LM4816MTX [NSC]
IC 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20, 4.40 MM, TSSOP-20, Audio/Video Amplifier;
| 型号： | LM4816MTX |
| 厂家： | 
National Semiconductor |
| 描述： | IC 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20, 4.40 MM, TSSOP-20, Audio/Video Amplifier 放大器 光电二极管 商用集成电路 |
| 文件： | 总13页 (文件大小：421K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
October 2003
LM4816
1W Stereo Audio Amplifier + Adjustable Output Limiter
General Description
Key Specifications
The LM4816 combines a bridged-connected (BTL) stereo
audio power amplifier with an adjustable output voltage mag-
nitude limiter. The audio amplifier delivers 1.0W to an 8Ω
load with less than 1.0% THD+N while operating on a 5V
power supply. With VLIM set to 1.0V, the amplifier outputs are
j
POUT (BTL):
VDD = 5V, THD = 1%, RL = 8Ω
Power supply range
Limiter adjustment range
Shutdown current
1.0W (typ)
3.0V to 5.5V
GND to VDD/2
0.06µA (typ)
j
j
j
clamped to 6Vp-p
,
800mV.
The LM4816 features an external controlled micropower
shutdown mode and thermal shutdown protection. It also
utilizes circuitry that reduces “clicks and pops” during device
turn-on and return from shutdown.
Features
n Stereo BTL amplifier
Boomer audio power amplifiers are designed specifically to
use few external components and provide high quality output
power in a surface mount package.
n Adjustable output voltage magnitude limiter
n “Click and pop” suppression circuitry
n Unity-gain stable audio amplifiers
n Thermal shutdown protection circuitry
n TSSOP (MT) package
Applications
n Notebook computers
n Multimedia monitors
n Desktop computers
n Portable televisions
Typical Application
20033201
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
DS200332
www.national.com
Connection Diagram
20033229
Top View
Order Number LM4816MT
See NS Package Number MTC20 for TSSOP
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2
Absolute Maximum Ratings (Note 1)
Vapor Phase (60 sec.)
215˚C
220˚C
Infrared (15 sec.)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
See AN-450 “Surface Mounting and their Effects on
Product Reliablilty” for other methods of soldering
surface mount devices.
Supply Voltage
Storage Temperature
Input Voltage
6.0V
−65˚C to +150˚C
−0.3V to VDD
+0.3V
Thermal Resistance
θJC (typ)—MTC20
θJA (typ)—MTC20
20˚C/W
80˚C/W
Power Dissipation (Note 2)
ESD Susceptibility(Note 3)
ESD Susceptibility (Note 4)
Junction Temperature
Internally limited
2000V
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage
200V
150˚C
−40˚C ≤ TA ≤ 85˚C
3.0V ≤ VDD ≤ 5.5V
Solder Information
Small Outline Package
Electrical Characteristics (Notes 1, 5)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25˚C.
Symbol
Parameter
Conditions
LM4816
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
VDD
Supply Voltage
3.0
5.5
15
5
V (min)
V (max)
Quiescent Power Supply
Current
mA (max)
mA (min)
µA (min)
IDD
ISD
VIN = 0V, IO = 0A (Note 8)
9.0
Shutdown Current
VDD applied to the
SHUTDOWN pin
0.06
2
VIH
VIL
Shutdown Logic High Input
Threshold Voltage
3.0
1.8
V (min)
V (max)
Shutdown Logic Low Input
Threshold Voltage
VOS
Output Offset Voltage
VIN = 0V
5
50
mV (max)
W (min)
THD+N = 1%, f = 1kHz, RL
=
1.0
0.9
8Ω
PO
Output Power (Note 9)
THD+N = 10%, f = 1kHz, RL
= 8Ω
1.5
0.03
6.0
W
%
20Hz ≤ f ≤ 20kHz, AVD = 2
RL = 8Ω, PO = 400mW
Total Harmonic Distortion +
Noise
THD+N
∞
, VIN =
VLIM = 1.0V, RL
4VP-P
=
VLIM
Limiter Clamp Voltage
5.2
6.8
VP-P (min)
VP-P (max)
VO P-P = (VOUT+ - VOUT-
)
PSRR
Power Supply Rejection
ratio
VDD = 5V, VRIPPLE
200VRMS
=
RL = 8Ω, CB = 1.0µF
Inputs Floating
67
43
90
98
dB
dB
dB
dB
Inputs terminated with 10Ω
XTALK
SNR
Channel Separation
Signal to Noise Ratio
f = 1kHz, CB = 1.0µF
VDD = 5V, PO = 1.0W, RL
=
8Ω
Note 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 guarantee specific 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.
