LM4766
LM4766 Overture Audio Power Amplifier Series Dual 40W Audio Power
Amplifier with Mute
Literature Number: SNAS031E
LM4766 Overture™
Audio Power Amplifier Series Dual 40W Audio Power
Amplifier with Mute
General Description
The LM4766 is a stereo audio amplifier capable of delivering
typically 40W per channel with the non-isolated "T" package
and 30W per channel with the isolated "TF" package of
continuous average output power into an 8Ωload with less
than 0.1% (THD+N).
The performance of the LM4766, utilizing its Self Peak In-
stantaneous Temperature (˚Ke) (SPiKe™) Protection Cir-
cuitry, places it in a class above discrete and hybrid amplifi-
ers by providing an inherently, dynamically protected Safe
Operating Area (SOA). SPiKe Protection means that these
parts are safeguarded at the output against overvoltage,
undervoltage, overloads, including thermal runaway and in-
stantaneous temperature peaks.
Each amplifier within the LM4766 has an independent
smooth transition fade-in/out mute that minimizes output
pops. The IC’s extremely low noise floor at 2µV and its
extremely low THD+N value of 0.06% at the rated power
make the LM4766 optimum for high-end stereo TVs or mini-
component systems.
Key Specifications
jTHD+N at 1kHz at 2 x 30W continuous
average output power into 8Ω0.1% (max)
jTHD+N at 1kHz at continuous average
output power of 2 x 30W into 8Ω0.009% (typ)
Features
nSPiKe Protection
nMinimal amount of external components necessary
nQuiet fade-in/out mute mode
nNon-Isolated 15-lead TO-220 package
nWide Supply Range 20V - 78V
Applications
nHigh-end stereo TVs
nComponent stereo
nCompact stereo
Connection Diagram
Plastic Package
10092802
Top View
Non-Isolated TO-220 Package
Order Number LM4766T
See NS Package Number TA15A
Isolated TO-220 Package
Order Number LM4766TF
See NS Package Number TF15B
SPiKe™Protection and Overture™are trademarks of National Semiconductor Corporation.
March 2006
LM4766 Overture
™
Audio Power Amplifier Series
Dual 40W Audio Power Amplifier with Mute
© 2006 National Semiconductor Corporation DS100928 www.national.com
Typical Application
Note: Numbers in parentheses represent pinout for amplifier B.
*Optional component dependent upon specific design requirements.
10092801
FIGURE 1. Typical Audio Amplifier Application Circuit
LM4766
www.national.com 2
Absolute Maximum Ratings (Notes 4,
5)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage |V
CC
|+|V
EE
|
(No Input) 78V
Supply Voltage |V
CC
|+|V
EE
|
(with Input) 74V
Common Mode Input Voltage (V
CC
or V
EE
) and
|V
CC
|+|V
EE
|≤
60V
Differential Input Voltage 60V
Output Current Internally Limited
Power Dissipation (Note 6) 62.5W
ESD Susceptability (Note 7) 3000V
Junction Temperature (Note 8) 150˚C
Thermal Resistance
Non-Isolated T-Package
θ
JC
1˚C/W
Isolated TF-Package
θ
JC
2˚C/W
Soldering Information
T and TF Packages 260˚C
Storage Temperature −40˚C to +150˚C
Operating Ratings (Notes 4, 5)
Temperature Range
T
MIN
≤T
A
≤T
MAX
−20˚C ≤T
A
≤
+85˚C
Supply Voltage |V
CC
|+|V
EE
| (Note 1) 20V to 60V
Electrical Characteristics (Notes 4, 5)
The following specifications apply for V
CC
= +30V, V
EE
= −30V, I
MUTE
= −0.5mA with R
L
=8Ωunless otherwise specified. Lim-
its apply for T
A
= 25˚C.
