LM4991 [TI]
3W Audio Power Amplifier with Shutdown Mode;
| 型号： | LM4991 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 3W Audio Power Amplifier with Shutdown Mode |
| 文件： | 总22页 (文件大小：989K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
LM4991
3W Audio Power Amplifier with Shutdown Mode
Check for Samples: LM4991
1
FEATURES
DESCRIPTION
The LM4991 is a mono bridged audio power amplifier
capable of delivering 3W of continuous average
power into a 3Ω load with less than 10% THD when
powered by a 5V power supply (see Note below). To
conserve power in portable applications, the
LM4991's micropower shutdown mode (ISD = 0.1µA,
typ) is activated when VDD is applied to the
SHUTDOWN pin.
2
•
Available in Space-Saving WSON and SOIC
Packages
•
•
•
Ultra Low Current Shutdown Mode
Can Drive Capacitive Loads up to 500pF
Improved Click and Pop Circuitry Reduces
Noises During Turn-On and Turn-Off
Transitions
Boomer audio power amplifiers are designed
specifically to provide high power, high fidelity audio
output. They require few external components and
operate on low supply voltages from 2.2V to 5.5V.
Since the LM4991 does not require output coupling
capacitors, bootstrap capacitors, or snubber
networks, it is ideally suited for low-power portable
systems that require minimum volume and weight.
•
•
2.2 - 5.5V Operation
No Output Coupling Capacitors, Snubber
Networks, Bootstrap Capacitors or Gain-
Setting Resistors Required
•
Unity-Gain Stable
APPLICATIONS
Additional LM4991 features include thermal shutdown
protection, unity-gain stability, and external gain set.
•
•
•
•
Wireless and Cellular Handsets
PDAs
Note: An LM4991LD that has been properly mounted
to a circuit board will deliver 3W into 3Ω (at 10%
THD). The other package options for the LM4991 will
deliver 1.5W into 8Ω (at 10% THD). See the
Portable Computers
Desktop Computers
KEY SPECIFICATIONS
Application
information
LM4991M.
Information
concerning
sections
the LM4991LD
for
further
and
•
Improved PSRR at 217kHz and 1kHz: 64 dB
(typ)
•
PO at VDD = 5.0V, 10% THD, 1kHz
–
LM4991LD (only), 3Ω, 4Ω: 3W (typ), 2.5 W
(typ)
–
All packages, 8Ω load: 1.5 W (typ)
•
Shutdown current: 0.1µA (typ)
Connection Diagrams
Top View
Top View
Figure 1. SOIC Package
See Package Number D0008A
Figure 2. WSON Package
See Package Number NGN0008A
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.
All trademarks are the property of their respective owners.
2
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 © 2004–2013, Texas Instruments Incorporated
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
Typical Application
Figure 3. Typical Audio Amplifier Application Circuit
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.
Absolute Maximum Ratings(1)(2)
Supply Voltage
6.0V
−65°C to +150°C
−0.3V to VDD to +0.3V
Internally Limited
2000V
Supply Temperature
Input Voltage
Power Dissipation(3)
ESD Susceptibility(4)
ESD Susceptibility(5)
Junction Temperature
Thermal Resistance
200V
150°C
θJC (LD)(6)
θJA (LD)
4.3°C/W
56°C/W
θJC (MA)
θJA (MA)
35°C/W
140°C/W
(1) 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 ensure specific performance limits. Electrical Characteristics VDD= 5V state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensure for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(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. For the LM4991, TJMAX = 150°C. For the θJA's for different packages, please see theApplication Information section or the
Absolute Maximum Ratings section.
(4) Human body model, 100pF discharged through a 1.5kΩ resistor.
(5) Machine Model, 220pF–240pF discharged through all pins.
(6) The given θJA is for an LM4991 packaged in an LDC08A with the Exposed–DAP soldered to an exposed 1in2 area of 1oz printed circuit
board copper.
Operating Ratings
Temperature Range
T
MIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +85°C
2.2V ≤ VDD ≤ 5.5V
Supply Voltage
2
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
(1) (2)
Electrical Characteristics VDD = 5V
The following specifications apply for VDD = 5V and RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C.