Note 2: The maximum power dissipation is dictated by T
, θ , and the ambient temperature T and must be derated at elevated temperatures. The maximum
JMAX JA
A
allowable power dissipation is P
= (T
− T )/θ . For the LM4816, T
= 150˚C. For the θ s for different packages, please see the Application
DMAX
JMAX
A
JA
JMAX
JA
Information section or the Absolute Maximum Ratings section.
3
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Note 3: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 4: Machine model, 220pF–240pF discharged through all pins.
Note 5: All voltages are measured with respect to the ground (GND) pins unless otherwise specified.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 8: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
Note 9: Output power is measured at the device terminals.
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Output Power
20033267
20033299
VDD = 5V, RL = 8Ω, POUT = 150mW
VDD = 5V, RL = 8Ω, fIN = 1kHz
THD+N vs Frequency
THD+N vs Output Power
20033265
20033268
VDD = 3V, RL = 8Ω, POUT = 150mW
VDD = 3V, RL = 8Ω, fIN = 1kHz
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Typical Performance Characteristics (Continued)
THD+N vs Frequency
THD+N vs Output Power
20033266
20033295
VDD = 5.5V, RL = 8Ω, POUT = 150mW
VDD = 5.5V, RL = 8Ω, fIN = 1kHz
THD+N vs Output Power
PSRR vs Frequency
20033242
VDD = 5V, RL = 8Ω, RSOURCE = 10Ω,
20033264
VRIPPLE = 200mVP-P, at (from top to bottom at 500Hz):
CBYPASS = 0.1µF, CBYPASS = 1.0µF
VDD = 5V, RL = 8Ω, fIN = 1kHz,
at (from left to right at 7% THD+N):
VLIM = 2V, 1.9V, 1.8V, 1.7V, 1.6V, 1.5V, 1.0V, 0.5V, 0V
PSRR vs Frequency
PSRR vs Frequency
20033243
20033240
VDD = 3V, RL = 8Ω, RSOURCE = 10Ω,
∞
,
VDD = 5V, RL = 8Ω, RSOURCE
VRIPPLE = 200mVP-P, at (from top to bottom at 500Hz):
CBYPASS = 0.1µF, CBYPASS = 1.0µF
=
VRIPPLE = 200mVP-P, at (from top to bottom at 500Hz):
CBYPASS = 0.1µF, CBYPASS = 1.0µF
5
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Typical Performance Characteristics (Continued)
PSRR vs Frequency
Cross Talk
20033241
20033239
∞
VDD = 3V, RL = 8Ω, RSOURCE
=
,
VDD = 5V, RL = 8Ω, POUT = 150mW, at (from top to
bottom at 2kHz):
VRIPPLE = 200mVP-P, at (from top to bottom at 500Hz):
CBYPASS = 0.1µF, CBYPASS = 1.0µF
-N A driven, VOUTB measured;
-N B driven, VOUTA measured
Cross Talk
Cross Talk
20033237
VDD = 3V, RL = 8Ω, POUT = 150mW,
at (from top to bottom at 2kHz):
-N A driven, VOUTB measured;
-N B driven, VOUTA measured
20033238
VDD = 5.5V, RL = 8Ω, POUT = 150mW, at (from top to
bottom at 2kHz):
-N A driven, VOUTB measured;
-N B driven, VOUTA measured
Supply Current vs
Supply Voltage
Output Power vs
Supply Voltage
20033253
RL = 8Ω, VIN = 0V
RSOURCE = 50Ω
20033230
RL = 8Ω, fIN = 1kHz, at (from top to bottom at 4.6V):
THD+N = 10%, THD+N = 1%
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6
Typical Performance Characteristics (Continued)
Output Power vs
Load Resistance
Dropout Voltage vs
Supply Voltage
20033255
RL = 8Ω, fIN = 1kHz, at (from top to bottom at 4.5V):
20033257
VDD = 5V, fIN = 1kHz, at (from top to bottom at 32Ω):
THD+N = 10%, THD+N = 1%
positive signal swing, negative signal swing
Power Dissipation vs
Output Power
Power Derating Curve
20033256
20033252
VDD = 5V, fIN = 1kHz, at (from top to bottom at 0.20W):
RL = 8Ω, 16Ω, 32Ω
Open Loop
Frequency Response
20033222
7
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External Components Description
(Refer to Figure 1.)
