TI1 LME49811 Audio power amplifier series high fidelity 200 volt power amplifier input stage with shutdown Datasheet

LME49811
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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
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.
1
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
RF
56 k:
+VCC
CC
+VCC
30 pF
QDARN
CS+
0.1 PF
CIN
RB2
RIN
10 PF 1.8 k:
1.2 k:
IN-
Ci
QMULT
Source
Ri
RB1
10 PF 1.8 k:
IN+
+
RE1
0.22:
500:
RE2
0.22:
Sink
RS
+5V
QDARP
56 k:
RM
SD Shutdown
GND
Circuitry
-VEE
1.4 k:
CS
0.1 PF +
-VEE
Figure 1. Typical Audio Amplifier Application Circuit
1
2
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.
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
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LME49811
Connection Diagram
15
+VCC
14
SOURCE
13
SINK
12
NC
11
10
9
8
7
6
5
4
3
2
1
-VEE
NC
NC
NC
NC
COMP
ININ+
GND
SD
NC
Figure 2. Top View
See Package Number NDN0015A
PIN DESCRIPTIONS
Pin
Pin Name
1
NC
No Connect, Pin electrically isolated
Description
2
SD
Shutdown Control
3
GND
4
IN+
Non-Inverting Input
5
IN-
Inverting Input
6
Comp
External Compensation Connection
7
NC
No Connect, Pin electrically isolated
8
NC
No Connect, Pin electrically isolated
9
NC
No Connect, Pin electrically isolated
10
-VEE
Negative Power Supply
11
NC
No Connect, Pin electrically isolated
12
NC
No Connect, Pin electrically isolated
13
Sink
Output Sink
14
Source
15
+VCC
Device Ground
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.
2
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ABSOLUTE MAXIMUM RATINGS (1) (2)
Supply Voltage |V+| + |V-|
200V
Differential Input Voltage
+/-6V
Common Mode Input Range
0.4 VEE to 0.4 VCC
Power Dissipation (3)
4W
(4)
2kV
ESD Rating (5)
200V
ESD Rating
Junction Temperature (TJMAX) (6)
Soldering Information
150°C
NDN Package (10 seconds)
Storage Temperature
Thermal Resistance
(1)
(2)
(3)
(4)
(5)
(6)
260°C
-40°C to +150°C
θJA
73°C/W
θJC
4°C/W
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
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
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.
Human body model, applicable std. JESD22-A114C.
Machine model, applicable std. JESD22-A115-A.
The maximum operating junction temperature is 150°C.
OPERATING RATINGS (1) (2)
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage |V+| + |V-|
(1)
(2)
−40°C ≤ TA ≤ +85°C
+/-20V ≤ VTOTAL ≤ +/-100V
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
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.
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LME49811
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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
Typical (3)
Limit (4)
Units
(Limits)
ICC
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
14
17
mA (max)
IEE
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
16
19
mA (max)
THD+N
Total Harmonic Distortion +
Noise
No load, AV = 29dB
VOUT = 20VRMS, f = 1kHz
0.00055
0.0015
% (max)
AV
Closed Loop Voltage Gain
26
dB (min)
AV
Open Loop Gain
VOM
Output Voltage Swing
VNOISE
Output Noise
IOUT
Output Current
VIN = 1mVRMS, f = 1kHz
93
f = DC
120
dB
dB
THD+N = 0.05%, Freq = 20Hz to 20kHz
33
VRMS
LPF = 30kHz, Av = 29dB
100
μV
A-weighted
70
180
μV (max)
Outputs Shorted
8
6.5
mA(min)
mA(min)
mA (max)
ISD
Current into Shutdown Pin
To put part in “play” mode
1.5
1
2
SR
Slew Rate
VIN = 1.2VP-P, f = 10kHz square Wave,
Outputs shorted
16
13
V/μs (min)
VOS
Input Offset Voltage
VCM = 0V, IO = 0mA
1
3
mV (max)
IB
Input Bias Current
VCM = 0V, IO = 0mA
100
PSRR
Power Supply Rejection Ratio
DC, Input Referred
115
105
dB (min)
(1)
(2)
(3)
(4)
4
nA
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
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.
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.
