LM4818 [TI]
具有关断模式的 350W 单声道、模拟输入 AB 类音频放大器;
| 型号： | LM4818 |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | 具有关断模式的 350W 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24页 (文件大小：1439K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM4818
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SNAS163B –APRIL 2002–REVISED MAY 2013
LM4818
350mW Audio Power Amplifier with Shutdown
Mode
Check for Samples: LM4818
1
FEATURES
DESCRIPTION
The LM4818 is a mono bridged power amplifier that
is capable of delivering 350mWRMS output power into
a 16Ω load or 300mWRMS output power into an 8Ω
load with 10% THD+N from a 5V power supply.
23
•
SOIC Surface Mount Packaging.
Switch On/Off Click Suppression.
Unity-Gain Stable.
•
•
•
Minimum External Components.
The LM4818 Boomer™ audio power amplifier is
designed specifically to provide high quality output
power and minimize PCB area with surface mount
APPLICATIONS
packaging and
a minimal amount of external
•
•
•
General Purpose Audio
components. Since the LM4818 does not require
output coupling capacitors, bootstrap capacitors or
snubber networks, it is optimally suited for low-power
portable applications.
Portable Electronic Devices
Information Appliances (IA)
KEY SPECIFICATIONS
The closed loop response of the unity-gain stable
LM4818 can be configured using external gain-setting
resistors. The device is available in SOIC package
type to suit various applications.
•
•
•
THD+N at 1kHz, 350mW Continuous Average
Output Power into 16Ω 10% (max)
THD+N at 1kHz, 300mW Continuous Average
Output Power into 8Ω 10% (max)
Shutdown Current 0.7µA (typ)
Typical Application
Figure 1. Typical Audio Amplifier Application Circuit
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Boomer is a trademark of Texas Instruments.
2
3
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.
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LM4818
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Connection Diagram
Figure 2. SOIC Package - Top View
See Package Number D
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)(3)
Supply Voltage
6.0V
−65°C to +150°C
−0.3V to VDD +0.3V
Internally Limited
2.5kV
Storage Temperature
Input Voltage
Power Dissipation (PD)(4)
ESD Susceptibility(5)
ESD Susceptibility(6)
Junction Temperature (TJ)
Soldering Information
200V
150°C
Small Outline Package
Vapor Phase (60 seconds)
Infrared (15 seconds)
θJC (SOIC)
215°C
220°C
Thermal Resistance
35°C/W
θJA (SOIC)
170°C/W
(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's performance.
(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(4) 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. For the LM4818, TJMAX = 150°C and the typical junction-to-
ambient thermal resistance (θJA) when board mounted is 170°C/W for the SOIC package.
(5) Human body model, 100pF discharged through a 1.5 kΩ resistor.
(6) Machine Model, 220pF–240pF capacitor is discharged through all pins.
OPERATING RATINGS(1)(2)
Temperature Range TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ 85°C
2.0V ≤ VCC ≤ 5.5V
Supply Voltage
(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's performance.
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ELECTRICAL CHARACTERISTICS VDD = 5V(1)(2)
The following specifications apply for VDD = 5V, RL = 16Ω unless otherwise stated. Limits apply for TA = 25°C.
LM4818
Units
(Limits)
Symbol
Parameter
Conditions
Typical(3)
Limit(4)(5)
IDD
Quiescent Power Supply Current
Shutdown Current
VIN = 0V, Io = 0A
1.5
3.0
mA (max)
µA (max)
V (min)
V (max)
mV (max)
mW
(6)
ISD
VPIN1 = VDD
1.0
5.0
ISDIH
ISDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
4.0
1.0
VIN = 0V
5
50
THD = 10%, fIN = 1kHz
350
300
1
PO
Output Power
THD = 10%, fIN = 1kHz, RL = 8Ω
PO = 270mWRMS, AVD = 2, fIN = 1kHz
mW
THD+N
Total Harmonic Distortion + Noise
%
(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's performance.
(3) Typical specifications are specified at 25°C and represent the parametric norm.
(4) Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by designs, test, or statistical analysis.
(6) The Shutdown pin (pin 1) should be driven as close as possible to VDD for minimum current in Shutdown Mode.
ELECTRICAL CHARACTERISTICS VDD = 3V(1)(2)
The following specifications apply for VDD = 3V and RL = 16Ω load unless otherwise stated. Limits apply to TA = 25°C.
