LM4894 1 Watt Fully Differential Audio Power Amplifier With

LM4894 1 Watt Fully Differential Audio Power Amplifier With
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LM4894
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LM4894
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1 Watt Fully Differential Audio Power Amplifier
With Shutdown Select
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FEATURES
1
•
•
2
•
•
•
•
•
Fully differential amplification
Available in space-saving packages micro
SMD, MSOP, and LLP
Ultra low current shutdown mode
Can drive capacitive loads up to 500pF
Improved pop and click circuitry eliminates
noises during turn-on and turn-off transitions
2.2 - 5.5V operation
No output coupling capacitors, snubber
networks or bootstrap capacitors required
•
•
•
•
Unity-gain stable
External gain configuration capability
Shutdown high or low selectivity
High CMRR
APPLICATIONS
•
•
•
Mobile phones
PDAs
Portable electronic devices
DESCRIPTION
The LM4894 is a fully differential audio power amplifier primarily designed for demanding applications in mobile
phones and other portable communication device applications. It is capable of delivering 1 watt of continuous
average power to an 8Ω BTL load with less than 1% distortion (THD+N) from a 5VDC power supply.
Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal
amount of external components. The LM4894 does not require output coupling capacitors or bootstrap
capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal
power consumption is a primary requirement.
The LM4894 features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by
either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables
the shutdown select pin to be driven in a likewise manner to enable Shutdown. Additionally, the LM4894 features
an internal thermal shutdown protection mechanism.
The LM4894 contains advanced pop and click circuitry which eliminates noises which would otherwise occur
during turn-on and turn-off transitions.
The LM4894 is unity-gain stable and can be configured by external gain-setting resistors.
Table 1. Key Specifications
VALUE
UNIT
■ Improved PSRR at 217Hz
80
dB(typ)
■ Power Output at 5.0V & 1% THD
1.0
W(typ)
■ Power Output at 3.3V & 1% THD
400
mW(typ)
■ Shutdown Current
0.1µA(typ)
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.
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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.
Mini Small Outline (MSOP) Package
Top View
LLP Package
Top View
9 Bump micro SMD Package
Top View
9 Bump micro SMD Package
Top View
2
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Typical Application
Figure 1. Typical Audio Amplifier Application Circuit
Absolute Maximum Ratings
(1)
Supply Voltage
6.0V
−65°C to +150°C
Storage Temperature
−0.3V to VDD +0.3V
Input Voltage
Power Dissipation
(2)
Internally Limited
ESD Susceptibility
(3)
2000V
ESD Susceptibility
(4)
200V
Junction Temperature
150°C
Thermal Resistance
θJC (LLP)
12°C/W
θJA (LLP)
63°C/W
θJA (micro SMD)
220°C/W
θJC (MSOP)
56°C/W
θJA (MSOP)
190°C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale Package."
See AN-1187 "Leadless Leadframe Package (LLP)."
(1)
(2)
(3)
(4)
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 specify performance limits. Electrical Characteristics state DC and AC electrical specifications
under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating
Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of
device performance.
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 LM4894, see power derating currents for additional information.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF–240pF discharged through all pins.
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Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ 85°C
2.2V ≤ VDD ≤ 5.5V
Supply Voltage
Electrical Characteristics VDD = 5V
(1) (2)
The following specifications apply for VDD = 5V, AV = 1, and 8Ω load unless otherwise specified. Limits apply for TA = 25°C.
LM4894
Symbol
Parameter
Conditions
Typical
Limit
(3)
(4)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, Io = 0A
4
8
mA (max)
ISD
Shutdown Current
Vshutdown = GND
0.1
1
µA (max)
Po
Output Power
THD = 1% (max); f = 1 kHz
LM4894LD, RL= 4Ω
0.1
%
87
dB (min)
Total Harmonic Distortion+Noise
Po = 0.4 Wrms; f = 1kHz
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
f = 217Hz
f = 1kHz
f = 1kHz
(3)
(4)
(5)
(6)
(7)
4
(6)
(6)
f = 217Hz
(1)
(2)
W (min)
1
PSRR
Common_Mode Rejection Ratio
1.4
LM4894, RL= 8Ω
THD+N
CMRR
(5)
(7)
(7)
f = 217Hz
0.850
83
83
63
80
50
dB
All voltages are measured with respect to the ground pin, unless otherwise specified.
