –VEE = 50V, VIN = 0V
Noise Floor
+VCC = –VEE = 100V, VIN = 0V
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Baker Clamp Flag Output
+VCC = –VEE = 100V, VIN = 4VRMS, fIN = 20kHz
Ch1: Output, Ch2: CLPFLAG Output
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reference voltage is not available, the following circuit using
a Zener diode can be used to power the CLPFLAG pin from
the higher supply voltage rails of the LME49810. The power
dissipation rating of RZ will need to be at-least ½W if using a
5V Zener Diode. Alternately, the following basic formula can
be used to find the proper power rating of RZ : PDZ = (VCC VZ)2/RZ (W). This formula can also be used to meet the design
requirements of any other reference voltage that the user desires.
MUTE FUNCTION
The mute function of the LME49810 is controlled by the
amount of current that flows into the MUTE pin. LME49810
typically requires 50μA to 100μA of mute current flowing in
order to be in “play” mode. This can be done by connecting a
reference voltage (VMUTE) to the MUTE pin through a resistor
(RM). The following formula can be used to calculate the mute
current.
IMUTE = (VMUTE-0.7V) / (RM+10kΩ) (A)
(1)
The 10kΩ resistor value in Equation 1 is internal. Please refer
to Figure 2, LME49810 Simplified Schematic, for additional
details. For example, if a 5V voltage is connected through a
33kΩ resistor to the MUTE pin, then the mute current will be
100μA, according to Equation 1. Consequently, RM can be
changed to suit any other reference voltage requirement. The
LME49810 will enter Mute mode if IMUTE is less than 1μA
which can be accomplished by shorting the MUTE pin to
ground or by floating the MUTE pin. It is not recommended
that more than 200μA flow into the MUTE pin because damage to LME49810 may occur and device may not function
properly.
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THERMAL PROTECTION
The LME49810 has a thermal protection scheme to prevent
long-term thermal stress of the device. When the temperature
on the die exceeds 150°C, the LME49810 goes into thermal
shutdown. The LME49810 starts operating again when the
die temperature drops to about 145°C, but if the temperature
again begins to rise, shutdown 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 between the thermal shutdown temperature limits of 150°C and 145°C. This greatly
reduces the stress imposed on the IC by thermal cycling,
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 power semiconductor device, as discussed in the Determining the Correct Heat Sink section.
BAKER CLAMP AND CLAMP FLAG OUTPUT
The LME49810 features a Baker Clamp function with corresponding CLPFLAG output pin. The clamp function keeps all
transistors in linear operation when the output goes into clipping. In addition, when the output goes into clipping, a logic
low level appears at the CLPFLAG pin. The CLPFLGAG pin
can be used to drive an LED or some other visual display as
shown by Figure 1. The value of logic low voltage varies and
depends on IFLAG. For example, if IFLAG is 4.7mA then a voltage (VBC) of 0.4V will appear at the CLPFLAG output pin. The
smooth response of the Baker Clamp and the corresponding
CLPFLAG logic output is shown in the scope photo below:
POWER DISSIPATION
When in “play” mode, the LME49810 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). For a quick calculation of PDMAX,
approximate the current to be 11mA and multiply it by the total
supply voltage (the current varies slightly from this value over
the operating range).
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 resistances, θJC (junction to case), θCS (case to sink), and θSA (sink
to ambient). The thermal resistance, θJC (junction to case), of
the LME49810 is 4°C/W. Using Thermalloy Thermacote thermal compound, the thermal resistance, θCS (case to sink), is
about 0.2°C/W. Since convection heat flow (power dissipation) is analogous to current flow, thermal resistance is analogous to electrical resistance, and temperature drops are
20216740
+VCC = -VEE = 100V, VIN = 4VRMS, fIN = 1kHz, RC = 1kΩ
Ch1: Output, Ch2: CLPFLAG Output
The CLPFLAG pin can source up to 10mA, and since the
CLPFLAG output is an open collector output as shown by
Figure 2, LME49810 Simplified Schematic, it should never be
left to float under normal operation. If CLPFLAG pin is not
used, then it should be connected through a resistor to a reference voltage so that IFLAG is below 10mA. For example, a
resistor of 1k can be used with a 5V reference voltage. This
will give the IFLAG of 4.7mA. In a typical LED setup, if +5V
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LME49810
Application Information
LME49810
is an electrolytic type. An additional small value, high quality
film capacitor may be used in parallel with the feedback resistor to improve high frequency sonic performance. If DC
offset in the output stage is acceptable without the feedback
capacitor, it may be removed but DC gain will now be equal
to AC gain.