LM4818
Typical(3)
Units
(Limits)
Symbol
Parameter
Conditions
Limit(4)(5)
3.0
IDD
Quiescent Power Supply Current
Shutdown Current
VIN = 0V, Io = 0A
1.0
0.7
mA (max)
µA (max)
V (min)
V (max)
mV
(6)
ISD
VPIN1 = VDD
5.0
ISDIH
ISDIL
VOS
Shutdown Voltage Input High
Shutdown Voltage Input Low
Output Offset Voltage
2.4
0.6
VIN = 0V
5
110
90
1
50
THD = 10%, fIN = 1kHz
mW
PO
Output Power
THD = 10%, fIN = 1kHz, RL = 8Ω
PO = 80mWRMS, AVD = 2, fIN = 1kHz
mW
THD+N
Total Harmonic Distortion + Noise
%
(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's performance.
(3) Typical specifications are specified at 25°C and represent the parametric norm.
(4) Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by designs, test, or statistical analysis.
(6) The Shutdown pin (pin 1) should be driven as close as possible to VDD for minimum current in Shutdown Mode.
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EXTERNAL COMPONENTS DESCRIPTION
(Figure 1)
Components
Functional Description
1.
Ri
Combined with Rf, this inverting input resistor sets the closed-loop gain. Ri also forms a high pass filter with Ci at fc =
1/(2πRiCi).
2.
Ci
This input coupling capacitor blocks DC voltage at the amplifier's terminals. Combined with Ri, it creates a high pass
filter with Ri at fc = 1/(2πRiCi). Refer to the section, PROPER SELECTION OF EXTERNAL COMPONENTS for an
explanation of how to determine the value of Ci.
3.
4.
Rf
Combined with Ri, this is the feedback resistor that sets the closed-loop gain: Av = 2(RF/Ri).
CS
This is the power supply bypass capacitor that filters the voltage applied to the power supply pin. Refer to the
APPLICATION INFORMATION section for proper placement and selection of Cs.
5.
6.
CB
This is the bypass pin capacitor that filters the voltage at the BYPASS pin. Refer to the section, PROPER SELECTION
OF EXTERNAL COMPONENTS for information concerning proper placement and selection of CB.
CB2
This is an optional capacitor that is not needed in the majority of applications. If the capacitor is not used, pin 3 should
be connected directly to pin2. Refer to the section PROPER SELECTION OF EXTERNAL COMPONENTS for more
information concerning CB2
.
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TYPICAL PERFORMANCE CHARACTERISTICS
Figure 3.
Figure 5.
Figure 7.
Figure 4.
Figure 6.
Figure 8.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Output Power vs Supply Voltage
Output Power vs Supply Voltage
RL = 8Ω
RL = 16Ω
Figure 15.
Figure 16.
Output Power vs Supply Voltage
RL = 32Ω
Output Power vs Load Resistance
Figure 17.
Figure 18.
Power Dissipation vs
Output Power
VDD = 5V
Power Dissipation vs
Output Power
VDD = 3V
Figure 19.
Figure 20.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Frequency Response vs
Input Capacitor Size
Power Derating Curves
Figure 21.
Figure 22.
Supply Current vs
Supply Voltage
Figure 23.
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APPLICATION INFORMATION
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4818 consist of two operational amplifiers. External resistors, Ri and RF set the
closed-loop gain of the first amplifier (and the amplifier overall), whereas two internal 20kΩ resistors set the
second amplifier's gain at -1. The LM4818 is typically used to drive a speaker connected between the two
amplifier outputs.
Figure 1 shows that the output of Amp1 servers as the input to Amp2, which results in both amplifiers producing
signals identical in magnitude but 180° out of phase. Taking advantage of this phase difference, a load is placed
between V01 and V02 and driven differentially (commonly referred to as "bridge mode"). This results in a
differential gain of
AVD= 2 *(Rf/Ri)
(1)
Bridge mode is different from single-ended amplifiers that drive loads connected between a single amplifier's
output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-ended
configuration: its differential output doubles the voltage swing across the load. This results in four times the
output power when compared to a single-ended amplifier under the same conditions. This increase in attainable
output assumes that the amplifier is not current limited or the output signal is not clipped. To ensure minimum
output signal clipping when choosing an amplifier's closed-loop gain, refer to the AUDIO POWER AMPLIFIER
DESIGN EXAMPLE section.
Another advantage of the differential bridge output is no net DC voltage across the load. This results from biasing
V01 and V02 at half-supply. 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 may permanently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful bridged or single-ended amplifier. Equation 2
states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and
driving a specified load.
