LM4902 [TI]
265mW 单声道、模拟输入 AB 类音频放大器;
| 型号： | LM4902 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 265mW 单声道、模拟输入 AB 类音频放大器 放大器 音频放大器 |
| 文件： | 总25页 (文件大小：1687K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
LM4902 Boomer™ Audio Power Amplifier Series 265mW at 3.3V Supply Audio Power
Amplifier with Shutdown Mode
Check for Samples: LM4902
1
FEATURES
DESCRIPTION
The LM4902 is a bridged audio power amplifier
capable of delivering 265mW of continuous average
power into an 8Ω load with 1% THD+N from a 3.3V
power supply.
23
•
VSSOP and WSON Packaging
•
No Output Coupling Capacitors, Bootstrap
Capacitors, or Snubber Circuits are Necessary
•
•
•
•
Thermal Shutdown Protection Circuitry
Unity-Gain Stable
Boomer™ audio power amplifiers were designed
specifically to provide high quality output power from
a low supply voltage while requiring a minimal
amount of external components. Since the LM4902
does not require output coupling capacitors, bootstrap
capacitors or snubber networks, it is optimally suited
for low-power portable applications.
External Gain Configuration Capability
Latest Generation "Click and Pop"
Suppression Circuitry
APPLICATIONS
The LM4902 features an externally controlled, low
power consumption shutdown mode, and thermal
shutdown protection.
•
•
•
Cellular Phones
PDA's
Any Portable Audio Application
The closed loop response of the unity-gain stable
LM4902 can be configured by external gain-setting
resistors.
KEY SPECIFICATIONS
•
•
•
THD+N at 1kHz for 265mW Continuous
Average Output Power into 8Ω, VDD = 3.3V
1.0% (max)
THD+N at 1kHz for 675mW Continuous
Average Output Power into 8Ω, VDD = 5V 1.0%
(max)
Shutdown Current 0.1µA (typ)
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
3
Boomer is a trademark of Texas Instruments.
All other 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 © 2001–2013, Texas Instruments Incorporated
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Typical Application
Figure 1. Typical Audio Amplifier Application Circuit
Connection Diagrams
Figure 2. VSSOP - Top View
See Package Number DGK
Figure 3. WSON - Top View
See Package Number NGL
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
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Absolute Maximum Ratings(1)(2)
Supply Voltage
6.0V
−65°C to +150°C
−0.3V to VDD + 0.3V
Internally limited
2000V
Storage Temperature
Input Voltage
Power Dissipation(3)
ESD Susceptibility(4)
ESD Susceptibility(5)
Junction Temperature
200V
150°C
Soldering Information
Small Outline Package
Vapor Phase (60 sec.)
215°C
220°C
Infrared (15 sec.)
θJC (VSSOP)
θJA (VSSOP)
θJA (WSON)
Thermal Resistance
56°C/W
190°C/W
67°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 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 ensured 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 TI 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 the Absolute Maximum Ratings,
whichever is lower. For the LM4902, TJMAX = 150°C. The typical junction-to-ambient thermal resistance, when board mounted, is
190°C/W for package number DGK.
(4) Human body model, 100pF discharged through a 1.5kΩ resistor.
(5) Machine Model, 220pF–240pF discharged through all pins.
Operating Ratings
Temperature Range TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +85°C
2.0V ≤ VDD ≤ 5.5V
Supply Voltage
Electrical Characteristics(1)(2)
The following specifications apply for VDD = 5V, for all available packages, unless otherwise specified. Limits apply for TA =
25°C.
LM4902
Units
(Limits)
Symbol
Parameter
Conditions
VIN = 0V, IO = 0A(6)
Typical(3)
Limit(4)(5)
IDD
Quiescent Power Supply Current
Shutdown Current
4
0.1
5
6.0
5
mA (max)
μA (max)
mV (max)
mW (min)
ISD
VOS
PO
VPIN1 =GND
Output Offset Voltage
Output Power
VIN = 0V
50
300
THD = 1% (max); f = 1kHz; RL = 8Ω;
PO = 400 mWrms; AVD = 2; RL = 8Ω;
20Hz ≤ f ≤ 20kHz, BW < 80kHz
675
THD+N
Total Harmonic Distortion+Noise
0.4
%
(1) All voltages are measured with respect to the ground pin, unless otherwise specified.
(2) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics 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 ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Limits are specified to TI's AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(6) The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
3
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Electrical Characteristics(1)(2) (continued)
The following specifications apply for VDD = 5V, for all available packages, unless otherwise specified. Limits apply for TA =
25°C.
