LME49811 [TI]
Audio Power Amplifier Series High Fidelity 200 Volt Power Amplifier Input Stage with Shutdown;
| 型号： | LME49811 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | Audio Power Amplifier Series High Fidelity 200 Volt Power Amplifier Input Stage with Shutdown |
| 文件： | 总19页 (文件大小：415K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LME49811
www.ti.com
SNAS394C –DECEMBER 2007–REVISED APRIL 2013
LME49811 Audio Power Amplifier Series High Fidelity 200 Volt Power Amplifier Input
Stage with Shutdown
Check for Samples: LME49811
1
FEATURES
DESCRIPTION
The LME49811 is a high fidelity audio power amplifier
input stage designed for demanding consumer and
pro-audio applications. 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 regulation.
2
•
Very High Voltage Operation
Scalable Output Power
Minimum External Components
External Compensation
Thermal Shutdown
•
•
•
•
APPLICATIONS
The LME49811 includes thermal shut down circuitry
that activates when the die temperature exceeds
150°C. The LME49811's shutdown function when
activated, forces the LME49811 into shutdown state.
•
•
•
•
•
•
Powered Subwoofers
Pro Audio
Powered Studio Monitors
Audio Video Receivers
Guitar Amplifiers
High Voltage Industrial Applications
KEY SPECIFICATIONS
•
•
•
•
Wide Operating Voltage Range: ±20V to ±100V
PSRR (f = DC): 115dB (Typ)
THD+N (f = 1kHz): 0.00035% (Typ)
Output Drive Current: 9mA
TYPICAL APPLICATION
R
F
56 kW
+V
CC
C
C
+V
CC
30 pF
Q
DAR
N
+
C
S
0.1 mF
R
B2
R
E1
0.22W
MULT
C
R
IN
IN
1.2 kW
10 mF 1.8 kW
IN-
Q
Source
Sink
-
R
E2
C
R
i
R
B1
i
0.22W
10 mF 1.8 kW
500W
IN+
SD
+
R
S
Q
DAR
P
56 kW
+5V
Shutdown
Circuitry
GND
-V
EE
R
M
1.4 kW
C
S
+
-V
0.1 mF
EE
Figure 1. Typical Audio Amplifier Application Circuit
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2007–2013, Texas Instruments Incorporated
LME49811
SNAS394C –DECEMBER 2007–REVISED APRIL 2013
www.ti.com
Connection Diagram
+V
15
14
13
12
CC
SOURCE
SINK
NC
NC
EE
11
10
9
-V
NC
8
NC
NC
7
COMP
6
5
4
3
2
IN-
IN+
GND
SD
1
NC
Figure 2. Top View
See Package Number NDN0015A
PIN DESCRIPTIONS
Pin
1
Pin Name
NC
Description
No Connect, Pin electrically isolated
2
SD
GND
IN+
Shutdown Control
Device Ground
3
4
Non-Inverting Input
Inverting Input
5
IN-
6
Comp
NC
External Compensation Connection
No Connect, Pin electrically isolated
No Connect, Pin electrically isolated
No Connect, Pin electrically isolated
Negative Power Supply
7
8
NC
9
NC
10
11
12
13
14
15
-VEE
NC
No Connect, Pin electrically isolated
No Connect, Pin electrically isolated
Output Sink
NC
Sink
Source
+VCC
Output Source
Positive Power Supply
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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SNAS394C –DECEMBER 2007–REVISED APRIL 2013
ABSOLUTE MAXIMUM RATINGS(1)(2)
Supply Voltage |V+| + |V-|
Differential Input Voltage
200V
+/-6V
Common Mode Input Range
Power Dissipation(3)
0.4 VEE to 0.4 VCC
4W
ESD Rating(4)
2kV
ESD Rating(5)
200V
(6)
Junction Temperature (TJMAX
Soldering Information
Storage Temperature
Thermal Resistance
)
150°C
NDN Package (10 seconds)
260°C
-40°C to +150°C
73°C/W
θJA
θJC
4°C/W
(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
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(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.
(4) Human body model, applicable std. JESD22-A114C.
(5) Machine model, applicable std. JESD22-A115-A.