For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
Typicals are measured at 25°C and represent the parametric norm.
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
When driving 4Ω loads from a 5V supply, the LM4894LD must be mounted to a circuit board.
Unterminated input.
10Ω terminated input.
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Electrical Characteristics VDD = 3V
(1) (2)
The following specifications apply for VDD = 3V, AV = 1, and 8Ω load unless otherwise specified. Limits apply for TA = 25°C.
LM4894
Symbol
Parameter
Conditions
Typical
(3)
Limit
(4)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, Io = 0A
3.5
6
mA (max)
ISD
Shutdown Current
Vshutdown = GND
0.1
1
µA (max)
Po
Output Power
THD = 1% (max); f = 1kHz
0.35
W
THD+N
Total Harmonic Distortion+Noise
Po = 0.25Wrms; f = 1kHz
0.325
%
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
87
dB
f = 217Hz
f = 1kHz
f = 217Hz
f = 1kHz
CMRR
(1)
(2)
(3)
(4)
(5)
(6)
Common-Mode Rejection Ratio
(5)
(5)
83
(6)
(6)
80
78
f = 217Hz
49
dB
All voltages are measured with respect to the ground pin, unless otherwise specified.
For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
Typicals are measured at 25°C and represent the parametric norm.
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
Unterminated input.
10Ω terminated input.
External Components Description
(Figure 1)
Components
1.
Functional Description
Ri
Inverting input resistance which sets the closed-loop gain in conjunction with Rf.
2.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
3.
CS
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.
4.
CB
Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External
Components, for information concerning proper placement and selection of CB.
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Typical Performance Characteristics
LD Specific Characteristics
6
LM4894LD
THD+N
vs
Output Power
VDD = 5V, 4Ω RL
LM4894LD
THD+N
vs
Frequency
VDD = 5V, 4Ω RL, and Power = 1W
LM4894LD
Power Dissipation vs
Output Power
LM4894LD
Power Derating Curve
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Typical Performance Characteristics
Non-LD Specific Characteristics
THD+N
vs
Frequency
at VDD = 5V, 8Ω RL, and PWR = 400mW
THD+N
vs
Frequency
at VDD = 3V, 8Ω RL, and PWR = 250mW
THD+N
vs
Frequency
at VDD = 3V, 4Ω RL, and PWR = 225mW
THD+N
vs
Frequency
at VDD = 2.6V, 8Ω RL, and PWR = 150mW
THD+N
vs
Frequency
at VDD = 2.6V, 4Ω RL, and PWR = 150mW
THD+N
vs
Output Power
at VDD = 5V, 8Ω RL
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Typical Performance Characteristics
Non-LD Specific Characteristics (continued)
8
THD+N
vs
Output Power
at VDD = 3V, 8Ω RL
THD+N
vs
Output Power
at VDD = 3V, 4Ω RL
THD+N
vs
Output Power
at VDD = 2.6V, 8Ω RL
THD+N
vs
Output Power
at VDD = 2.6V, 4Ω RL
Power Supply Rejection Ratio (PSRR) at VDD = 5V
Input 10Ω Terminated
Power Supply Rejection Ratio (PSRR) at VDD = 5V
Input Floating
Power Supply Rejection Ratio (PSRR) at VDD = 3V
Input 10Ω Terminated
Power Supply Rejection Ratio (PSRR) at VDD = 3V
Input Floating
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Typical Performance Characteristics
Non-LD Specific Characteristics (continued)
Output Power vs
Supply Voltage
Output Power vs
Supply Voltage
Power Dissipation vs
Output Power
Power Dissipation vs
Output Power
Power Dissipation vs
Output Power
Output Power vs
Load Resistance
Supply Current
vs
Shutdown Voltage
Shutdown Low
Supply Current
vs
Shutdown Voltage
Shutdown High
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Typical Performance Characteristics
Non-LD Specific Characteristics (continued)
10
Clipping (Dropout) Voltage vs
Supply Voltage
Open Loop Frequency Response
Power Derating Curve
Noise Floor
Input CMRR vs
Frequency
Input CMRR
vs
Frequency
PSRR vs
DC Common-Mode Voltage
PSRR
vs
DC Common-Mode Voltage
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Typical Performance Characteristics
Non-LD Specific Characteristics (continued)
THD
vs
Common-Mode Voltage
THD vs
Common-Mode Voltage
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APPLICATION INFORMATION
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4894 is a fully differential audio amplifier that features differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a common mode feedback amplifier that adjusts the
output voltages so that the average value remains VDD/2. When setting the differential gain, the amplifier can be
considered to have "halves". Each half uses an input and feedback resistor (Ri1and RF1) to set its respective