LM4991
Parameter
Test Conditions
Units
(Limits)
Typ(3)
Limit(4)
Quiescent Power Supply Current VIN = 0V, no Load
3
4
7
IDD
mA (max)
VIN = 0V, RL = 8Ω
10
2.0
ISD
Shutdown Current
Shutdown Voltage
VSHUTDOWN = VDD
0.1
1.5
1.3
5
µA (max)
V
VSDIH
VSDIL
VOS
V
Output Offset Voltage
35
mV (max)
W (min)
(5)
(5)
THD = 1% (max), f = 1kHz
THD+N = 10%, f = 1kHz
LM4991LD, RL = 3Ω
LM4991LD, RL = 4Ω
LM4991, RL = 8Ω
2.38
2.1
1.3
3
0.9
Po
Output Power
(5)
(5)
LM4991LD, RL = 3Ω
LM4991LD, RL = 4Ω
LM4991, RL = 8Ω
2.5
1.5
0.2
W
THD+N
PSRR
Total Harmonic Distortion+Noise PO = 0.5W, f = 1kHz
%
Power Supply Rejection Ratio
VRIPPLE = 200mV sine p-p,
Input terminated with 10Ω,
f = 1kHz
64
55
dB (min)
(1) 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 ensure specific performance limits. Electrical Characteristics VDD= 5V state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensure for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(2) All voltages are measured with respect to the ground pin, unless otherwise specified.
(3) Typicals are specified at 25°C and represent the parametric norm.
(4) Limits are ensured to AOQL (Average Outgoing Quality Level).
(5) When driving 3Ω or 4Ω loads from a 5V supply, the LM4991LD must be mounted to a circuit board.
(1) (2)
Electrical Characteristics VDD = 3V
The following specifications apply for VDD = 3V and RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C.
LM4991
Parameter
Test Conditions
Units
(Limits)
Typ(3)
Limit(4)
IDD
Quiescent Power Supply
Current
VIN = 0V, no Load
VIN = 0V, RL = 8Ω
VSHUTDOWN = VDD
3
4
7
7
mA
(max)
ISD
Shutdown Current
0.1
1.1
0.9
5
2.0
µA (max)
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
V
V
35
mV
(max)
Po
Output Power
THD = 1% (max), f = 1kHz
PO = 0.25W, f = 1kHz
RL = 4Ω
RL = 8Ω
600
425
mW
%
Total Harmonic
Distortion+Noise
THD+N
0.1
(1) 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 ensure specific performance limits. Electrical Characteristics VDD= 5V state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensure for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(2) All voltages are measured with respect to the ground pin, unless otherwise specified.
(3) Typicals are specified at 25°C and represent the parametric norm.
(4) Limits are ensured to AOQL (Average Outgoing Quality Level).
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
3
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
Electrical Characteristics VDD = 3V (1) (2) (continued)
The following specifications apply for VDD = 3V and RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C.
LM4991
Parameter
Test Conditions
Units
(Limits)
Typ(3)
Limit(4)
PSRR
Power Supply Rejection Ratio VRIPPLE = 200mV sine p-p,
Input terminated with 10Ω,
68
dB
f = 1kHz
(1) (2)
Electrical Characteristics VDD = 2.6V
The following specifications apply for VDD = 2.6V and RL = 8Ω unless otherwise specified. Limits apply for TA = 25°C.
LM4991
Parameter
Test Conditions
Units
(Limits)
Typ(3)
Limits(4)
Quiescent Power Supply Current VIN = 0V, no Load
2
3
IDD
mA (max)
VIN = 0V, RL = 8Ω
ISD
Shutdown Current
VSHUTDOWN = VDD
0.1
1
µA(max)
VSDIH
VSDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
V
0.9
5
V
mV (max)
mW
35
THD = 1% (max), f = 1kHz
RL = 4Ω
RL = 8Ω
400
300
0.1
Po
Output Power
%
THD+N
PSRR
Total Harmonic Distortion+Noise PO = 0.15W, f = 1kHz
Power Supply Rejection Ratio
VRIPPLE = 200mV sine p-p,
Input terminated with 10Ω,
f = 1kHz
51
dB
(1) 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 ensure specific performance limits. Electrical Characteristics VDD= 5V state DC and AC
electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within
the Operating Ratings. Specifications are not ensure for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(2) All voltages are measured with respect to the ground pin, unless otherwise specified.
(3) Typicals are specified at 25°C and represent the parametric norm.
(4) Limits are ensured to AOQL (Average Outgoing Quality Level).