PDMAX = (VDD)2 /(2π2RL ) (W) Single-ended
(2)
However, a direct consequence of the increased power delivered to the load by a bridged amplifier is an increase
in the internal power dissipation point for a bridge amplifier operating at the same given conditions. Equation 3
states the maximum power dissipation point for a bridged amplifier operating at a given supply voltage and
driving a specified load.
PDMAX = 4(VDD)2/(2π2 RL ) (W) Bridge Mode
(3)
The LM4818 has two operational amplifiers in one package and the maximum internal power dissipation is four
times that of a single-ended amplifier. However, even with this substantial increase in power dissipation, the
LM4818 does not require heatsinking. From Equation 3, assuming a 5V power supply and an 8Ω load, the
maximum power dissipation point is 633mW. The maximum power dissipation point obtained from Equation 3
must not exceed the power dissipation predicted by Equation 4:
PDMAX = (TJMAX - TA)/θJA (W)
(4)
For the D package, θJA = 170°C/W and TJMAX = 150°C for the LM4818. For a given ambient temperature, TA,
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 the result of Equation 4, then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. For a typical application using the D packaged LM4818 with a
5V power supply and an 8Ω load, the maximum ambient temperature that does not violate the maximum junction
temperature is approximately 42°C. It is assumed that a device is a surface mount part operating around the
maximum power dissipation point. The assumption that the device is operating around the maximum power
dissipation point is incorrect for an 8Ω load. The maximum power dissipation point occurs when the output power
is equal to the maximum power dissipation or 50% efficiency. The LM4818 is not capable of the output power
level (633mW) required to operate at the maximum power dissipation point for an 8Ω load. To find the maximum
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power dissipation, the graph Figure 20 must be used. From the graph, the maximum power dissipation for an 8Ω
load and a 5V supply is approximately 575mW. Substituting this value back into Equation 4 for PDMAX and using
θJA = 170°C/W for the D package, the maximum ambient temperature is 52°C. Refer to the TYPICAL
PERFORMANCE CHARACTERISTICS curves for power dissipation information for lower output powers and
maximum power dissipation for each package at a given ambient temperature.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. The capacitors connected to the bypass and power supply pins should be placed as close to the
LM4818 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
value increases. Typical applications employ a 5V regulator with 10µF and 0.1µF filter capacitors that aid in
supply stability. Their presence, however, does not eliminate the need for bypassing the supply nodes of the
LM4818. The selection of bypass capacitor values, especially CB , depends on desired PSRR requirements, click
and pop performance as explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS, as
well as system cost and size constraints.
SHUTDOWN FUNCTION
The voltage applied to the LM4818's SHUTDOWN pin controls the shutdown function. Activate micro-power
shutdown by applying VDD to the SHUTDOWN pin. When active, the LM4818's micro-power shutdown feature
turns off the amplifier's bias circuitry, reducing the supply current. The logic threshold is typically 1/2VDD. The low
0.7µA typical shutdown current is achieved by applying a voltage that is as near as VDD as possible to the
SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. Avoid intermittent or
unexpected micro-power shutdown by ensuring that the SHUTDOWN pin is not left floating but connected to
either VDD or GND.
There are a few ways to activate micro-power shutdown. These included using a single-pole, single-throw switch,
a microcontroller, or a microprocessor. When using a switch, connect an external 10kΩ to 100kΩ pull-up resistor
between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select
normal amplifier operation by closing the switch. Opening the switch connects the shutdown pin to VDD through
the pull-up resistor, activating micro-power shutdown. The switch and resistor ensure that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a system with a microprocessor or a microcontroller, use
a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active
circuitry eliminates the pull-up resistor
PROPER SELECTION OF EXTERNAL COMPONENTS
Optimizing the LM4818's performance requires properly selecting external components. Though the LM4818
operates well when using external components with wide tolerances, best performance is achieved by optimizing
component values.
The LM4818 is unity gain stable, giving the designer maximum design flexibility. The gain should be set to no
more than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum
signal-to-noise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain
demands input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal
sources such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the AUDIO POWER
AMPLIFIER DESIGN EXAMPLE section for more information on selecting the proper gain.
Another important consideration is the amplifier's close-loop bandwidth. 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 that limits low frequency response. This value should be chosen based on needed
frequency response for a few distinct reasons discussed below
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires a high value input coupling capacitor (Ci in Figure 1). A high
value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases the
speakers used in portable systems, whether internal or external, have little ability to reproduce signals below
150Hz. Applications using speakers with limited frequency response reap little improvement by using a large
input capacitor.