(6) The maximum operating junction temperature is 150°C.
OPERATING RATINGS(1)(2)
Temperature Range
TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +85°C
Supply Voltage |V+| + |V-|
+/-20V ≤ VTOTAL ≤ +/-100V
(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
(2) The Electrical Characteristics tables list ensured 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 ensured.
Copyright © 2007–2013, Texas Instruments Incorporated
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SNAS394C –DECEMBER 2007–REVISED APRIL 2013
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ELECTRICAL CHARACTERISTICS +VCC = -VEE = 50V(1)(2)
The following specifications apply for ISD = 1.5mA, Figure 1, unless otherwise specified. Limits apply for TA = 25°C, CC =
30pF.
Symbol
Parameter
Conditions
LME49811
Units
(Limits)
Typical(3)
Limit(4)
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
VCM = 0V, VO = 0V, IO = 0A
ICC
IEE
14
16
17
mA (max)
mA (max)
% (max)
Total Quiescent Power Supply
Current
19
Total Harmonic Distortion +
Noise
No load, AV = 29dB
VOUT = 20VRMS, f = 1kHz
THD+N
AV
0.00055
0.0015
26
Closed Loop Voltage Gain
dB (min)
dB
VIN = 1mVRMS, f = 1kHz
f = DC
93
120
33
AV
Open Loop Gain
dB
VOM
VNOISE
IOUT
ISD
Output Voltage Swing
Output Noise
THD+N = 0.05%, Freq = 20Hz to 20kHz
LPF = 30kHz, Av = 29dB
A-weighted
VRMS
μV
100
70
180
6.5
μV (max)
mA(min)
Output Current
Outputs Shorted
8
1
2
mA(min)
mA (max)
Current into Shutdown Pin
To put part in “play” mode
1.5
16
VIN = 1.2VP-P, f = 10kHz square Wave,
Outputs shorted
SR
Slew Rate
13
3
V/μs (min)
VOS
IB
Input Offset Voltage
VCM = 0V, IO = 0mA
VCM = 0V, IO = 0mA
DC, Input Referred
1
mV (max)
nA
Input Bias Current
100
115
PSRR
Power Supply Rejection Ratio
105
dB (min)
(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
(2) The Electrical Characteristics tables list ensured 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 ensured.
(3) 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 ensured.
(4) Data sheet min/max specification limits are ensured by test or statistical analysis.
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ELECTRICAL CHARACTERISTICS +VCC = –VEE = 100V(1)(2)
The following specifications apply for ISD = 1.5mA, Figure 1, unless otherwise specified. Limits apply for TA = 25°C.
Symbol
Parameter
Conditions
LME49811
Units
(Limits)
Typical(3)
Limit(4)
Total Quiescent Power Supply
Current
ICC
IEE
VCM = 0V, VO = 0V, IO = 0A
VCM = 0V, VO = 0V, IO = 0A
17
19
22
mA (max)
mA (max)
% (max)
Total Quiescent Power Supply
Current
24
Total Harmonic Distortion +
Noise
No load, AV = 30dB
VOUT = 30VRMS, f = 1kHz
THD+N
AV
0.00035
0.001
26
Closed Loop Voltage Gain
dB (min)
dB
VIN = 1mVRMS, f = 1kHz
f = DC
93
120
68
AV
Open Loop Gain
dB
VOM
VNOISE
IOUT
ISD
Output Voltage Swing
Output Noise
THD+N = 0.05%, Freq = 20Hz to 20kHz
LPF = 30kHz, Av = 29dB
A-weighted
VRMS
μV
100
70
180
7
μV (max)
mA(min)
Output Current
Outputs Shorted
9
1
2
mA(min)
mA (max)
Current into Shutdown Pin
To put part in “play” mode
1.5
17
VIN = 1.2VP-P, f = 10kHz square Wave,
Outputs shorted
SR
Slew Rate
14
3
V/μs (min)
VOS
IB
Input Offset Voltage
VCM = 0V, IO = 0mA
VCM = 0V, IO = 0mA
f = DC, Input Referred
1
mV (max)
nA (max)
dB (min)
Input Bias Current
100
115
PSRR
Power Supply Rejection Ratio
105
(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
(2) The Electrical Characteristics tables list ensured 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 ensured.