Components
Functional Description
1.
Ri
The Inverting input resistance, along with Rf, set the closed-loop gain. Ri, along with Ci, form a high pass
filter with fc = 1/(2πRiCi).
2.
Ci
The input coupling capacitor blocks DC voltage at the amplifier’s input terminals. Ci, along with Ri, create a
highpass filter with fc = 1/(2πRiCi). Refer to the section, SELECTING PROPER EXTERNAL
COMPONENTS, for an explanation of determining the value of Ci.
3.
4.
Rf
The feedback resistance, along with Ri, set the closed-loop gain.
Cs
The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about
properly placing, and selecting the value of, this capacitor.
5.
CB
The capacitor, CB, filters the half-supply voltage present on the BYPASS pin. Refer to the SELECTING
PROPER EXTERNAL COMPONENTS section for information concerning proper placement and selecting
CB’s value.
Application Information
20033201
* Refer to the section Proper Selection of External Components, for a detailed discussion of C size.
B
FIGURE 1. Typical Audio Amplifier Application Circuit
Pin out shown for the LLP package. Refer to the Connection Diagrams for the pinout of the TSSOP package.
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8
The LM4816’s power dissipation is twice that given by Equa-
tion (2) or Equation (3) when operating in the single-ended
mode or bridge mode, respectively. Twice the maximum
power dissipation point given by Equation (3) must not ex-
ceed the power dissipation given by Equation (4):
Application Information (Continued)
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4816 consists of two pairs of
operational amplifiers, forming a two-channel (channel A and
channel B) stereo amplifier. (Though the following discusses
channel A, it applies equally to channel B.) External resistors
Rf and Ri set the closed-loop gain of Amp1A, whereas two
internal 20kΩ resistors set Amp2A’s gain at -1. The LM4816
drives a load, such as a speaker, connected between the two
amplifier outputs, -OUTA and +OUTA.
PDMAX’ = (TJMAX − TA) / θJA
(4)
The LM4816’s TJMAX = 150˚C. In the MT (TSSOP) package,
the LM4816’s θJA is 80˚C/W. At any given ambient tempera-
ture TJ\A, use Equation (4) to find the maximum internal
power dissipation supported by the IC packaging. Rearrang-
ing Equation (4) and substituting PDMAX for PDMAX’ results
in Equation (5). This equation gives the maximum ambient
temperature that still allows maximum stereo power dissipa-
tion without violating the LM4816’s maximum junction tem-
perature.
Figure 1 shows that Amp1A’s output serves as Amp2A’s
input. This results in both amplifiers producing signals iden-
tical in magnitude, but 180˚ out of phase. Taking advantage
of this phase difference, a load is placed between -OUTA
and +OUTA and driven differentially (commonly referred to
as "bridge mode"). This results in a differential gain of
AVD = 2 x (Rf / Ri)
(1)
TA = TJMAX − 2 x PDMAX θJA
(5)
Bridge mode amplifiers are different from single-ended am-
plifiers that drive loads connected between a single amplifi-
er’s output and ground. For a given supply voltage, bridge
mode has a distinct advantage over the single-ended con-
figuration: its differential output doubles the voltage swing
across the load. This produces four times the output power
when compared to a single-ended amplifier under the same
conditions. This increase in attainable output power as-
sumes that the amplifier is not current limited or that the
output signal is not clipped. To ensure minimum output sig-
nal clipping when choosing an amplifier’s closed-loop gain,
refer to the Audio Power Amplifier Design section.