Symbol Parameter Conditions LM4766 Units
(Limits)
Typical Limit
(Note 9) (Note 10)
|V
CC
| + Power Supply Voltage GND − V
EE
≥9V 18 20 V (min)
|V
EE
| (Note 11) 60 V (max)
P
O
Output Power T Package, V
CC
=±30V,
THD+N = 0.1% (max),
f = 1kHz, f = 20kHz
40 30 W/ch (min)
TF Package, V
CC
=±26V(Note 13),
THD+N = 0.1% (max),
30 25 W/ch (min)
(Notes 3, 13) (Continuous Average) f = 1kHz, f = 20kHz
THD+N Total Harmonic Distortion
Plus Noise
T Package
30W/ch, R
L
=8Ω, 20Hz ≤f≤20kHz,
A
V
= 26dB
0.06 %
TF Package
25W/ch, R
L
=8Ω, 20Hz ≤f≤20kHz,
A
V
= 26dB
0.06 %
X
talk
Channel Separation f = 1kHz, V
O
= 10.9Vrms 60 dB
SR
(Note 3)
Slew Rate V
IN
= 1.2Vrms, t
rise
= 2ns 9 5 V/µs (min)
I
total
Total Quiescent Power Both Amplifiers V
CM
= 0V, 48 100 mA (max)
(Note 2) Supply Current V
O
= 0V, I
O
= 0mA
V
OS
(Note 2)
Input Offset Voltage V
CM
= 0V, I
O
= 0mA 1 10 mV (max)
I
B
Input Bias Current V
CM
= 0V, I
O
= 0mA 0.2 1 µA (max)
I
OS
Input Offset Current V
CM
= 0V, I
O
= 0mA 0.01 0.2 µA (max)
I
O
Output Current Limit |V
CC
|=|V
EE
| = 10V, t
ON
= 10ms, 4 3 Apk (min)
V
O
=0V
V
OD
Output Dropout Voltage |V
CC
–V
O
|, V
CC
= 20V, I
O
= +100mA 1.5 4 V (max)
(Note 2) (Note 12) |V
O
–V
EE
|, V
EE
= −20V, I
O
= −100mA 2.5 4 V (max)
LM4766
www.national.com3
Electrical Characteristics (Notes 4, 5) (Continued)
The following specifications apply for V
CC
= +30V, V
EE
= −30V, I
MUTE
= −0.5mA with R
L
=8Ωunless otherwise specified. Lim-
its apply for T
A
= 25˚C.
Symbol Parameter Conditions LM4766 Units
(Limits)
Typical Limit
(Note 9) (Note 10)
PSRR Power Supply Rejection Ratio V
CC
= 30V to 10V, V
EE
= −30V, 125 85 dB (min)
(Note 2) V
CM
= 0V, I
O
= 0mA
V
CC
= 30V, V
EE
= −30V to −10V 110 85 dB (min)
V
CM
= 0V, I
O
= 0mA
CMRR Common Mode Rejection Ratio V
CC
= 50V to 10V, V
EE
= −10V to −50V, 110 75 dB (min)
(Note 2) V
CM
= 20V to −20V, I
O
= 0mA
A
VOL
(Note 2)
Open Loop Voltage Gain R
L
=2kΩ,∆V
O
= 40V 115 80 dB (min)
GBWP Gain Bandwidth Product f
O
= 100kHz, V
IN
= 50mVrms 8 2 MHz (min)
e
IN
Input Noise IHF–A Weighting Filter 2.0 8 µV (max)
(Note 3) R
IN
= 600Ω(Input Referred)
SNR Signal-to-Noise Ratio
P
O
= 1W, A–Weighted, 98 dB
Measured at 1kHz, R
S
=25Ω
P
O
= 25W, A–Weighted 112 dB
Measured at 1kHz, R
S
=25Ω
A
M
Mute Attenuation Pin 6,11 at 2.5V 115 80 dB (min)
Note 1: Operation is guaranteed up to 60V, however, distortion may be introduced from SPiKe Protection Circuitry if proper thermal considerations are not taken
into account. Refer to the Application Information section for a complete explanation.
Note 2: DC Electrical Test; Refer to Test Circuit #1.
Note 3: AC Electrical Test; Refer to Test Circuit #2.
Note 4: All voltages are measured with respect to the GND pins (5, 10), unless otherwise specified.
Note 5: 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 6: For operating at case temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance
of θJC = 1˚C/W (junction to case) for the T package. Refer to the section Determining the Correct Heat Sink in the Application Information section.