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
Typical
(3)
Limit
(4)
Units
(Limits)
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
Total Harmonic Distortion +
Noise
No load, AV = 30dB
VOUT = 30VRMS, f = 1kHz
0.00035
0.001
% (max)
AV
Closed Loop Voltage Gain
26
dB (min)
AV
Open Loop Gain
VOM
Output Voltage Swing
VNOISE
Output Noise
IOUT
VIN = 1mVRMS, f = 1kHz
93
f = DC
120
dB
THD+N = 0.05%, Freq = 20Hz to 20kHz
68
VRMS
LPF = 30kHz, Av = 29dB
100
A-weighted
70
180
μV (max)
Output Current
Outputs Shorted
9
7
mA(min)
ISD
Current into Shutdown Pin
To put part in “play” mode
1.5
1
2
mA(min)
mA (max)
SR
Slew Rate
VIN = 1.2VP-P, f = 10kHz square Wave,
Outputs shorted
17
14
V/μs (min)
VOS
Input Offset Voltage
VCM = 0V, IO = 0mA
1
3
mV (max)
IB
Input Bias Current
VCM = 0V, IO = 0mA
100
PSRR
Power Supply Rejection Ratio
f = DC, Input Referred
115
(1)
(2)
(3)
(4)
dB
μV
nA (max)
105
dB (min)
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
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.
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.
Data sheet min/max specification limits are ensured by test or statistical analysis.
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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
10
1
1
THD+N (%)
THD+N (%)
THD+N vs Frequency
+VCC = –VEE = 100V, VO = 30V
10
0.1
0.01
BW = 80 kHz
0.1
0.01
BW = 80 kHz
0.001
0.001
BW = 30 kHz
0.0001
BW = 30 kHz
0.0001
20
100
1k
20
10k 20k
100
FREQUENCY (Hz)
Figure 4.
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 10V
1
THD+N (%)
THD+N (%)
THD+N vs Frequency
+VCC = –VEE = 50V, VO = 20V
10
1
0.1
0.01
BW = 80 kHz
0.001
0.1
0.01
BW = 80 kHz
0.001
BW = 30 kHz
BW = 30 kHz
0.0001
20
100
1k
10k 20k
0.0001
20
100
FREQUENCY (Hz)
10
10k 20k
FREQUENCY (Hz)
Figure 6.
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 5V
THD+N vs Frequency
+VCC = –VEE = 20V, VO = 10V
10
1
THD+N (%)
THD+N (%)
1k
Figure 5.
1
0.1
BW = 80 kHz
0.01
0.001
0.1
0.01
BW = 80 kHz
0.001
BW = 30 kHz
BW = 30 kHz
0.0001
0.0001
20
100
1k
10k 20k
FREQUENCY (Hz)
20
100
1k
10k 20k
FREQUENCY (Hz)
Figure 7.
6
10k 20k
FREQUENCY (Hz)
Figure 3.
10
1k
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.
10
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 20Hz
10
1
THD+N (%)
THD+N (%)
1
0.1
BW = 80 kHz
0.01
0.001
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20Hz
BW = 30 kHz
0.0001
100m
0.1
BW = 80 kHz
0.01
0.001
1
2
10
20
50
BW = 30 kHz
0.0001
100m
1
Figure 9.
10
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 1kHz
10
THD+N (%)
THD+N (%)
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 1kHz
1
0.1
BW = 80 kHz
0.01
BW = 30 kHz
0.0001
100m
1
0.1
BW = 80 kHz
0.01
0.001
2
10
20
50
BW = 30 kHz
0.0001
100m
50 100
Figure 12.
THD+N vs Output Voltage
+VCC = –VEE = 50V, f = 20kHz
THD+N vs Output Voltage
+VCC = –VEE = 100V, f = 20kHz
10
1
THD+N (%)
THD+N (%)
10
Figure 11.
1
0.1
BW = 80 kHz
0.01
0.001
1
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
10
50 100
Figure 10.
1
0.001
10
OUTPUT VOLTAGE (Vrms)
OUTPUT VOLTAGE (Vrms)
BW = 30 kHz
0.0001
100m
1
0.1
BW = 80 kHz
0.01
0.001 BW = 30 kHz
2
10
20
50
0.0001
100m
OUTPUT VOLTAGE (Vrms)
1
10
50 100
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.