For a typical application with a 5V power supply and an 8Ω
load, the maximum ambient temperature that allows maxi-
mum stereo power dissipation without exceeding the maxi-
mum junction temperature is approximately 48˚C.
TJMAX = PDMAX θJA + TA
(6)
Equation (6) gives the maximum junction temperature TJ
-
MAX. If the result violates the LM4816’s 150˚C, reduce the
maximum junction temperature by reducing the power sup-
ply voltage or increasing the load resistance. Further allow-
ance should be made for increased ambient temperatures.
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, single-
ended amplifiers require. Eliminating an output coupling ca-
pacitor in a single-ended configuration forces a single-supply
amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may perma-
nently damage loads such as speakers.
The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If twice the value given by Equation (3) exceeds the value
given by Equation (4), then decrease the supply voltage,
increase the load impedance, or reduce the ambient tem-
perature.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. 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
OUTPUT VOLTAGE LIMITER
The LM4816’s adjustable output voltage limiter can be used
to set a maximum and minimum output voltage swing mag-
nitude. The voltage applied to the VLIM input (pin 20) controls
the amount voltage limit magnitude.
Without the limiter’s influence (VLIM = 0V), the LM4816’s
maximum BTL output swing is nominally
2
PDMAX = (VDD
)
/ (2π2 RL) Single-Ended
(2)
2 x VDD
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
When the limiter input voltage is greater than 0V, the BTL
output voltage swing is
VOUT-BTL = (2 x VDD) - (4 x VLIM
)
The LM4816 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli-
fier. From Equation (3), assuming a 5V power supply and an
8Ω load, the maximum single channel power dissipation is
0.633W or 1.27W for stereo operation.
with a tolerance of 800 mV.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
2
PDMAX = 4 x (VDD
)
/ (2π2 RL) Bridge Mode
(3)
9
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power. Fortunately, many signal sources such as audio CO-
DECs have outputs of 1VRMS (2.83VP-P). Please refer to the
Audio Power Amplifier Design section for more informa-
tion on selecting the proper gain.
Application Information (Continued)
presence does not eliminate the need for a local 1.0µF
tantalum bypass capacitance connected between the
LM4816’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation in the output signal. Keep the length of leads and
traces that connect capacitors between the LM4816’s power
supply pin and ground as short as possible. Connecting a
1µF capacitor, CB, between the BYPASS pin and ground
improves the internal bias voltage’s stability and improves
the amplifier’s PSRR. The PSRR improvements increase as
the bypass pin capacitor value increases. Too large, how-
ever, increases turn-on time and can compromise amplifier’s
click and pop performance. The selection of bypass capaci-
tor values, especially CB, depends on desired PSRR require-
ments, click and pop performance (as explained in the sec-
tion, Proper Selection of External Components), system
cost, and size constraints.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (Ci in Figure 1). A high value capaci-
tor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap
little improvement by using large input capacitor.
Besides effecting system cost and size, Ci has an affect on
the LM4816’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 quies-
cent state. The magnitude of the pop is directly proportional
to the input capacitor’s size. Higher value capacitors need
more time to reach a quiescent DC voltage (usually VDD/2)
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
Rf. Thus, pops can be minimized by selecting an input
capacitor value that is no higher than necessary to meet the
desired -3dB frequency.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4816’s shutdown function. Activate micro-power shut-
down by applying VDD to the SHUTDOWN pin. When active,
the LM4816’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically VDD/2. The low 0.6µA typical
shutdown current is achieved by applying a voltage that is as
near as VDD as possible to the SHUTDOWN pin. A voltage
thrat is less than VDD may increase the shutdown current.
A 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 (7).
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 10kΩ pull-up resistor between the
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to VDD through the pull-up resistor, activat-
ing micro-power shutdown. The switch and resistor guaran-
tee 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.
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, CI, using Equation (4), is 0.063µF. The 1.0µF
CI shown in Figure 1 allows the LM4816 to drive high effi-
ciency, full range speaker whose response extends below
30Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of CB, the capacitor con-
nected to the BYPASS pin. Since CB determines how fast
the LM4816 settles to quiescent operation, its value is critical
when minimizing turn−on pops. The slower the LM4816’s
outputs ramp to their quiescent DC voltage (nominally 1/2
VDD), the smaller the turn−on pop. Choosing CB equal to
1.0µF along with a small value of Ci (in the range of 0.1µF to
0.39µF), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing Ci no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops.