Note 7: Human body model, 100pF discharged through a 1.5kΩresistor.
Note 8: The operating junction temperature maximum is 150˚C, however, the instantaneous Safe Operating Area temperature is 250˚C.
Note 9: Typicals are measured at 25˚C and represent the parametric norm.
Note 10: Limits are guarantees that all parts are tested in production to meet the stated values.
Note 11: VEE must have at least −9V at its pin with reference to ground in order for the under-voltage protection circuitry to be disabled. In addition, the voltage
differential between VCC and VEE must be greater than 14V.
Note 12: The output dropout voltage, VOD, is the supply voltage minus the clipping voltage. Refer to the Clipping Voltage vs. Supply Voltage graph in the Typical
Performance Characteristics section.
Note 13: When using the isolated package (TF), the θJC is 2˚C/W verses 1˚C/W for the non-isolated package (T). This increased thermal resistance from junction
to case requires a lower supply voltage for decreased power dissipation within the package. Voltages higher than ±26V maybe used but will require a heat sink with
less than 1˚C/W thermal resistance to avoid activating thermal shutdown during normal operation.
LM4766
www.national.com 4
Bridged Amplifier Application Circuit
10092805
FIGURE 2. Bridged Amplifier Application Circuit
LM4766
www.national.com 6
Single Supply Application Circuit
Note: *Optional components dependent upon specific design requirements.
Auxiliary Amplifier Application Circuit
10092806
FIGURE 3. Single Supply Amplifier Application Circuit
10092807
FIGURE 4. Special Audio Amplifier Application Circuit
LM4766
www.national.com7
Equivalent Schematic
(excluding active protection circuitry)
LM4766 (One Channel Only)
10092808
LM4766
www.national.com 8
External Components Description
Components Functional Description
1R
B
Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load
upon power down of the system due to the low input impedance of the circuitry when the undervoltage
circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.
2R
i
Inverting input resistance to provide AC gain in conjunction with R
f
.
3R
f
Feedback resistance to provide AC gain in conjunction with R
i
.
4C
i
(Note 14)
Feedback capacitor which ensures unity gain at DC. Also creates a highpass filter with R
i
at f
C
= 1/(2πR
i
C
i
).
5C
S
Provides power supply filtering and bypassing. Refer to the Supply Bypassing application section for proper
placement and selection of bypass capacitors.
6R
V
(Note 14)
Acts as a volume control by setting the input voltage level.
7R
IN
(Note 14)
Sets the amplifier’s input terminals DC bias point when C
IN
is present in the circuit. Also works with C
IN
to
create a highpass filter at f
C
= 1/(2πR
IN
C
IN
). Refer to Figure 4.
8C
IN
(Note 14)
Input capacitor which blocks the input signal’s DC offsets from being passed onto the amplifier’s inputs.
9R
SN
(Note 14)
Works with C
SN
to stabilize the output stage by creating a pole that reduces high frequency instabilities.
10 C
SN
(Note 14)
Works with R
SN
to stabilize the output stage by creating a pole that reduces high frequency instabilities.
The pole is set at f
C
= 1/(2πR
SN
C
SN
). Refer to Figure 4.
11 L (Note 14) Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce
the Q of the series resonant circuit. Also provides a low impedance at low frequencies to short out R and
pass audio signals to the load. Refer to Figure 4.
12 R (Note 14)
13 R
A
Provides DC voltage biasing for the transistor Q1 in single supply operation.
14 C
A
Provides bias filtering for single supply operation.
15 R
INP
(Note 14)
Limits the voltage difference between the amplifier’s inputs for single supply operation. Refer to the Clicks
and Pops application section for a more detailed explanation of the function of R
INP
.
16 R
BI
Provides input bias current for single supply operation. Refer to the Clicks and Pops application section for
a more detailed explanation of the function of R
BI
.
17 R
E
Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the
half-supply point along with C
A
.
18 R
M
Mute resistance set up to allow 0.5mA to be drawn from pin 6 or 11 to turn the muting function off.