LM4902
Typical(3) Limit(4)(5)
Units
(Limits)
Symbol
Parameter
Conditions
VRIPPLE = 200mV sine p-p
f = 217Hz(7)
f = 1KHz(7)
f = 217Hz(8)
f = 1KHz(8)
70
67
55
55
PSRR
Power Supply Rejection Ratio
dB
(7) Unterminated input.
(8) 10Ω terminated input.
4
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Electrical Characteristics(1)(2)
The following specifications apply for VDD = 3.3V, for all available packages, unless otherwise specified. Limits apply for TA =
25°C.
LM4902
Units
(Limits)
Symbol
Parameter
Conditions
VIN = 0V, IO = 0A(6)
Typical(3)
Limit(4)(5)
IDD
Quiescent Power Supply Current
Shutdown Current
3
0.1
5
5
3
mA (max)
μA (max)
mV (max)
mW
ISD
VOS
PO
VPIN1 = GND
Output Offset Voltage
Output Power
VIN = 0V
50
THD = 1% (max); f = 1kHz; RL = 8Ω;
PO = 250 mWrms; AVD = 2; RL = 8Ω;
20Hz ≤ f ≤ 20kHz, BW < 80kHz
VRIPPLE = 200mV sine p-p
f = 217Hz(7)
f = 1KHz(7)
f = 217Hz(8)
265
THD+N
Total Harmonic Distortion+Noise
Power Supply Rejection Ratio
0.4
%
73
70
60
68
PSRR
dB
f = 1KHz(8)
(1) All voltages are measured with respect to the ground pin, unless otherwise specified.
(2) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics 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 ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Limits are specified to TI's AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(6) The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
(7) Unterminated input.
(8) 10Ω terminated input.
Electrical Characteristics(1)(2)
The following specifications apply for VDD = 2.6V, for all available packages, unless otherwise specified. Limits apply for TA =
25°C.
LM4902
Units
(Limits)
Symbol
Parameter
Conditions
VIN = 0V, IO = 0A(6)
Typical(3)
Limit(4)(5)
IDD
Quiescent Power Supply Current
Shutdown Current
2.6
0.1
5
4
mA (max)
μA (max)
mV
ISD
VOS
PO
VPIN1 = VDD
2.0
Output Offset Voltage
Output Power
VIN = 0V
THD = 1% (max); f = 1kHz; RL = 8Ω
PO = 100 mWrms; AVD = 2; RL = 8Ω;
20Hz ≤ f ≤ 20kHz, BW < 80kHz
VRIPPLE = 200mV sine p-p
f = 217Hz(7)
130
mW
THD+N
Total Harmonic Distortion+Noise
0.4
%
PSRR
Power Supply Rejection Ratio
58
63
dB
f = 1KHz(7)
(1) All voltages are measured with respect to the ground pin, unless otherwise specified.
(2) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics 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 ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Limits are specified to TI's AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(6) The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
(7) 10Ω terminated input.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
5
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
External Components Description
(Figure 1)
Components
Functional Description
1.
Ri
Inverting input resistance which 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 which blocks the DC voltage at the amplifier's 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
CS
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
Supply bypass capacitor which 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 which provides half-supply filtering. Refer to the PROPER SELECTION OF EXTERNAL
COMPONENTS for information concerning proper placement and selection of CB.
6
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
Figure 4.
Figure 5.
THD+N vs Frequency
THD+N vs Frequency
Figure 6.
Figure 7.
THD+N vs Frequency
THD+N vs Frequency
Figure 8.
Figure 9.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
7
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
THD+N vs Frequency
THD+N vs Frequency
Figure 10.
Figure 11.
THD+N vs Frequency
THD+N vs Frequency
Figure 12.
Figure 13.
THD+N vs Frequency
THD+N vs Output Power
Figure 14.
Figure 15.
8
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Typical Performance Characteristics (continued)
THD+N vs Output Power
THD+N vs Output Power
Figure 16.
Figure 17.
THD+N vs Output Power
THD+N vs Output Power
Figure 18.
Figure 19.
THD+N vs Output Power
THD+N vs Output Power
Figure 20.
Figure 21.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
9
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
THD+N vs Output Power
THD+N vs Output Power
Figure 22.
Figure 23.
THD+N vs Output Power
THD+N vs Output Power
Figure 24.
Figure 25.
Output Power vs Supply Voltage
Output Power vs Supply Voltage
Figure 26.
Figure 27.
10
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Typical Performance Characteristics (continued)
Output Power vs Supply Voltage
Output Power vs Supply Voltage
Figure 28.
Figure 29.