closed-loop gain (see Figure 1). With Ri1 = Ri2 and RF1 = RF2, the gain is set at -RF/Ri for each half. This results
in a differential gain of
AVD = -RF/Ri
(1)
It is extremely important to match the input resistors to each other, as well as the feedback resistors to each
other for best amplifier performance. See the Proper Selection of External Components section for more
information. A differential amplifier works in a manner where the difference between the two input signals is
amplified. In most applications, this would require input signals that are 180° out of phase with each other. The
LM4894 can be used, however, as a single ended input amplifier while still retaining its fully differential benefits.
In fact, completely unrelated signals may be placed on the input pins. The LM4894 simply amplifies the
difference between them. Figure 2 and Figure 3 show single-ended applications of the LM4894 that still take
advantage of the differential nature of the amplifier and the benefits to PSRR, common-mode noise reduction,
and "click and pop" reduction.
All of these applications, either single-ended or fully differential, provide what is known as a "bridged mode"
output (bridge-tied-load, BTL). This results in output signals at Vo1 and Vo2 that are 180° out of phase with
respect to each other. Bridged mode operation is different from the single-ended amplifier configuration that
connects the load between the amplifier output and ground. A bridged amplifier design has distinct advantages
over the single-ended configuration: it provides differential drive to the load, thus doubling maximum possible
output swing for a specific supply voltage. Four times the output power is possible compared with 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 excess clipping,
please refer to the Audio Power Amplifier Design section.
A bridged configuration, such as the one used in the LM4894, also creates a second advantage over singleended amplifiers. Since the differential outputs, Vo1 and VO2, are biased at half-supply, no net DC voltage exists
across the load. This assumes that the input resistor pair and the feedback resistor pair are properly matched
(see Proper Selection of External Components). BTL configuration eliminates the output coupling capacitor
required in single-supply, single-ended amplifier configurations. If an output coupling capacitor is not used in a
single-ended output configuration, the half-supply bias across the load would result in both increased internal IC
power dissipation as well as permanent loudspeaker damage. Further advantages of bridged mode operation
specific to fully differential amplifiers like the LM4894 include increased power supply rejection ratio, commonmode noise reduction, and click and pop reduction.
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS
The LM4894's exposed-DAP (die attach paddle) package (LD) provide 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, finally, surrounding air. The result is a low voltage audio
power amplifier that produces 1.4W 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 LM4894'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 and 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 (2 x 2) vias. The via diameter should be 0.012in - 0.013in with a 0.050in pitch. Ensure efficient thermal
conductivity by plating-through and solder-filling the vias.
12
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Best thermal performance is achieved with the largest practical copper heat sink area. If the heatsink and
amplifier share the same PCB layer, a nominal 2.5in2 (min) area is necessary for 5V operation with a 4Ω load.
Heatsink areas not placed on the same PCB layer as the LM4894 should be 5in2 (min) for the same supply
voltage and load resistance. The last two area recommendations apply for 25°C ambient temperature. In all
circumstances and conditions, the junction temperature must be held below 150°C to prevent activating the
LM4894's thermal shutdown protection. The LM4894's power de-rating curve in the Typical Performance
Characteristics shows the maximum power dissipation versus temperature. Example PCB layouts for the
exposed-DAP TSSOP and LLP packages are shown in the Demonstration Board Layout section. Further detailed
and specific information concerning PCB layout, fabrication, and mounting an LLP package is available from
National Semiconductor's package Engineering Group under application note AN1187.