10
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20kHz
10
1
1
THD+N (%)
THD+N (%)
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 1kHz
0.1
BW = 80 kHz
0.01
BW = 30 kHz
0.001
0.0001
100m
1
0.1
BW=80 kHz
0.01
BW=30 kHz
0.001
2
10
0.0001
100m
20
OUTPUT VOLTAGE (Vrms)
1
20
Figure 16.
THD+N vs Output Voltage
+VCC = –VEE = 20V, f = 20kHz
3
Closed Loop Frequency Response
+VCC = –VEE = 50V, VIN = 1VRMS
2
1
1
0.1
GAIN (dB)
THD+N (%)
10
OUTPUT VOLTAGE (Vrms)
Figure 15.
10
2
BW = 80 kHz
0.01
0
-1
0.001
BW = 30 kHz
0.0001
100m
-2
-3
1
2
10
20
20
100
10k
200k
FREQUENCY (Hz)
OUTPUT VOLTAGE (Vrms)
Figure 17.
3
1k
Figure 18.
Closed Loop Frequency Response
+VCC = –VEE = 100V, VIN = 1VRMS
Output Voltage vs Supply Voltage
100
OUTPUT VOTLAGE (VRMS)
2
GAIN (dB)
1
0
-1
-2
-3
20
100
1k
10k
200k
THD+N = 1%
60
40
THD+N = 0.05%
20
0
0
20
40
60
80
100
SUPPLY VOLTAGE (±V)
FREQUENCY (Hz)
Figure 19.
8
80
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 = 50V, No Filters
Input Referred, VRIPPLE = 1VRMS on VCC pin
0
0
-20
-20
-40
-40
PSRR (dB)
PSRR (dB)
PSRR vs Frequency
+VCC = –VEE = 100V, No Filters
Input Referred, VRIPPLE = 1VRMS on VCC pin
-60
-80
-60
-80
-100
-100
-120
-120
-140
20
100
1k
10k
-140
20
100k
10k
100k
FREQUENCY (Hz)
Figure 21.
Figure 22.
PSRR vs Frequency
+VCC = –VEE = 100V, No Filters
Input Referred, VRIPPLE = 1VRMS on VEE pin
PSRR vs Frequency
+VCC = –VEE = 50V, No Filters
Input Referred, VRIPPLE = 1VRMS on VEE pin
0
0
-20
-20
-40
PSRR (dB)
PSRR (dB)
-40
-60
-80
-60
-80
-100
-100
-120
-120
20
100
1k
10k
-140
20
100k
100
Figure 23.
Open Loop and Phase Upper-Phase
Lower Gain
Supply Current vs Supply Voltage
158
120
135
100
113
80
90
60
68
40
45
20
23
0
0
1k
10k 100k 1M
24
SUPPLY CURRENT (mA)
180
140
100
100k
28
203
160
-20
10
10k
Figure 24.
PHASE (°)
180
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
GAIN (dB)
1k
100
FREQUENCY (Hz)
-23
10M 100M
20
IEE
16
ICC
12
8
4
0
20
30
40
50
60
70
80
90
100
SUPPLY VOTAGE (±V)
FREQUENCY (Hz)
Figure 25.
Figure 26.
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TEST CIRCUIT
RF
56 k:
+VCC
+ CS
0.1 PF
Ci
22 PF
Ri
CC
1.8 k:
30 pF
-
Test
Signal
Input
CIN
RIN
10 PF
1.8 k:
+
RS
56 k:
CS
+
RM
0.1 PF
-VEE
1.4 k:
5V
Shutdown
Circuitry
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.
10
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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 lowinductance 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
12
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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
14
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SNAS394C – DECEMBER 2007 – REVISED APRIL 2013
REVISION HISTORY
Rev
Date
1.0
12/19/07
Initial release.
Description
1.01
01/04/08
Edited the project title (replaced “Driver” with “Power Amplifier Input
Stage”.
1.02
11/11/09
Fixed the spacing between the equations 3, 4, 5, and 6 to the units
measures.
C
04/05/13
Changed layout of National Data Sheet to TI format.
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15
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
LME49811TB/NOPB
LIFEBUY
Package Type Package Pins Package
Drawing
Qty
TO-OTHER
NDN
15
24
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Green (RoHS
& no Sb/Br)
CU SN
Level-1-NA-UNLIM
Op Temp (°C)
Device Marking
(4/5)
-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
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
Addendum-Page 2
MECHANICAL DATA
NDN0015A
TB15A (Rev A)
www.ti.com
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