Output Power vs Load Resistance
Power Dissipation vs Output Power
Figure 30.
Figure 31.
Power Dissipation vs Output Power
Power Dissipation vs Output Power
Figure 32.
Figure 33.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
11
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
Clipping Voltage vs Supply Voltage
Noise Floor
Figure 34.
Figure 35.
Noise Floor
Frequency Response vs Input Capacitor Size
Figure 36.
Figure 37.
Power Supply Rejection Ratio
Power Supply Rejection Ratio
Figure 38.
Figure 39.
12
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
Typical Performance Characteristics (continued)
Power Supply Rejection Ratio
Power Supply Rejection Ratio
Figure 40.
Figure 41.
Power Supply Rejection Ratio vs Supply Voltage
Power Supply Rejection Ratio vs Supply Voltage
Figure 42.
Figure 43.
Power Derating Curve
Supply Current vs Supply Voltage
Figure 44.
Figure 45.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
13
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Typical Performance Characteristics (continued)
Open Loop Frequency Response
LM4902NGL Power Derating Curve
This curve shows the LM4902NGL's thermal dissipation ability at
different ambient temperatures given the exposed-DAP of the part is
soldered to a plane of 1oz. Cu with an area given in the label of each
curve.
Figure 46.
Figure 47.
14
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
APPLICATION INFORMATION
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATION
The LM4902's exposed-DAP (die-attach paddle) package (NGL) provides a low thermal resistance between the
die and the PCB to which the part is mounted and soldered. This allows rapid heat from the die to the
surrounding PCB copper traces, ground plane, and surrounding air. This allows the LM4902NGL to operate at
higher output power levels in higher ambient temperatures than the DGK package. Failing to optimize thermal
design may compromise the high power performance and activate unwanted, though necessary, thermal
shutdown protection.
The NGL 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 2 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. The power derating curve in the
Typical Performance Characteristics shows the maximum power dissipation versus temperature for several
different areas of heat sink area. Placing the majority of the heat sink area on another plane is preferred as heat
is best dissipated through the bottom of the chip. For further detailed and specific information concerning PCB
layout, fabrication, and mounting an NGL (WSON) package, see the AN-1187 Application Report (Literature
Number SNOA401).
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4902 has two operational amplifiers internally, allowing for a few different amplifier
configurations. The first amplifier's gain is externally configurable, while 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 by the two internal 20kΩ resistors. Figure 1 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 out of phase 180°. 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.
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.
A bridge configuration, such as the one used in LM4902, also creates a second advantage over single-ended
amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across
the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single-
ended amplifier configuration. If an output coupling capacitor is not used in a single-ended configuration, the half-
supply bias across the load would result in both increased internal lC power dissipation as well as permanent
loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or
single-ended. 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 = (VDD)2/(2π2RL)
Single-Ended
(2)
However, a direct consequence of the increased power delivered to the load by a bridge amplifier is an increase
in internal power dissipation point for a bridge amplifier operating at the same conditions.
PDMAX = 4(VDD)2/(2π2RL)
Bridge Mode
(3)
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
15
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
Since the LM4902 has two operational amplifiers in one package, the maximum internal power dissipation is 4
times that of a single-ended amplifier. Even with this substantial increase in power dissipation, the LM4902 does
not require heatsinking. 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 3 must not be greater
than the power dissipation that results from Equation 4:
PDMAX = (TJMAX − TA)/θJA
(4)
For package DGK, θJA = 190°C/W. TJMAX = 150°C for the LM4902. Depending on the ambient temperature, TA,
of the system surroundings, Equation 4 can be used to find the maximum internal power dissipation supported by
the IC packaging. If the result of Equation 3 is greater than that of Equation 4, then either the supply voltage
must be decreased, the load impedance increased, the ambient temperature reduced, or the θJA reduced with
heatsinking. In many cases larger traces near the output, VDD, and Gnd pins can be used to lower the θJA. The
larger areas of copper provide a form of heatsinking allowing a higher power dissipation. For the typical
application of a 5V power supply, with an 8Ω load, the maximum ambient temperature possible without violating
the maximum junction temperature is approximately 30°C provided that 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
POWER SUPPLY BYPASSING
As with any power 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 device as
possible. The effect of a larger half supply bypass capacitor is improved PSRR due to increased half-supply
stability. Typical applications employ a 5V regulator with 10μF and a 0.1μF bypass capacitors which aid in supply
stability, but do not eliminate the need for bypassing the supply nodes of the LM4902. The selection of bypass
capacitors, especially CB, is thus dependent upon desired PSRR requirements, click and pop performance as
explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS, system cost, and size
constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4902 contains a shutdown pin to externally turn off
the amplifier's bias circuitry. This shutdown feature turns the amplifier off when a logic low 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 GND,
the LM4902 supply current draw will be minimized in idle mode. While the device will be disabled with shutdown
pin voltages greater than GND, 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 disables the amplifier. If the switch is open, then the external pull-up resistor will enable the LM4902. 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 LM4902 is tolerant to a variety of external component combinations,
consideration to component values must be used to maximize overall system quality.
