LM4876MX/NOPB [NSC]
IC 1.5 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8, SOIC-8, Audio/Video Amplifier;
| 型号： | LM4876MX/NOPB |
| 厂家： | 
National Semiconductor |
| 描述： | IC 1.5 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8, SOIC-8, Audio/Video Amplifier 放大器 光电二极管 商用集成电路 |
| 文件： | 总12页 (文件大小：312K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
March 2003
LM4876
1.1W Audio Power Amplifier with Logic Low Shutdown
General Description
Key Specifications
The LM4876 is a single 5V supply bridge-connected audio
power amplifier capable of delivering 1.1W (typ) of continu-
ous average power to an 8Ω load with 0.5% THD+N.
j
THD+N at 1kHz for 1W continuous
average output power into 8Ω
Output power at 1kHz into 8Ω
with 10% THD+N
0.5% (max)
1.5W (typ)
j
Like other audio amplifiers in the Boomer series, the LM4876
is designed specifically to provide high quality output power
with a minimal amount of external components. The LM4876
does not require output coupling capacitors, bootstrap ca-
pacitors, or snubber networks. It is perfectly suited for low-
power portable systems.
j
j
Shutdown current
0.01µA (typ)
2.0V to 5.5V
Supply voltage range
Features
The LM4876 features an active low externally controlled,
micro-power shutdown mode. Additionally, the LM4876 fea-
tures an internal thermal shutdown protection mechanism.
For PCB space efficiency, the LM4876 is available in MSOP
and SO surface mount packages.
n Does not require output coupling capacitors, bootstrap
capacitors, or snubber circuits
n 10-pin MSOP and 8-pin SO packages
n Unity-gain stable
n External gain set
The unity-gain stable LM4876’s closed loop gain is set using
external resistors.
Applications
n Mobile Phones
n Portable Computers
n Desktop Computers
n Low-Voltage Audio Systems
Typical Application
10129901
FIGURE 1. Typical LM4876 Audio Amplifier Application Circuit.
Numbers in ( ) are specific to the 10-pin MSOP package
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation
DS101299
www.national.com
Connection Diagrams
Mini Small Outline MSOP Package
10129925
Top View
Order Number LM4876MM
See NS Package Number MUB10A
Small Outline SO Package
10129902
Top View
Order Number LM4876M
See NS Package Number M08A
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2
Absolute Maximum Ratings (Note 2)
Infrared (15 sec.)
220˚C
See AN-450 "Surface Mounting and their Effects on
Product Reliability" for other methods of
soldering surface mount devices.
θJC (typ)—MUB10A
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
6.0V
−65˚C to +150˚C
−0.3V to VDD +0.3V
Internally Limited
2500V
56˚C/W
Storage Temperature
Input Voltage
θJA (typ)—MUB10A
θJC (typ)—M08A
θJA (typ)—M08A
210˚C/W
35˚C/W
Power Dissipation (Note 3)
ESD Susceptibility (Note 4)
ESD Susceptibility (Note 5)
Junction Temperature
Soldering Information
Small Outline Package
Vapor Phase (60 sec.)
140˚C/W
250V
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage
150˚C
−40˚C ≤ TA ≤ 85˚C
2.0V ≤ VDD ≤ 5.5V
215˚C
Electrical Characteristics (Notes 1, 2)
The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25˚C.
LM4876
Units
(Limits)
Symbol
VDD
Parameter
Supply Voltage
Conditions
Typical
Limit
(Note 6)
(Note 7)
2.0
V (min)
V (max)
5.5
IDD
ISD
VOS
Po
Quiescent Power Supply Current
Shutdown Current
VIN = 0V, Io = 0A
6.5
0.01
5
10.0
2
mA (max)
µA (max)
mV (max)
W (min)
VPIN1 = 0V
Output Offset Voltage
Output Power
VIN = 0V
50
THD = 0.5% (max); f = 1 kHz;
RL = 8Ω
1.10
1.0
THD+N = 10%; f = 1 kHz;
RL = 8Ω
1.5
0.25
65
W
%
THD+N
PSRR
Total Harmonic Distortion+Noise
Power Supply Rejection Ratio
Po = 1 Wrms; AVD = 2; 20 Hz ≤ f ≤
20 kHz; RL = 8Ω
VDD = 4.9V to 5.1V
dB
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified.
Note 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 guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions that
guarantee specific performance limits. This assumes that the device operates within the Operating Ratings. Specifications are not guaranteed for parameters where
no limit is given. The typical value, however, is a good indication of device performance.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
, θ , and the ambient temperature T . The maximum
A
JMAX JA
allowable power dissipation is P
= (T
–T )/θ or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4876, T = 150˚C.