analogous to voltage drops, the power dissipation out of the
LME49810 is equal to the following:
PDMAX = (TJMAX−TAMB) / θJA
(2)
where TJMAX = 150°C, TAMB is the system ambient temperature and θJA = θJC + θCS + θSA.
COMPENSATION CAPACITOR
The compensation capacitor (CC) is one of the most critical
external components in value, placement and type. The capacitor should be placed close to the LME49810 and a silver
mica type will give good performance. The value of the capacitor will affect slew rate and stability. The highest slew rate
is possible while also maintaining stability through out the
power and frequency range of operation results in the best
audio performance. The value shown in Figure 1 should be
considered a starting value with optimization done on the
bench and in listening testing. Please refer to Slew Rate vs.
CC Graph in Typical Performance Characteristics for determining the proper slew rate for your particular application.
20216771
Once the maximum package power dissipation has been calculated using Equation 2, 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 3 which
is derived by solving for θSA from Equation 2.
θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)] / PDMAX
SUPPLY BYPASSING
The LME49810 has excellent power supply rejection and
does not require a regulated supply. However, to eliminate
possible oscillations all op amps and power op amps should
have their supply leads bypassed with low-inductance capacitors having short leads and located close to the package
terminals. Inadequate power supply bypassing will manifest
itself by a low frequency oscillation known as “motorboating”
or by high frequency instabilities. These instabilities can be
eliminated through multiple bypassing utilizing a large electrolytic capacitor (10μF or larger) which is used to absorb low
frequency variations and a small ceramic capacitor (0.1μF) to
prevent any high frequency feedback through the power supply lines. If adequate bypassing is not provided the current in
the supply leads which is a rectified component of the load
current may be fed back into internal circuitry. This signal
causes low distortion at high frequencies requiring that the
supplies be bypassed at the package terminals with an electrolytic capacitor of 470μF or more.
(3)
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 response are discussed below.
The overall gain of the amplifier is set by resistors RF and Ri
for the non-inverting configuration shown in Figure 1. The gain
is found by Equation 4 below given Ri = RIN and RF = RS.
AV = RF / Ri (V/V)
(4)
OUTPUT STAGE USING BIPOLAR TRANSISTORS
With a properly designed output stage and supply voltage of
±100V, an output power up to 500W can be generated at
0.05% THD+N into an 8Ω speaker load. With an output current of several amperes, the output transistors need substantial base current drive because power transistors usually have
quite low current gain—typical hfe of 50 or so. To increase the
current gain, audio amplifiers commonly use Darlington style
devices. Power transistors should be mounted together with
the VBE multiplier transistor on the same heat sink to avoid
thermal run away. Please see the section Biasing Technique and Avoiding Thermal Runaway for additional information.
For best Noise performance, lower values of resistors are
used. A value of 243 is commonly used for Ri and setting the
value for RF for desired gain. For the LME49810 the gain
should be set no lower than 10V/V. Gain settings below 10V/
V may experience instability.