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Besides affecting system cost and size, Ci has an effect on the LM4818's click and pop performance. When the
supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero
to a quiescent state. The magnitude of the pop is directly proportional to the input capacitor's value. Higher value
capacitors need more time to reach a quiescent DC voltage (usually 1/2 VDD) when charged with a fixed current.
The amplifier's output charges the input capacitor through the feedback resistor, RF. Thus, selecting an input
capacitor value that is no higher than necessary to meet the desired -3dB frequency can minimize pops.
As shown in Figure 1, the input resistor (Ri) and the input capacitor, Ci produce a -3dB high pass filter cutoff
frequency that is found using Equation 5.
f-3dB = 1/(2 πRiCi) (Hz)
(5)
As an example when using a speaker with a low frequency limit of 150Hz, Ci, using Equation 5 is 0.063µF. The
0.39µF Ci shown in Figure 1 allows the LM4818 to drive a high efficiency, full range speaker whose response
extends down to 20Hz.
Besides optimizing the input capacitor value, the bypass capacitor value, CB requires careful consideration. The
bypass capacitor's value is the most critical to minimizing turn-on pops because it determines how fast the
LM4818 turns on. The slower the LM4818's outputs ramp to their quiescent DC voltage (nominally 1/2VDD), the
smaller the turn-on pop. While the device will function properly (no oscillations or motorboating), with CB less
than 1.0µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to or
greater than 1.0µF is recommended in all but the most cost sensitive designs.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consideration should be paid to the value of CB, the capacitor
connected to the BYPASS pin. Since CB determines how fast the LM4818 settles to quiescent operation, its
value is critical when minimizing turn-on pops. The slower the LM4818's outputs ramp to their quiescent DC
voltage (nominally 1/2VDD), 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) produces a click-less and pop-less shutdown function. As discussed above,
choosing Ci no larger than necessary for the desired bandwidth helps minimize clicks and pops. If using the
optional capacitor, CB2, the total capacitance see at the BYPASS pin is CB + CB2. When using the values shown
in Figure 1 for CB and CB2 the change in the capacitance seen by the BYPASS pin is not significant relative to
capacitor value tolerances.
Optimizing Click and Pop Reduction Performance
The LM4818 contains circuitry that minimizes turn-on and shutdown transients or "clicks and pops". For this
discussion, turn on refers to either applying the power or supply voltage or when the shutdown mode is
deactivated. While the power supply is ramping to it's final value, the LM4818's internal amplifiers are configured
as unity gain buffers. An internal current source charges the voltage of the bypass capacitor, CB, connected to
the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track the voltage charging on the
bypass capacitor. The gain of the internal amplifiers remains unity until the bypass capacitor is fully charged to
1/2VDD. As soon as the voltage on the bypass capacitor is stable, the device becomes fully operational. Although
the BYPASS pin current cannot be modified, changing the size of the bypass capacitor, CB, alters the device's
turn-on time and magnitude of "clicks and pops". Increasing the value of CB reduces the magnitude of turn-on
pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time (Ton) increases. There is a
linear relationship between the size of CB and the turn on time. If using the optional capacitor, CB2, the total
capacitance see at the BYPASS pin is CB and CB2. The total capacitance see at the BYPASS pin must be
considered for the table below and when optimizing click and pop performance. Below are some typical turn-on
times for various values of CB:
CB
TON
20ms
200ms
440ms
940ms
2S
0.01µF
0.1µF
0.22µF
0.47µF
1.0µF
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In order to eliminate "clicks and pops", all capacitors must be discharged before turn-on. Rapidly switching VDD
may not allow the capacitors to fully discharge, which may cause "clicks and pops".
AUDIO POWER AMPLIFIER DESIGN EXAMPLE
The following are the desired operational parameters:
Given:
Power Output
Load Impedance
Input Level
100mW
16Ω
1Vrms (max)
20kΩ
Input Impedance
Bandwidth
100Hz–20kHz ± 0.25dB
The design begins by specifying the minimum supply voltage necessary to obtain the specified output power. To
find this minimum supply voltage, use the Output Power vs. Supply Voltage graph in the TYPICAL
PERFORMANCE CHARACTERISTICS section. From the graph for a 16Ω load, (graphs are for 8Ω, 16Ω, and
32Ω loads) the supply voltage for 100mW of output power with 1% THD+N is approximately 3.15 volts.