DMAX
JMAX
A
JA
JMAX
The typical junction-to-ambient thermal resistance is 140˚C/W for the M08A package and 210˚C/W for the MUB10A package.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Machine Model, 220 pF–240 pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Electrical Characteristics VDD = 5/3.3/2.6V
LM4876
Typical
(Note 6)
Units
(Limits)
Symbol
Parameter
Conditions
Limit
(Note 7)
1.2
VIH
VIL
Shutdown Input Voltage High
Shutdown Input Voltage Low
V(min)
V(max)
0.4
3
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External Components Description
(Figure 1)
Components
Functional Description
1.
Ri
Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a
high pass filter with Ci at fC= 1/(2π RiCi).
2.
Ci
Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a
highpass filter with Ri at fC = 1/(2π RiCi). Refer to the section, Proper Selection of External Components,
for an explanation of how to determine the value of Ci.
3.
4.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
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.
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.
5.
CB
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Frequency
10129903
10129904
THD+N vs Frequency
THD+N vs Output Power
10129905
10129906
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4
Typical Performance Characteristics (Continued)
THD+N vs Output Power
THD+N vs Output Power
10129907
10129908
10129910
10129911
Output Power vs
Supply Voltage
Output Power vs
Supply Voltage
10129909
Output Power vs
Supply Voltage
Output Power vs
Supply Voltage
10129911
5
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Typical Performance Characteristics (Continued)
Output Power vs
Load Resistance
Power Dissipation vs
Output Power
10129912
10129913
Clipping Voltage vs
Supply Voltage
Power Derating Curve
10129915
10129914
Frequency Response vs
Input Capacitor Size
Noise Floor
10129916
10129917
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6
Typical Performance Characteristics (Continued)
Power Supply
Rejection Ratio
Open Loop
Frequency Response
10129918
10129919
Supply Current vs
Shutdown Voltage
Supply Current vs
Supply Voltage
@
LM4876 VDD = 5/3.3/2.6Vdc
10129920
10129923
7
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dissipation supported by the IC packaging. Rearranging
Equation (4) results in Equation (5). This equation gives the
maximum ambient temperature that still allows maximum
power dissipation without violating the LM4876’s maximum
junction temperature.
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4876 consists of two opera-
tional amplifiers. External resistors Rf and Ri set the closed-
loop gain of Amp1, whereas two internal 40kΩ resistors set
Amp2’s gain at -1. The LM4876 drives a load, such as a
speaker, connected between the two amplifier outputs, Vo1
and Vo2 .
TA = TJMAX - PDMAX θJA
(5)
For a typical application with a 5V power supply and an 8W
load, the maximum ambient temperature that allows maxi-
mum power dissipation without exceeding the maximum
junction temperature is approximately 61˚C.
Figure 1 shows that the Amp1 output serves as the Amp2
input, which 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 Vo1 and
Vo2 and driven differentially (commonly referred to as
"bridge mode"). This results in a differential gain of
TJMAX = PDMAX θJA + TA
(6)
For the MSOP10A package, θJA = 210˚C/W. Equation (6)
shows that TJMAX , for the MSOP10 package, is 158˚C for an
ambient temperature of 25˚C and using the same 5V power
supply and an 8Ω load. This violates the LM4876’s 150˚C
maximum junction temperature when using the MSOP10A
package. Reduce the junction temperature by reducing the
power supply voltage or increasing the load resistance. Fur-
ther, allowance should be made for increased ambient tem-
peratures. To achieve the same 61˚C maximum ambient
temperature found for the MO8 package, the MSOP10 pack-
aged part should operate on a 4.1V supply voltage when
driving an 8Ω load. Alternatively, a 5V supply can be used
when driving a load with a minimum resistance of 12Ω for the
same 61˚C maximum ambient temperature.
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 power assumes that the ampli-
fier is not current limited or that 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 section.
Fully charged Li-ion batteries typically supply 4.3V to por-
table applications such as cell phones. This supply voltage
allows the LM4876 to drive loads with a minimum resistance
of 9Ω without violating the maximum junction temperature
when the maximum ambient temperature is 61˚C.
Another advantage of the differential bridge output is no net
DC voltage across the load. This results from biasing Vo1
and Vo2 at half-supply. This eliminates the coupling capaci-
tor that single supply, single-ended amplifiers require. Elimi-
nating an output coupling capacitor in a single-ended con-
figuration 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 dissipa-
tion and may permanently 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 the result of Equation (3) is greater than that of Equation
(4), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce θJA. The heat sink can be created using additional
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. When
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 output load.
adding a heat sink, the θJA is the sum of θJC, θCS, and θSA
.
( θJC is the junction-to-case thermal impedance, θCS is the
case-to-sink thermal impedance, and θSA is the sink-to-
ambient thermal impedance.) Refer to the Typical Perfor-
mance Characteristics curves for power dissipation infor-
mation at lower output power levels.
2
PDMAX = (VDD
)
/(2π2 RL) Single-Ended
(2)
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.
The LM4876 has two operational amplifiers in one package
and the maximum internal power dissipation is four times
that of a single-ended amplifier. Equation (3) states the
maximum power dissipation for a bridge amplifier. However,
even with this substantial increase in power dissipation, the
LM4876 does not require heatsinking. From Equation (3),
assuming a 5V power supply and an 8Ω load, the maximum
power dissipation point is 633mW.