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 de-pendent 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 1.4W to 1.37W. 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 sup-ply regulation. Therefore, making the power supply traces as wide as possible helps
maintain full output voltage swing.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifer, whether the amplifier is bridged or
single-ended. Equation 2 states the maximum power dissipation point for a single-ended 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 versus a single-ended amplifier operating at the same conditions.
PDMAX = 4 x (VDD)2/(2π2RL) Bridge Mode
(3)
Since the LM4894 has bridged outputs, the maximum internal power dissipation is 4 times that of a single-ended
amplifier. Even with this substantial increase in power dissipation, the LM4894 does not require additional
heatsinking under most operating conditions and output loading. From Equation 3, assuming a 5V power supply
and an 8Ω load, the maximum power dissipation point is 625mW. The maximum power dissipation point obtained
from Equation 3 must not be greater than the power dissipation results from Equation 4:
PDMAX = (TJMAX - TA)/θJA
(4)
The LM4894's θJA in an MUA10A package is 190°C/W. 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 higher power dissipation. For the typical application
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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. Recall that internal power dissipation is a function of output power. If typical operation is
not around the maximum power dissipation point, the LM4894 can operate at higher ambient temperatures.
Refer to the Typical Performance Characteristics curves for power dissipation information.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor location on both the bypass and power supply pins should be as close to
the device as possible. A larger half-supply bypass capacitor improves PSRR because it increases half-supply
stability. Typical applications employ a 5V regulator with 10µF and 0.1µF bypass capacitors that increase supply
stability. This, however, does not eliminate the need for bypassing the supply nodes of the LM4894. Although the
LM4894 will operate without the bypass capacitor CB, although the PSRR may decrease. A 1µF capacitor is
recommended for CB. This value maximizes PSRR performance. Lesser values may be used, but PSRR
decreases at frequencies below 1kHz. The issue of CB selection is thus dependant upon desired PSRR and click
and pop performance as explained in the section Proper Selection of External Components.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4894 contains shutdown circuitry that is used to
turn off the amplifier's bias circuitry. In addition, the LM4894 contains a Shutdown Mode pin, allowing the
designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level
logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply
be tied permanently to either VDD or GND to set the LM4894 as either a "shutdown-high" device or a "shutdownlow" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown Select
pin to the same state as the Shutdown Mode pin. For simplicity's sake, this is called "shutdown same", as the
LM4894 enters shutdown mode whenever the two pins are in the same logic state. The trigger point for either
shutdown high or shutdown low is shown as a typical value in the Supply Current vs Shutdown Voltage graphs in
the Typical Performance Characteristics section. It is best to switch between ground and supply for maximum
performance. While the device may be disabled with shutdown voltages in between ground and supply, 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 to shutdown. Another solution is to use a single-throw switch in conjunction
with an external pull-up resistor (or pull-down, depending on shutdown high or low application). This scheme
guarantees 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 when
optimizing device and system performance. Although the LM4894 is tolerant to a variety of external component
combinations, consideration of component values must be made when maximizing overall system quality.
The LM4894 is unity-gain stable, giving the designer maximum system flexibility. The LM4894 should be used in
low closed-loop gain configurations to minimize THD+N values and maximize signal to noise ratio. Low gain
configurations require large input signals to obtain a given output power. Input signals equal to or greater than
1Vrms are available from sources such as audio codecs. Please refer to the Audio Power Amplifier Design
section for a more complete explanation of proper gain selection. When used in its typical application as a fully
differential power amplifier the LM4894 does not require input coupling capacitors for input sources with DC
common-mode voltages of less than VDD. Exact allowable input common-mode voltage levels are actually a
function of VDD, Ri, and Rf and may be determined by Equation 5:
14
VCMi<(VDD-1.2)*((Rf+(Ri)/(Rf)-VDD*(Ri/2Rf)
(5)
VCMi<(VDD-1.2)*((Rf+(Ri)/(Rf)-VDD*(Ri/2Rf)
(6)
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Special care must be taken to match the values of the feedback resistors (RF1 and RF2) to each other as well as
matching the input resistors (Ri1 and Ri2) to each other (see Typical Application) more infront. Because of the
balanced nature of differential amplifiers, resistor matching differences can result in net DC currents across the
load. This DC current can increase power consumption, internal IC power dissipation, reduce PSRR, and
possibly damaging the loudspeaker. The chart below demonstrates this problem by showing the effects of
differing values between the feedback resistors while assuming that the input resistors are perfectly matched.