External Components Description
(Figure 3)
Components
Functional Description
1.
Ri
Inverting input resistance that sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass filter
with Ci at fC= 1/(2π RiCi).
2.
Ci
Input coupling capacitor that blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter with
Ri at fc = 1/(2π RiCi). Refer to the section, PROPER SELECTION OF EXTERNAL COMPONENTS, for an explanation
of how to determine the value of Ci.
3.
4.
Rf
Feedback resistance that sets the closed-loop gain in conjunction with Ri.
CS
Supply bypass capacitor that provides power supply filtering. Refer to the POWER SUPPLY BYPASSING section for
information concerning proper placement and selection of the supply bypass capacitor.
5.
CB
Bypass pin capacitor that provides half-supply filtering. Refer to the section, PROPER SELECTION OF EXTERNAL
COMPONENTS, for information concerning proper placement and selection of CB.
4
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
Typical Performance Characteristics
LD and MA Specific Characteristics
THD+N vs Frequency
VDD = 5V, RL = 4Ω, and PO = 1W
THD+N vs Output Power
VDD = 5V, RL = 4Ω, and f = 1 kHz
10
1
10
1
0.1
0.1
0.01
0.01
20
100
1k
FREQUENCY (Hz)
Figure 4.
10k 20k
10m
100m
1
3
OUTPUT POWER (W)
Figure 5.
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
5
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics
THD+N vs Frequency
VDD = 5V, RL = 8Ω, and PO = 500mW
THD+N vs Frequency
VDD = 3V, RL = 4Ω, and PO = 500mW
10
1
10
1
0.1
0.1
0.01
0.01
20
100
1k
FREQUENCY (Hz)
Figure 6.
10k 20k
20
100
1k
FREQUENCY (Hz)
Figure 7.
10k 20k
THD+N vs Frequency
VDD = 3V, RL = 8Ω, and PO = 250mW
THD+N vs Frequency
VDD = 2.6V, RL = 4Ω, and PO = 150mW
10
1
10
1
0.1
0.1
0.01
0.01
20
100
1k
FREQUENCY (Hz)
Figure 8.
10k 20k
20
100
1k
FREQUENCY (Hz)
Figure 9.
10k 20k
THD+N vs Frequency
VDD = 2.6V, RL = 8Ω, and PO = 150mW
THD+N vs Output Power
VDD = 5V, RL = 8Ω, and f = 1kHz
10
1
10
1
0.1
0.1
0.01
0.01
20
100
1k
FREQUENCY (Hz)
Figure 10.
10k 20k
10m
100m
1
3
OUTPUT POWER (W)
Figure 11.
6
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
Typical Performance Characteristics (continued)
THD+N vs Output Power
VDD = 3V, RL = 4Ω, and f = 1kHz
THD+N vs Output Power
VDD = 3V, RL = 8Ω, and f = 1kHz
10
1
10
1
0.1
0.1
0.01
0.01
10m
100m
1
10m
100m
1
OUTPUT POWER (W)
Figure 12.
OUTPUT POWER (W)
Figure 13.
THD+N vs Output Power
VDD = 2.6V, RL = 4Ω, and f = 1kHz
THD+N vs Output Power
VDD = 2.6V, RL = 8Ω, and f = 1kHz
10
1
10
1
0.1
0.1
0.01
0.01
10m
100m
1
10m
100m
OUTPUT POWER (W)
Figure 15.
500m
OUTPUT POWER (W)
Figure 14.
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 5V, RL = 8Ω, input 10Ω terminated
VDD = 5V, RL = 8Ω, input floating
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
20
100
1k
10k 20k
20
100
1k
FREQUENCY (Hz)
Figure 16.
10k 20k
FREQUENCY (Hz)
Figure 17.
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
7
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 3V, RL = 8Ω, input floating
VDD = 3V, RL = 8Ω, input 10Ω terminated
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
20
100
1k
10k 20k
20
100
1k
10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 18.
Figure 19.
Power Supply Rejection Ratio (PSRR) vs Frequency
Power Supply Rejection Ratio (PSRR) vs Frequency
VDD = 2.6V, RL = 8Ω, input 10Ω terminated
VDD = 2.6V, RL = 8Ω, Input Floating
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
20
100
1k
10k 20k
20
100
1k
10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 20.
Figure 21.