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
presence does not eliminate the need for local bypass ca-
pacitance at the LM4876’s supply pins. Keep the length of
leads and traces that connect capacitors between the
LM4876’s power supply pin and ground as short as possible.
Connecting a 1µF capacitor 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, however, and the amplifier’s click and pop perfor-
2
PDMAX = 4*(VDD
)
/(2π2 RL ) Bridge Mode
(3)
The maximum power dissipation point given by Equation (3)
must not exceed the power dissipation given by Equation
(4):
PDMAX = (TJMAX -TA) /θJA
(4)
The LM4876’s TJMAX = 150˚C. In the M08A package, the
LM4876’s θJA is 140˚C/W. At any given ambient temperature
TA, use Equation (4) to find the maximum internal power
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8
with greater voltage swings to achieve maximum output
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)
mance can be compromised. The selection of bypass ca-
pacitor values, especially CB, depends on desired PSRR
requirements, click and pop performance (as explained in
the section, 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 150 Hz. Applications
using speakers with this limited low frequency response reap
little improvement by using a large input capacitor.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4876’s shutdown function. Activate micro-power shut-
down by applying a voltage below 400mV to the SHUT-
DOWN pin. When active, the LM4876’s micro-power shut-
down feature turns off the amplifier’s bias circuitry, reducing
the supply current. Though the LM4876 is in shutdown when
400mV is applied to the SHUTDOWN pin, the supply current
may be higher than 0.01µA (typ) shutdown current. There-
fore, for the lowest supply current during shutdown, connect
the SHUTDOWN pin to ground. The relationship between
the supply voltage, the shutdown current, and the voltage
applied to the SHUTDOWN pin is shown in Typical Perfor-
mance Characteristics curves.
Besides affecting system cost and size, Ci also affects the
LM4876’s click and pop performance. When the supply volt-
age 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 size. Higher value capacitors need more
time to reach a quiescent DC voltage (usually VCC/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.
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 pull-down resistor between the SHUT-
DOWN pin and GND. Connect the switch between the
SHUTDOWN pin and VCC. Select normal amplifier operation
by closing the switch. Opening the switch connects the
SHUTDOWN pin to GND through the pull-down resistor,
activating micro-power shutdown. The switch and resistor
guarantee that the SHUTDOWN pin will not float. This pre-
vents unwanted state changes. In a system with a micropro-
cessor or a microcontroller, use a digital output to apply the
control voltage to the SHUTDOWN pin. Driving the SHUT-
DOWN pin with active circuitry eliminates the pull down
resistor.
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 (7).
f-3dB = 2πRINCI
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, Equation (7) gives a value of Ci equal to
0.1µF. The 0.22µF Ci shown in Figure 1 allows for a speaker
whose response extends down to 75Hz.
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 LM4876 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4876’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 as small as possible
helps minimize clicks and pops.
SELECTING POWER EXTERNAL COMPONENTS
Optimizing the LM4876’s performance requires properly se-
lecting external components. Though the LM4876 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4876 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
9
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Application Information (Continued)
AUDIO POWER AMPLIFIER DESIGN
(10)
Thus, a minimum gain of 2.83 allows the LM4876’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let AVD = 3.
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
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).
Power Output
Load Impedance
Input Level
1WRMS
8Ω
1VRMS
Input Impedance
Bandwidth
20kΩ
Rf/Ri = AVD/2
(11)
100Hz–20kHz 0.25dB
The value of Rf is 30kΩ.
The last step in this design example is setting the amplifier’s
-3dB low frequency bandwidth. To achieve the desired
0.25dB pass band magnitude variation limit, the low fre-
quency response must extend to at least one-fifth the lower
bandwidth limit and the high frequency response must ex-
tend to at least five times the upper bandwidth limit. The
results is an
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 (8), 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). This results in
Equation (9).
fL = 100 Hz/5 = 20Hz
and an
FH = 20 kHz*5 = 100kHz
As mentioned in the External Components section, Ri and Ci
create a highpass filter that sets the amplifier’s lower band-
pass frequency limit. Find the coupling capacitor’s value
using Equation (12).
(8)
Ci ≥ 1/(2πRifL)
(12)
VCC ≥ (VOUTPEAK + (VOD
+ VODBOT))
(9)
TOP
The result is
1/(2π*20kΩ*20Hz) = 0.398µF.
Use a 0.39µF capacitor, the closest standard value.
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
LM4876 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 violation of maximum
power dissipation as explained above in the Power Dissi-
pation section.
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
150kHz. This is less than the LM4876’s 4MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain and avoid performance-restricting
bandwidth limitations.
After satisfying the LM4876’s power dissipation require-
ments, the minimum differential gain is found using Equation
(10).
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10
Physical Dimensions inches (millimeters)
unless otherwise noted
Order Number LM4876MM
NS Package Number MUB10A
Order Number LM4876M
NS Package Number M08A
11
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Notes
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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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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