The combination of Ri and Ci (see Figure 1) creates a high
pass filter. The gain at low frequency and therefore the response is determined by these components. The -3dB point
can be determined from Equation 5 shown below:
fi = 1 / (2πRiCi) (Hz)
(5)
BIASING TECHNIQUES AND AVOIDING THERMAL
RUNAWAY
A class AB amplifier has some amount of distortion called
Crossover distortion. To effectively minimize the crossover
distortion from the output, a VBE multiplier may be used instead of two biasing diodes. The LME49810 has two dedicated pins (BIASM and BIASP) for Bias setup and provide a
constant current source of about 2.8mA. A VBE multiplier normally consists of a bipolar transistor (QMULT, see Figure 1) and
two resistors (RB1 and RB2, see Figure 1). A trim pot can also
be added in series with RB1 for optional bias adjustment. A
properly designed output stage, combine with a VBE multiplier,
If an input coupling capacitor (CIN) is used to block DC from
the inputs as shown in Figure 1, there will be another high
pass filter created with the combination of CIN and RIN. The
resulting -3dB frequency response due to the combination of
CIN and RIN can be found from equation 6 shown below:
fIN = 1 / (2πRINCIN) (Hz)
(6)
For best audio performance, the input capacitor should not be
used. Without the input capacitor, any DC bias from the
source will be transferred to the load. The feedback capacitor
(Ci) is used to set the gain at DC to unity. Because a large
value is required for a low frequency -3dB point, the capacitor
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VBIAS = VBE(1+RB2/RB1) (V)
LAYOUT CONSIDERATION AND AVOIDING GROUND
LOOPS
A proper layout is virtually essential for a high performance
audio amplifier. It is very important to return the load ground,
supply grounds of output transistors, and the low level (feedback and input) grounds to the circuit board common ground
point through separate paths. When ground is routed in this
fashion, it is called a star ground or a single point ground. It
is advisable to keep the supply decoupling capacitors of
0.1μF close as possible to LME49810 to reduce the effects of
PCB trace resistance and inductance. Following the general
rules will optimize the PCB layout and avoid ground loops
problems:
a) Make use of symmetrical placement of components.
b) Make high current traces, such as output path traces, as
wide as possible to accomodate output stage current requirement.
c) To reduce the PCB trace resistance and inductance, same
ground returns paths should be as short as possible. If possible, make the output traces short and equal in length.
d) To reduce the PCB trace resistance and inductance,
ground returns paths should be as short as possible.
e) If possible, star ground or a single point ground should be
observed. Advanced planning before starting the PCB can
improve audio performance.
(7)
When using a bipolar output stage with the LME49810 (as in
Figure 1), the designer must beware of thermal runaway.
Thermal runaway is a result of the temperature dependence
of VBE (an inherent property of the transistor). As temperature
increases, VBE decreases. In practice, current flowing through
a bipolar transistor heats up the transistor, which lowers the
VBE. This in turn increases the current gain, and the cycle repeats. If the system is not designed properly this positive
feedback mechanism can destroy the bipolar transistors used
in the output stage. One of the recommended methods of
preventing thermal runaway is to use the same heat sink on
the bipolar output stage transistor together with VBE multiplier
transistor. When the VBE multiplier transistor is mounted to the
same heat sink as the bipolar output stage transistors, it temperature will track that of the output transistors. Its VBE is
dependent upon temperature as well, and so it will draw more
current as the output transistors heat up, reducing the bias
voltage to compensate. This will limit the base current into the
output transistors, which counteracts thermal runaway. Another widely popular method of preventing thermal runaway
is to use low value emitter degeneration resistors (RE1 and
RE2). As current increases, the voltage at the emitter also increases, which decreases the voltage across the base and
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LME49810
emitter. This mechanism helps to limit the current and counteracts thermal runaway.
can eliminate the trim pot and virtually eliminate crossover
distortion. The VCE voltage of QMULT (also called BIAS of the
output stage) can be set by following formula:
LME49810
Demo Board Schematic
20216707
FIGURE 4. LME49810 Test demo board schematic
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LME49810
Demonstration Board Layout
20216704
Silkscreen Layer
20216706
Top Layer
17
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LME49810
20216703
Bottom Layer
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LME49810
Revision History
Rev
Date
Description
1.0
05/24/07
Initial WEB release.
1.01
05/29/07
Few text edits.
1.02
09/17/07
Edited curve 20216724.
19
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LME49810
Physical Dimensions inches (millimeters) unless otherwise noted
TO–247 15–Lead Package
Order Number LME49810TB
NS Package Number TB15A
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LME49810
Notes
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LME49810 200V Audio Power Amplifier Driver with Baker Clamp
Notes
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