(3) 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 ensured.
(4) Data sheet min/max specification limits are ensured by test or statistical analysis.
Copyright © 2007–2013, Texas Instruments Incorporated
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TYPICAL PERFORMANCE CHARACTERISTICS
Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 30pF, and TA = 25°C except where specified.
THD+N vs Frequency
+VCC = –VEE = 100V, VO = 14V
THD+N vs Frequency
+VCC = –VEE = 100V, VO = 30V
10
10
1
0.1
1
0.1
0.01
0.01
BW = 80 kHz
BW = 80 kHz
0.001
0.001
BW = 30 kHz
BW = 30 kHz
100
0.0001
0.0001
20
1k
20k
10k
10k
20
100
1k
20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 3.
Figure 4.
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 10V
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 20V
10
10
1
0.1
1
0.1
0.01
0.01
BW = 80 kHz
BW = 30 kHz
BW = 80 kHz
BW = 30 kHz
0.001
0.001
0.0001
0.0001
10k
20
100
1k
20k
20
100
1k
20k
10k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 5.
Figure 6.
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 5V
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 10V
10
10
1
0.1
1
0.1
BW = 80 kHz
0.01
0.01
BW = 80 kHz
0.001
0.001
BW = 30 kHz
100
BW = 30 kHz
0.0001
0.0001
10k
20
100
1k
20k
20
1k
10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 7.
Figure 8.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 30pF, and TA = 25°C except where specified.
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 20Hz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20Hz
10
10
1
0.1
1
0.1
BW = 80 kHz
BW = 80 kHz
0.01
0.01
BW = 30 kHz
BW = 30 kHz
0.001
0.001
0.0001
0.0001
1
10
100m
1
2
10 20
50
100m
50 100
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
Figure 9.
Figure 10.
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 1kHz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 1kHz
10
10
1
0.1
1
0.1
BW = 80 kHz
BW = 80 kHz
0.01
0.01
BW = 30 kHz
0.001
0.001
BW = 30 kHz
0.0001
0.0001
1
10
100m
1
2
10 20
50
100m
50 100
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
Figure 11.
Figure 12.
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 20kHz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20kHz
10
10
1
0.1
1
0.1
BW = 80 kHz
BW = 80 kHz
0.01
0.01
BW = 30 kHz
BW = 30 kHz
0.001
0.001
0.0001
0.0001
100m
1
2
10 20
50
100m
1
10
50 100
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
Figure 13.
Figure 14.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 30pF, and TA = 25°C except where specified.
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20kHz
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 1kHz
10
10
1
0.1
1
0.1
BW = 80 kHz
BW=80 kHz
0.01
0.01
BW = 30 kHz
BW=30 kHz
0.001
0.001
0.0001
0.0001
100m
1
2
10 20
100m
1
2
10 20
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
Figure 15.
Figure 16.
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20kHz
Closed Loop Frequency Response
+VCC = –VEE = 50V, VIN = 1VRMS
10
3
2
1
0.1
1
0
BW = 80 kHz
0.01
-1
-2
BW = 30 kHz
0.001
0.0001
-3
10k
100m
1
2
10 20
20
100
1k
200k
FREQUENCY (Hz)
OUTPUT VOLTAGE (Vrms)
Figure 17.
Figure 18.
Closed Loop Frequency Response
+VCC = –VEE = 100V, VIN = 1VRMS
Output Voltage vs Supply Voltage
3
2
100
80
60
1
0
THD+N = 1%
40
20
0
-1
-2
THD+N = 0.05%
-3
10k
20
100
1k
200k
0
20
40
60
80
100
SUPPLY VOLTAGE (±V)
FREQUENCY (Hz)
Figure 19.
Figure 20.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Data taken with Bandwidth = 30kHz, AV = 29dB, CC = 30pF, and TA = 25°C except where specified.
PSRR vs Frequency
+VCC = –VEE = 100V, No Filters
Input Referred, VRIPPLE = 1VRMS on VCC pin
0
PSRR vs Frequency
+VCC = –VEE = 50V, No Filters
Input Referred, VRIPPLE = 1VRMS on VCC pin
0
-20
-40
-20
-40
-60
-60
-80
-80
-100
-120
-140
-100
-120
-140
1k
10k
20
100
100k
100
1k
10k
100k
20
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 21.