The LM4902 is unity-gain stable, giving a designer maximum system flexibility. The LM4902 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 1. 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.
16
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
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 150Hz. In this
case using a large input capacitor may not increase 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
½ 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
LM4902 turns on. The slower the LM4902's outputs ramp to their quiescent DC voltage (nominally ½ VDD), the
smaller the turn-on pop. Choosing CB equal to 1.0 μF along with a small value of Ci (in the range of 0.1μF to
0.39μF), should produce a 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 or larger is recommended in all but the most cost sensitive
designs.
AUDIO POWER AMPLIFIER DESIGN
Design a 300 mW/8Ω Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
300mWrms
8Ω
1Vrms
Input Impedance
Bandwidth
20kΩ
100Hz–20 kHz ± 0.25dB
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 the Typical 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 5 and add the dropout voltage. Using this method, the minimum supply voltage would be (Vopeak
+ (2*VOD)), where VOD is extrapolated from the Dropout Voltage vs Supply Voltage curve in the Typical
Performance Characteristics section.
(5)
Using the Output Power vs Supply Voltage graph for an 8Ω load, the minimum supply rail is 3.5V. But since 5V is
a standard supply voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates
headroom that allows the LM4902 to reproduce peaks in excess of 700 mW 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 6.
(6)
RF/Ri = AVD/2
(7)
From Equation 6, the minimum AVD is 1.55; use AVD = 2.
Since the desired input impedance was 20 kΩ, and with a AVD of 2, a ratio of 1:1 of RF to Ri results in an
allocation of Ri = RF = 20 kΩ. The final design step is to address the bandwidth requirements which must be
stated as a pair of −3 dB frequency points. Five times away from a pole gives 0.17 dB down from passband
response which is better than the required ±0.25 dB specified.
fL = 100Hz/5 = 20Hz
(8)
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
17
Product Folder Links: LM4902
LM4902
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
www.ti.com
fH = 20kHz × 5 = 100kHz
(9)
As stated in the External Components Description section, Ri in conjunction with Ci create a highpass filter.
(10)
(11)
Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397μF; use 0.39μF
The high frequency pole is determined by the product of the desired high frequency pole, fH, and the differential
gain, AVD. With a AVD = 2 and fH = 100kHz, the resulting GBWP = 100kHz which is much smaller than the
LM4902 GBWP of 25MHz. This figure displays that if a designer has a need to design an amplifier with a higher
differential gain, the LM4902 can still be used without running into bandwidth problems.
DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4902
18
Submit Documentation Feedback
Copyright © 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4902
LM4902
www.ti.com
SNAS150D –DECEMBER 2001–REVISED APRIL 2013
REVISION HISTORY
Changes from Revision C (May 2013) to Revision D
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 18
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
19
Product Folder Links: LM4902
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status Package Type Package Pins Package
Eco Plan
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
Samples
Drawing
Qty
(1)
(2)
(3)
(4/5)
(6)
LM4902MM/NOPB
ACTIVE
VSSOP
DGK
8
1000 RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
GC3
(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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(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 finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material 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 MATERIALS INFORMATION
www.ti.com
29-Oct-2021
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)
LM4902MM/NOPB
VSSOP
DGK
8
1000
178.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
29-Oct-2021
*All dimensions are nominal
Device
Package Type Package Drawing Pins
VSSOP DGK
SPQ
Length (mm) Width (mm) Height (mm)
208.0 191.0 35.0
LM4902MM/NOPB
8
1000
Pack Materials-Page 2
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, regulatory or other requirements.
These resources are subject to change without notice. TI grants you permission to use these resources only for development of an
application that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license
is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you
will fully indemnify TI and its representatives against, any claims, damages, costs, losses, and liabilities arising out of your use of these
resources.
TI’s products are provided subject to TI’s Terms of Sale or other applicable terms available either on ti.com or provided in conjunction with
such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable warranties or warranty disclaimers for
TI products.
TI objects to and rejects any additional or different terms you may have proposed. IMPORTANT NOTICE
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2021, Texas Instruments Incorporated
相关型号：
©2020 ICPDF网 联系我们和版权申明