Additional supply voltage creates the benefit of increased headroom that allows the LM4818 to reproduce peaks
in excess of 100mW without output signal clipping or audible distortion. The choice of supply voltage must also
not create a situation that violates maximum dissipation as explained above in the Power Dissipation section. For
example, if a 3.3V supply is chosen for extra headroom then according to Equation 3 the maximum power
dissipation point with a 16Ω load is 138mW. Using Equation 4 the maximum ambient temperature is 126°C for
the D package.
After satisfying the LM4818's power dissipation requirements, the minimum differential gain is found using
Equation 6.
(6)
Thus a minimum gain of 1.27 V/V allows the LM4818 to reach full output swing and maintain low noise and
THD+N performance. For this example, let AVD = 1.27. The amplifier's overall gain is set using the input (Ri) and
feedback (RF) resistors. With the desired input impedance set to 20kΩ, the feedback resistor is found using
Equation 7.
RF/Ri = AVD/2 (V/V)
(7)
The value of RF is 13kΩ.
The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired
±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth
limit. The gain variation for both response limits is 0.17dB, well with in the ±0.25dB desired limit.
The results are:
fL = 100Hz/5 = 20Hz
(8)
(9)
fH = 20 kHz*5 = 100kHz
As mentioned in the PROPER SELECTION OF EXTERNAL COMPONENTS section, Ri and Ci create a high
pass filter that sets the amplifier's lower band pass frequency limit. Find the coupling capacitor's value using
Equation 10.
Ci ≥ 1/(2πRifc) (F)
(10)
Ci ≥ 0.398µF, a standard value of 0.39µF will be used. The product of the desired high frequency cutoff (100kHz
in this example) and the differential gain, AVD, determines the upper pass band response limit. With AVD = 1.27
and fH = 100kHz, the closed-loop gain bandwidth product (GBWP) is 127kHz. This is less than the LM4818's
900kHz GBWP. With this margin the amplifier can be used in designs that require more differential gain while
avoiding performance restricting bandwidth limitations.
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Figure 24. HIGHER GAIN AUDIO AMPLIFIER
The LM4818 is unity-gain stable and requires no external components besides gain-setting resistors, an input
coupling capacitor, and proper supply bypassing in the typical application. However, if a closed-loop differential
gain of greater than 10 is required, a feedback capacitor (C4) may be needed as shown in Figure 24 to
bandwidth limit the amplifier. This feedback capacitor creates a low pass filter that eliminates possible high
frequency oscillations. Care should be taken when calculating the -3dB frequency in that an incorrect
combination of R3 and C4 will cause rolloff before 20kHz. A typical combination of feedback resistor and
capacitor that will not produce audio band high frequency rolloff is R3 = 20kΩ and C4 = 25pF. These components
result in a -3dB point of approximately 320 kHz. It is not recommended that the feedback resistor and capacitor
be used to implement a band limiting filter below 100kHz.
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LM4818
SNAS163B –APRIL 2002–REVISED MAY 2013
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Figure 25. REFERENCE DESIGN BOARD and PCB LAYOUT GUIDELINES
LM4818 SOIC DEMO BOARD ARTWORK
Composite View
Silk Screen
14
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Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM4818
LM4818
www.ti.com
SNAS163B –APRIL 2002–REVISED MAY 2013
Top Layer
Bottom Layer
Table 1. Mono LM4818 Reference Design Boards
Bill of Material for all Demo Boards
Item
1
Part Number
Part Description
Qty
1
Ref Designator
551011208-001
482911183-001
151911207-001
151911207-002
152911207-001
472911207-001
210007039-002
LM4818 Mono Reference Design Board
LM4818 Audio AMP
10
20
21
25
30
35
1
U1
Tant Cap 1uF 16V 10
1
C1
Cer Cap 0.39uF 50V Z5U 20% 1210
Tant Cap 1uF 16V 10
1
C2
1
C3
Res 20K Ohm 1/10W 5
3
R1, R2, R3
J1
Jumper Header Vertical Mount 2X1 0.100
2
PCB LAYOUT GUIDELINES
This section provides practical guidelines for mixed signal PCB layout that involves various digital/analog power
and ground traces. Designers should note that these are only "rule-of-thumb" recommendations and the actual
results will depend heavily on the final layout.
General Mixed Signal Layout Recommendation
Power and Ground Circuits
For two layer mixed signal design, it is important to isolate the digital power and ground trace paths from the
analog power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central
point rather than daisy chaining traces together in a serial manner) can have a major impact on low level signal
performance. Star trace routing refers to using individual traces to feed power and ground to each circuit or even
device. This technique will take require a greater amount of design time but will not increase the final price of the
board. The only extra parts required will be some jumpers.