The results below apply to the application circuit shown in Typical Application, and assumes that VDD = 5V, RL =
8Ω, and the system has DC coupled inputs tied to ground.
Tolerance
RF1
RF2
V02 - V01
ILOAD
20%
0.8R
1.2R
-0.500V
62.5mA
10%
0.9R
1.1R
-0.250V
31.25mA
5%
0.95R
1.05R
-0.125V
15.63mA
1%
0.99R
1.01R
-0.025V
3.125mA
0%
R
R
0
0
Similar results would occur if the input resistors were not carefully matched. Adding input coupling capacitors in
between the signal source and the input resistors will eliminate this problem, however, to achieve best
performance with minimum component count it is highly recommended that both the feedback and input resistors
matched to 1% tolerance or better.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8Ω Audio Amplifier
Given:
Power Output
1Wrms
Load Impedance
8Ω
Input Level
1Vrms
Input Impedance
20kΩ
Bandwidth
–20kHz ± 0.25dB
A designer must first determine the minimum supply rail to obtain the specified output power. The supply rail can
be found by extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance
Characteristics section. A second way to determine the minimum supply rail is to calculate the required
VOPEAK using Equation 7 and add the dropout voltages. Using this method, the minimum supply voltage is
(Vopeak +(VDO TOP+(VDO BOT )), where VDO BOT and VDO TOP are extrapolated from the Dropout Voltage vs Supply
Voltage curve in the Typical Performance Characteristics section.
(7)
Using the Output Power vs Supply Voltage graph for an 8W load, the minimum supply rail just about 5V. Extra
supply voltage creates headroom that allows the LM4894 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 7.
(8)
Rf / Ri = AVD
From Equation 7, the minimum AVD is 2.83. Since the desired input impedance was 20kΩ, a ratio of 2.83:1 of Rf
to Ri results in an allocation of Ri = 20kΩ for both input resistors and Rf= 60kΩ for both feedback resistors. The
final design step is to address the bandwidth requirement which must be stated as a single -3dB frequency point.
Five times away from a -3dB point is 0.17dB down from passband response which is better than the required
±0.25dB specified.
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Product Folder Links: LM4894
15
NRND
LM4894
SNAS134H – MAY 2004 – REVISED OCTOBER 2011
www.ti.com
fH = 20kHz x 5 =100kHz
The high frequency pole is determined by the product of the desired frequency pole, fH , and the differential gain,
AVD . With a AVD = 2.83 and fH = 100kHz, the resulting GBWP = 150kHz which is much smaller than the LM4894
GBWP of 10MHz. This figure displays that if a designer has a need to design an amplifier with a higher
differential gain, the LM4894 can still be used without running into bandwidth limitations.
Figure 2. Single-Ended Input, "Shutdown-Low" Configuration
16
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Copyright © 2004–2011, Texas Instruments Incorporated
Product Folder Links: LM4894
NRND
LM4894
www.ti.com
SNAS134H – MAY 2004 – REVISED OCTOBER 2011
Figure 3. Single-Ended Input, "Shutdown-High" Configuration
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Copyright © 2004–2011, Texas Instruments Incorporated
Product Folder Links: LM4894
17
PACKAGE OPTION ADDENDUM
www.ti.com
12-Jan-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM4894MMX/NOPB
NRND
Package Type Package Pins Package Qty
Drawing
VSSOP
DGS
10
3500
Eco Plan
Lead/Ball Finish
MSL Peak Temp
Samples
(3)
(Requires Login)
(2)
TBD
Call TI
Call TI
(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.
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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
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