Noise Floor, 5V, 8Ω
80kHz Bandwidth, Input to GND
Open Loop Frequency Response, 5V
Figure 22.
Figure 23.
8
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
Typical Performance Characteristics (continued)
Power Dissipation vs Output Power, VDD = 5V
Power Dissipation vs Output Power, VDD = 3V
1.4
0.5
0.45
4W
1.2
0.4
4W
1
0.35
8W
0.3
0.8
0.25
0.2
0.15
0.1
0.05
0
0.6
8W
0.4
0.2
0
0
0.5
1
1.5
2
2.5
0
0.2
0.4
0.6
0.8
1
OUTPUT POWER (W)
OUTPUT POWER (W)
Figure 24.
Figure 25.
Shutdown Hysteresis Voltage
VDD = 5V, SD Mode = VDD
Power Dissipation vs Output Power, VDD = 2.6V
0.4
0.35
4W
0.3
0.25
0.2
8W
0.15
0.1
0.05
0
0
0.1
0.2
0.4
0.5
0.6
0.3
OUTPUT POWER (W)
Figure 26.
Figure 27.
Shutdown Hysteresis Voltage
VDD = 3V, SD Mode = VDD
Shutdown Hysteresis Voltage
VDD = 2.6V, SD Mode = VDD
Figure 28.
Figure 29.
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
Output Power vs Supply Voltage, RL = 4Ω
Output Power vs Supply Voltage, RL = 8Ω
3
3.5
f = 1kHz
f = 1kHz
3
2.5
2.5
2
1.5
1
10% THD+N
2
1.5
1
10% THD+N
1% THD+N
1% THD+N
500m
500m
0
0
2.2
3
4
5
5.5
2.2
3
4
5
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Figure 30.
Figure 31.
Output Power vs Supply Voltage, RL = 16Ω
1000
Output Power vs Supply Voltage, RL = 32Ω
1000
900
800
700
600
500
400
300
200
100
0
900
800
700
600
500
400
300
200
100
0
f=1kHz
f=1kHz
10% THD+N
1% THD+N
10% THD+N
1% THD+N
2.2
3
4
5
5.5
2.2
3
4
5
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
Figure 32.
Figure 33.
Frequency Response vs Input Capacitor Size
Figure 34.
10
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
APPLICATION INFORMATION
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION
The LM4991's exposed-DAP (die attach paddle) package (LD) provides a low thermal resistance between the die
and the PCB to which the part is mounted and soldered. This allows rapid heat transfer from the die to the
surrounding PCB copper traces, ground plane, and surrounding air. The result is a low voltage audio power
amplifier that produces 2W at ≤ 1% THD with a 4Ω load. This high power is achieved through careful
consideration of necessary thermal design. Failing to optimize thermal design may compromise the LM4991's
high power performance and activate unwanted, though necessary, thermal shutdown protection.
The LD package must have its DAP soldered to a copper pad on the PCB. The DAP's PCB copper pad is
connected to a large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and
radiation area. Place the heat sink area on either outside plane in the case of a two-sided PCB, or on an inner
layer of a board with more than two layers. Connect the DAP copper pad to the inner layer or backside copper
heat sink area with 4(2x2) vias. The via diameter should be 0.012in-0.013in with a 1.27mm pitch. Ensure efficient
thermal conductivity by plating through the vias.
Best thermal performance is achieved with the largest practical heat sink area. If the heatsink and amplifier share
the same PCB layer, a nominal 2.5in2 area is necessary for 5V operation with a 4Ω load. Heatsink areas not
placed on the same PCB layer as the LM4991 should be 5in2 (min) for the same supply voltage and load
resistance. The last two area recommendations apply for 25°C ambient temperature. Increase the area to
compensate for ambient temperatures above 25°C. The LM4991's power de-rating curve in the Typical
Performance Characteristics shows the maximum power dissipation versus temperature. An example PCB layout
for the LD package is shown in the Demonstration Board Layout section. Further detailed and specific
information concerning PCB layout, fabrication, and mounting an LD (WSON) package is available from Texas
Instruments Package Engineering Group under application note AN-1187 (Literature Number SNOA401).
PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω
LOADS
Power dissipated by a load is a function of the voltage swing across the load and the load's impedance. As load
impedance decreases, load dissipation becomes increasingly dependant on the interconnect (PCB trace and
wire) resistance between the amplifier output pins and the load's connections. Residual trace resistance causes
a voltage drop, which results in power dissipated in the trace and not in the load as desired. For example, 0.1Ω
trace resistance reduces the output power dissipated by a 4Ω load from 2.0W to 1.95W. This problem of
decreased load dissipation is exacerbated as load impedance decreases. Therefore, to maintain the highest load
dissipation and widest output voltage swing, PCB traces that connect the output pins to a load must be as wide
as possible.
Poor power supply regulation adversely affects maximum output power. A poorly regulated supply's output
voltage decreases with increasing load current. Reduced supply voltage causes decreased headroom, output
signal clipping, and reduced output power. Even with tightly regulated supplies, trace resistance creates the
same effects as poor supply regulation. Therefore, making the power supply traces as wide as possible helps
maintain full output voltage swing.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 3, the LM4991 has two operational amplifiers internally, allowing for a few different amplifier
configurations. The first amplifier's gain is externally configurable; the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri
while the second amplifier's gain is fixed. Figure 3 shows that the output of amplifier one serves as the input to
amplifier two, which results in both amplifiers producing signals identical in magnitude, but 180° out of phase.
Consequently, the differential gain for the IC is
AVD= 2 *(Rf/Ri)
(1)
By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier
configuration where one side of its load is connected to ground.
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
11
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
www.ti.com
A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides
differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output
power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable
output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier's closed-
loop gain without causing excessive clipping, please refer to the AUDIO POWER AMPLIFIER DESIGN section.
Another advantage of the differential bridge output is no net DC voltage across load. This results from biasing
VO1 and VO2 at the same DC voltage, in this case VDD/2 . This eliminates the coupling capacitor that single
supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a single-ended configuration
forces a single supply amplifier's half-supply bias voltage across the load. The current flow created by the half-
supply bias voltage increases internal IC power dissipation and my permanently damage loads such as
speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. Equation (2) states the maximum power dissipation point for a bridge
amplifier operating at a given supply voltage and driving a specified output load.
PDMAX = 4*(VDD)2/(2π2RL)
(2)
Since the LM4991 has two operational amplifiers in one package, the maximum internal power dissipation is 4
times that of a single-ended ampifier. Even with this substantial increase in power dissipation, the LM4991 does
not require heatsinking under most operating conditions and output loading. From Equation (2), assuming a 5V
power supply and an 8Ω load, the maximum power dissipation point is 625 mW. The maximum power dissipation
point obtained from Equation (2) must not be greater than the power dissipation that results from Equation (3):
PDMAX = (TJMAX–TA)/θJA
(3)
For the SO package, θJA = 140°C/W. For the LD package soldered to a DAP pad that expands to a copper area
of 1.0in2 on a PCB, the LM4991's θJA is 56°C/W. TJMAX = 150°C for the LM4991. The θJA can be decreased by
using some form of heat sinking. The resultant θJA will be the summation of the θJC, θCS, and θSA. θJC is the
junction to case of the package (or to the exposed DAP, as is the case with the LD package), θCS is the case to
heat sink thermal resistance and θSA is the heat sink to ambient thermal resistance. By adding additional copper
area around the LM4991, the θJA can be reduced from its free air value for the SO package. Increasing the
copper area around the LD package from 1.0in2 to 2.0in2 area results in a θJA decrease to 46°C/W. Depending
on the ambient temperature, TA, and the θJA, Equation (3) can be used to find the maximum internal power
dissipation supported by the IC packaging. If the result of Equation (2) is greater than that of Equation (3), then
either the supply voltage must be decreased, the load impedance increased, the θJA decreased, or the ambient
temperature reduced. For the typical application of a 5V power supply, with an 8Ω load, and no additional
heatsinking, the maximum ambient temperature possible without violating the maximum junction temperature is
approximately 61°C provided that device operation is around the maximum power dissipation point and assuming
surface mount packaging. For the LD package in a typical application of a 5V power supply, with a 4Ω load, and
1.0in2 copper area soldered to the exposed DAP pad, the maximum ambient temperature is approximately 77°C
providing device operation is around the maximum power dissipation point. Internal power dissipation is a
function of output power. If typical operation is not around the maximum power dissipation point, the ambient
temperature can be increased. Refer to the Typical Performance Characteristics curves for power dissipation
information for different output powers and output loading.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and power supply pins should be as close to the LM4991 as
possible. The capacitor connected between the bypass pin and ground improves the internal bias voltage's
stability, producing improved PSRR. The improvements to PSRR increase as the bypass pin capacitor increases.