Single-Point Power / Ground Connections
The analog power traces should be connected to the digital traces through a single point (link). A "Pi-filter" can
be helpful in minimizing high frequency noise coupling between the analog and digital sections. It is further
recommended to put digital and analog power traces over the corresponding digital and analog ground traces to
minimize noise coupling.
Placement of Digital and Analog Components
All digital components and high-speed digital signals traces should be located as far away as possible from
analog components and circuit traces.
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Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB
layer. When traces must cross over each other do it at 90 degrees. Running digital and analog traces at 90
degrees to each other from the top to the bottom side as much as possible will minimize capacitive noise
coupling and cross talk.
16
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Product Folder Links: LM4818
LM4818
www.ti.com
SNAS163B –APRIL 2002–REVISED MAY 2013
REVISION HISTORY
Changes from Revision A (May 2013) to Revision B
Page
•
Changed layout of National Data Sheet to TI format .......................................................................................................... 16
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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)
LM4818MX/NOPB
ACTIVE
SOIC
D
8
2500 RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
LM48
18M
(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
8-May-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)
LM4818MX/NOPB
SOIC
D
8
2500
330.0
12.4
6.5
5.4
2.0
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
8-May-2013
*All dimensions are nominal
Device
Package Type Package Drawing Pins
SOIC
SPQ
Length (mm) Width (mm) Height (mm)
367.0 367.0 35.0
LM4818MX/NOPB
D
8
2500
Pack Materials-Page 2
PACKAGE OUTLINE
D0008A
SOIC - 1.75 mm max height
SCALE 2.800
SMALL OUTLINE INTEGRATED CIRCUIT
C
SEATING PLANE
.228-.244 TYP
[5.80-6.19]
.004 [0.1] C
A
PIN 1 ID AREA
6X .050
[1.27]
8
1
2X
.189-.197
[4.81-5.00]
NOTE 3
.150
[3.81]
4X (0 -15 )
4
5
8X .012-.020
[0.31-0.51]
B
.150-.157
[3.81-3.98]
NOTE 4
.069 MAX
[1.75]
.010 [0.25]
C A B
.005-.010 TYP
[0.13-0.25]
4X (0 -15 )
SEE DETAIL A
.010
[0.25]
.004-.010
[0.11-0.25]
0 - 8
.016-.050
[0.41-1.27]
DETAIL A
TYPICAL
(.041)
[1.04]
4214825/C 02/2019
NOTES:
1. Linear dimensions are in inches [millimeters]. Dimensions in parenthesis are for reference only. Controlling dimensions are in inches.
Dimensioning and tolerancing per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
exceed .006 [0.15] per side.
4. This dimension does not include interlead flash.
5. Reference JEDEC registration MS-012, variation AA.
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EXAMPLE BOARD LAYOUT
D0008A
SOIC - 1.75 mm max height
SMALL OUTLINE INTEGRATED CIRCUIT
8X (.061 )
[1.55]
SYMM
SEE
DETAILS
1
8
8X (.024)
[0.6]
SYMM
(R.002 ) TYP
[0.05]
5
4
6X (.050 )
[1.27]
(.213)
[5.4]
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE:8X
SOLDER MASK
OPENING
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
METAL
EXPOSED
METAL
EXPOSED
METAL
.0028 MAX
[0.07]
.0028 MIN
[0.07]
ALL AROUND
ALL AROUND
SOLDER MASK
DEFINED
NON SOLDER MASK
DEFINED
SOLDER MASK DETAILS
4214825/C 02/2019
NOTES: (continued)
6. Publication IPC-7351 may have alternate designs.
7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.
www.ti.com
EXAMPLE STENCIL DESIGN
D0008A
SOIC - 1.75 mm max height
SMALL OUTLINE INTEGRATED CIRCUIT
8X (.061 )
[1.55]
SYMM
1
8
8X (.024)
[0.6]
SYMM
(R.002 ) TYP
[0.05]
5
4
6X (.050 )
[1.27]
(.213)
[5.4]
SOLDER PASTE EXAMPLE
BASED ON .005 INCH [0.125 MM] THICK STENCIL
SCALE:8X
4214825/C 02/2019
NOTES: (continued)
8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
9. Board assembly site may have different recommendations for stencil design.
www.ti.com
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