TABLE 1. LOGIC LEVEL TRUTH TABLE FOR SHUT-
DOWN OPERATION
SHUTDOWN
OPERATIONAL MODE
Full power, stereo BTL
amplifiers
Low
High
Micro-power Shutdown
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4816’s performance requires properly se-
lecting external components. Though the LM4816 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4816 contains circuitry to minimize turn-on and shut-
down transients or "clicks and pop". For this discussion,
turn-on refers to either applying the power supply voltage or
when the shutdown mode is deactivated. While the power
supply is ramping to its final value, the LM4816’s internal
amplifiers are configured as unity gain buffers. An internal
current source changes the voltage of the BYPASS pin in a
controlled, linear manner. Ideally, the input and outputs track
The LM4816 is unity-gain stable, giving a 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 ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain demands input signals
with greater voltage swings to achieve maximum output
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10
VDD ≥ (VOUTPEAK + (VOD
+ VODBOT))
(9)
Application Information (Continued)
TOP
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches 1/2 VDD. As soon as the voltage on the
BYPASS pin is stable, the device becomes fully operational.
Although the bypass pin current cannot be modified, chang-
ing the size of CB alters the device’s turn-on time and the
magnitude of "clicks and pops". Increasing the value of CB
reduces the magnitude of turn-on pops. However, this pre-
sents a tradeoff: as the size of CB increases, the turn-on time
increases. There is a linear relationship between the size of
CB and the turn-on time. Here are some typical turn-on times
for various values of CB:
The Output Power vs Supply Voltage graph for an 8Ω load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4816 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation section.
After satisfying the LM4816’s power dissipation require-
ments, the minimum differential gain is found using Equation
(10).
CB
TON
20 ms
0.01µF
0.1µF
0.22µF
0.47µF
1.0µF
(10)
Thus, a minimum gain of 2.83 allows the LM4816’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let AVD = 3.
200 ms
440 ms
940 ms
2 Sec
The amplifier’s overall gain is set using the input (Ri) and
feedback (Rf) resistors. With the desired input impedance
set at 20kΩ, the feedback resistor is found using Equation
(11).
In order 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".
Rf/Ri = AVD/2
The value of Rf is 30kΩ.
(11)
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 re-
sponse 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 within the 0.25dB
desired limit. The results are an
NO LOAD STABILITY
The LM4816 may exhibit low level oscillation when the load
resistance is greater than 10kΩ. This oscillation only occurs
as the output signal swings near the supply voltages. Pre-
vent this oscillation by connecting a 5kΩ between the output
pins and ground.
AUDIO POWER AMPLIFIER DESIGN
fL = 100Hz/5 = 20Hz
(12)
(13)
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
and an
Power Output:
Load Impedance:
Input Level:
1WRMS
FH = 20kHzx5 = 100kHz
8Ω
1VRMS
As mentioned in the External Components section, Ri
and Ci create a highpass filter that sets the amplifier’s lower
bandpass frequency limit. Find the coupling capacitor’s
value using Equation (14).
Input Impedance:
Bandwidth:
20kΩ
100Hz−20 kHz 0.25 dB
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the Typical Performance Char-
acteristics section. Another way, using Equation (4), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac-
count for the amplifier’s dropout voltage, two additional volt-
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics curves, must be
added to the result obtained by Equation (8). The result in
Equation (9).
(14)
the result is
1/(2π*20kΩ*20Hz) = 0.398µF
(15)
Use a 0.39µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain, AVD, determines the
upper passband response limit. With AVD = 3 and fH
=
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4816’s 3.5MHz GBWP. With
(8)
11
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Application Information (Continued)
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance-restricting
bandwidth limitations.
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12
Physical Dimensions inches (millimeters) unless otherwise noted
20-Lead Molded PKG, TSSOP, JEDEC, 4.4mm BODY WIDTH
Order Number LM4816MT
NS Package Number MTC20
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whose failure to perform when properly used in
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2. A critical component is any component of a life
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can be reasonably expected to cause the failure of
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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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