Figure 22.
PSRR vs Frequency
PSRR vs Frequency
+VCC = –VEE = 100V, No Filters
+VCC = –VEE = 50V, No Filters
Input Referred, VRIPPLE = 1VRMS on VEE pin
Input Referred, VRIPPLE = 1VRMS on VEE pin
0
0
-20
-40
-60
-20
-40
-60
-80
-80
-100
-120
-100
-120
-140
100
1k
10k
20
100
100k
1k
10k
20
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 23.
Figure 24.
Open Loop and Phase Upper-Phase
Lower Gain
Supply Current vs Supply Voltage
180
160
28
24
20
16
12
8
203
180
140
120
100
80
158
135
113
90
I
EE
I
CC
60
68
45
23
0
40
20
0
4
-20
-23
0
20 30 40 50
60 70 80 90 100
10 100 1k 10k 100k 1M 10M 100M
SUPPLY VOTAGE (±V)
FREQUENCY (Hz)
Figure 25.
Figure 26.
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TEST CIRCUIT
R
F
56 kW
+V
CC
+
C
S
0.1 mF
C
i
R
C
C
i
22 mF
30 pF
1.8 kW
-
C
R
IN
IN
10 mF
1.8 kW
Test
Signal
Input
+
R
S
56 kW
C
S
0.1 mF
+
-V
EE
R
M
1.4 kW
Shutdown
Circuitry
5V
Figure 27. Test Circuit
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 shutdown 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 shutdown pin power supply. Slowly increasing the shutdown current 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, 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 in a Schmitt Trigger fashion 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.
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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.
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
resistances, 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 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 analogous to
voltage drops, the power dissipation out of the LME49811 is equal to the following:
PDMAX = (TJMAX−TAMB) / θJA
where
•
•
•
TJMAX = 150°C
TAMB is the system ambient temperature
θJA = θJC + θCS + θSA
(1)
Once the maximum package power dissipation has been calculated 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 response 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)
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If an input coupling capacitor 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. When using a input coupling capacitor RIN is needed to
set the DC bias point on the amplifier's input terminal. The resulting -3dB frequency response due to the
combination of CIN and RIN can be found from Equation (5) shown below:
fIN = 1 / (2πRINCIN) (Hz)
(5)
With large values of RIN oscillations may be observed on the outputs when the inputs are left floating. Decreasing
the value of RIN or not letting the inputs float will remove the oscillations. If the value of RIN is decreased then the
value of CIN will need to increase in order to maintain the same -3dB frequency response.
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 LME49811 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.
SUPPLY BYPASSING
The LME49811 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.
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 or additional driver stages. 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 TECHNIQUES
AND AVOIDING THERMAL RUNAWAY for additional information.
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. 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, 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:
VBIAS = VBE(1+RB2/RB1
)
(V)
(6)
When using a bipolar output stage with the LME49811 (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
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SNAS394C –DECEMBER 2007–REVISED APRIL 2013
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 emitter. This mechanism helps to limit the
current and counteracts thermal runaway.
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
LME49811 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 accommodate 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.
Demonstration Board Layout
Figure 28. Silkscreen Layer
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Figure 29. Top Layer
Figure 30. Bottom Layer
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SNAS394C –DECEMBER 2007–REVISED APRIL 2013
REVISION HISTORY
Rev
1.0
Date
Description
12/19/07
01/04/08
Initial release.
1.01
Edited the project title (replaced “Driver” with “Power Amplifier Input
Stage”.
1.02
C
11/11/09
04/05/13
Fixed the spacing between the equations 3, 4, 5, and 6 to the units
measures.
Changed layout of National Data Sheet to TI format.
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PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2016
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(6)
(3)
(4/5)
LME49811TB/NOPB
OBSOLETE TO-OTHER
NDN
15
TBD
Call TI
Call TI
-20 to 75
LME49811
TB
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2016
Addendum-Page 2
MECHANICAL DATA
NDN0015A
TB15A (Rev A)
www.ti.com
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