Typical applications employ a 5V regulator with 10µF and a 0.1µF bypass capacitors which aid in supply stability.
This does not eliminate the need for bypassing the supply nodes of the LM4991 with a 1µF tantalum capacitor.
The selection of bypass capacitors, especially CB, is dependent upon PSRR requirements, click and pop
performance as explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS, system cost,
and size constraints.
12
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4991 contains a shutdown pin to externally turn off
the amplifier's bias circuitry. This shutdown feature turns the amplifier off when a logic high is placed on the
shutdown pin. The trigger point between a logic low and logic high level is typically half- supply. It is best to
switch between ground and supply to provide maximum device performance. By switching the shutdown pin to
VDD, the LM4991 supply current draw will be minimized in idle mode. While the device will be disabled with
shutdown pin voltages less then VDD, the idle current may be greater than the typical value of 0.1µA. In either
case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes.
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry which
provides a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch in
conjunction with an external pull-up resistor. When the switch is closed, the shutdown pin is connected to ground
and enables the amplifier. If the switch is open, then the external pull-up resistor will disable the LM4991. This
scheme ensures that the shutdown pin will not float thus preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical to optimize
device and system performance. While the LM4991 is tolerant of external component combinations,
consideration to component values must be used to maximize overall system quality.
The LM4991 is unity-gain stable which gives a designer maximum system flexibility. The LM4991 should be used
in low gain configurations to minimize THD+N values, and maximize the signal to noise ratio. Low gain
configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1
Vrms are available from sources such as audio codecs. Please refer to the section, AUDIO POWER AMPLIFIER
DESIGN, for a more complete explanation of proper gain selection.
Besides gain, one of the major considerations is the closed-loop bandwidth of the amplifier. To a large extent, the
bandwidth is dictated by the choice of external components shown in Figure 3. The input coupling capacitor, Ci,
forms a first order high pass filter which limits low frequency response. This value should be chosen based on
needed frequency response for a few distinct reasons.
Selection Of Input Capacitor Size
Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized
capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have little ability to reproduce signals below 100Hz to
150Hz. Thus, using a large input capacitor may not increase actual system performance.
In addition to system cost and size, click and pop performance is effected by the size of the input coupling
capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally
1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable.
Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be
minimized.
Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value.
Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the
LM4991 turns on. The slower the LM4991's outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the
smaller the turn-on pop. Choosing CB equal to 1.0µF along with a small value of Ci (in the range of 0.1µF to
0.39µF), should produce a virtually clickless and popless shutdown function. While the device will function
properly, (no oscillations or motorboating), with CB equal to 0.1µF, the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is recommended in all but the most cost sensitive
designs.
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
13
Product Folder Links: LM4991
LM4991
SNAS217A –MAY 2004–REVISED APRIL 2013
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8Ω Audio Amplifier
www.ti.com
Given:
Power Output
Load Impedance
Input Level
1 Wrms
8Ω
1 Vrms
Input Impedance
Bandwidth
20 kΩ
100 Hz–20 kHz ± 0.25 dB
A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating
from the Output Power vs Supply Voltage graphs in theTypical Performance Characteristics section, the supply
rail can be easily found. A second way to determine the minimum supply rail is to calculate the required Vopeak
using Equation (3) and add the output voltage. Using this method, the minimum supply voltage would be (Vopeak
+ (VOD + VODBOT)), where V
and VOD are extrapolated from the Dropout Voltage vs Supply Voltage curve
TOP
BOT
OD
TOP
in the Typical Performance Characteristics section.
(4)
Using the Output Power vs Supply Voltage graph for an 8Ω load, the minimum supply rail is 4.6V. But since 5V is
a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom
that allows the LM4991 to reproduce peaks in excess of 1W without producing audible distortion. At this time, the
designer must make sure that the power supply choice along with the output impedance does not violate the
conditions explained in the POWER DISSIPATION section.
Once the power dissipation equations have been addressed, the required differential gain can be determined
from Equation (4).
(5)
Rf/Ri = AVD/2
(6)
From Equation (4), the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance was 20kΩ, and with a AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results
in an allocation of Ri = 20kΩ and Rf = 30kΩ. The final design step is to address the bandwidth requirements
which must be stated as a pair of −3dB frequency points. Five times away from a −3dB point is 0.17dB down
from passband response which is better than the required ±0.25dB specified.
fL = 100Hz/5 = 20Hz
fH = 20kHz * 5 = 100kHz
As stated in the External Components Description section, Ri in conjunction with Ci create a highpass filter.
Ci ≥ 1/(2π*20kΩ*20Hz) = 0.397µF; use 0.39µF
The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain,
AVD. With a AVD = 3 and fH = 100kHz, the resulting GBWP = 150kHz which is much smaller than the LM4991
GBWP of 4MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential
gain, the LM4991 can still be used without running into bandwidth limitations.
14
Submit Documentation Feedback
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4991
LM4991
www.ti.com
SNAS217A –MAY 2004–REVISED APRIL 2013
REVISION HISTORY
Changes from Original (April 2013) to Revision A
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
Copyright © 2004–2013, Texas Instruments Incorporated
Submit Documentation Feedback
15
Product Folder Links: LM4991
PACKAGE OPTION ADDENDUM
www.ti.com
12-Oct-2014
PACKAGING INFORMATION
Orderable Device
LM4991LD/NOPB
LM4991LDX/NOPB
LM4991MA/NOPB
LM4991MAX/NOPB
Status Package Type Package Pins Package
Eco Plan
Lead/Ball Finish
MSL Peak Temp
Op Temp (°C)
-40 to 85
Device Marking
Samples
Drawing
Qty
(1)
(2)
(6)
(3)
(4/5)
ACTIVE
WSON
WSON
SOIC
NGN
8
8
8
8
1000
Green (RoHS
& no Sb/Br)
CU SN
CU SN
CU SN
CU SN
Level-3-260C-168 HR
Level-3-260C-168 HR
Level-1-260C-UNLIM
Level-1-260C-UNLIM
L4991
L4991
ACTIVE
ACTIVE
ACTIVE
NGN
D
4500
95
Green (RoHS
& no Sb/Br)
-40 to 85
Green (RoHS
& no Sb/Br)
-40 to 85
LM49
91MA
SOIC
D
2500
Green (RoHS
& no Sb/Br)
-40 to 85
LM49
91MA
(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.
Addendum-Page 1
PACKAGE OPTION ADDENDUM
www.ti.com
12-Oct-2014
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 2
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
B0
K0
P1
W
Pin1
Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant
(mm) W1 (mm)
LM4991LD/NOPB
LM4991LDX/NOPB
LM4991MAX/NOPB
WSON
WSON
SOIC
NGN
NGN
D
8
8
8
1000
4500
2500
178.0
330.0
330.0
12.4
12.4
12.4
4.3
4.3
6.5
4.3
4.3
5.4
1.3
1.3
2.0
8.0
8.0
8.0
12.0
12.0
12.0
Q1
Q1
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-Apr-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SPQ
Length (mm) Width (mm) Height (mm)
LM4991LD/NOPB
LM4991LDX/NOPB
LM4991MAX/NOPB
WSON
WSON
SOIC
NGN
NGN
D
8
8
8
1000
4500
2500
213.0
367.0
367.0
191.0
367.0
367.0
55.0
35.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
NGN0008A
LDC08A (Rev B)
www.ti.com
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
amplifier.ti.com
dataconverter.ti.com
www.dlp.com
Automotive and Transportation www.ti.com/automotive
Communications and Telecom www.ti.com/communications
Amplifiers
Data Converters
DLP® Products
DSP
Computers and Peripherals
Consumer Electronics
Energy and Lighting
Industrial
www.ti.com/computers
www.ti.com/consumer-apps
www.ti.com/energy
dsp.ti.com
Clocks and Timers
Interface
www.ti.com/clocks
interface.ti.com
logic.ti.com
www.ti.com/industrial
www.ti.com/medical
Medical
Logic
Security
www.ti.com/security
Power Mgmt
Microcontrollers
RFID
power.ti.com
Space, Avionics and Defense
Video and Imaging
www.ti.com/space-avionics-defense
www.ti.com/video
microcontroller.ti.com
www.ti-rfid.com
www.ti.com/omap
OMAP Applications Processors
Wireless Connectivity
TI E2E Community
e2e.ti.com
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2014, Texas Instruments Incorporated
相关型号：
©2020 ICPDF网 联系我们和版权申明