→R
M
is calculated using: R
M
≤(|V
EE
| − 2.6V)/l where l ≥0.5mA. Refer to the Mute Attenuation vs Mute
Current curves in the Typical Performance Characteristics section.
19 C
M
Mute capacitance set up to create a large time constant for turn-on and turn-off muting.
20 S
1
Mute switch that mutes the music going into the amplifier when opened.
Note 14: Optional components dependent upon specific design requirements.
LM4766
www.national.com9
Typical Performance Characteristics
THD+N vs Frequency THD+N vs Frequency
10092855 10092856
THD+N vs Output Power THD+N vs Output Power
10092858 10092857
THD+N vs Distribution THD+N vs Distribution
10092872 10092873
LM4766
www.national.com 10
Typical Performance Characteristics (Continued)
Channel Separation vs
Frequency
Clipping Voltage vs
Supply Voltage
10092810 10092868
Output Power vs
Load Resustance
Output Power vs
Supply Voltage
10092874 10092878
Power Dissipation vs
Output Power
Power Dissipation vs
Output Power
10092876 10092877
LM4766
www.national.com11
Typical Performance Characteristics (Continued)
Max Heatsink Thermal Resistance (˚C/W)
at the Specified Ambient Temperature (˚C)
10092875
Note: The maximum heatsink thermal resistance values,
θ
SA
, in the table above were calculated using a θ
CS
=
0.2˚C/W due to thermal compound.
Safe Area
SPiKe Protection
Response
10092859 10092860
Pulse Power Limit Pulse Power Limit
10092863 10092864
LM4766
www.national.com 12
Typical Performance Characteristics (Continued)
Pulse Response Large Signal Response
10092866
10092887
Power Supply
Rejection Ratio
Common-Mode
Rejection Ratio
10092888 10092889
Open Loop
Frequency Response
Supply Current vs
Case Temperature
10092890 10092865
LM4766
www.national.com13
Typical Performance Characteristics (Continued)
Input Bias Current vs
Case Temperature
Mute Attenuation vs
Mute Current (per Amplifier)
10092867 10092885
Mute Attenuation vs
Mute Current (per Amplifier)
Output Power/Channel
vs Supply Voltage
f = 1kHz, R
L
=4Ω, 80kHz BW
10092886
10092891
Output Power/Channel
vs Supply Voltage
f = 1kHz, R
L
=6Ω, 80kHz BW
Output Power/Channel
vs Supply Voltage
f = 1kHz, R
L
=8Ω, 80kHz BW
10092892 10092893
LM4766
www.national.com 14
Application Information
MUTE MODE
The muting function of the LM4766 allows the user to mute
the music going into the amplifier by drawing more than
0.5mA out of each mute pin on the device. This is accom-
plished as shown in the Typical Application Circuit where the
resistor R
M
is chosen with reference to your negative supply
voltage and is used in conjunction with a switch. The switch
when opened cuts off the current flow from pin 6 or 11 to
−V
EE
, thus placing the LM4766 into mute mode. Refer to the
Mute Attenuation vs Mute Current curves in the Typical
Performance Characteristics section for values of attenu-
ation per current out of pins 6 or 11. The resistance R
M
is
calculated by the following equation:
R
M
≤(|−V
EE
| − 2.6V)/I
pin6
where I
pin6
=I
pin11
≥0.5mA.
Both pins 6 and 11 can be tied together so that only one
resistor and capacitor are required for the mute function. The
mute resistance must be chosen such that greater than 1mA
is pulled through the resistor R
M
so that each amplifier is fully
pulled out of mute mode. Taking into account supply line
fluctuations, it is a good idea to pull out 1mA per mute pin or
2 mA total if both pins are tied together.
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection cir-
cuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning
on the LM4766 such that no DC output spikes occur. Upon
turn-off, the output of the LM4766 is brought to ground
before the power supplies such that no transients occur at
power-down.
OVER-VOLTAGE PROTECTION
The LM4766 contains over-voltage protection circuitry that
limits the output current to approximately 4.0A
PK
while also
providing voltage clamping, though not through internal
clamping diodes. The clamping effect is quite the same,
however, the output transistors are designed to work alter-
nately by sinking large current spikes.
SPiKe PROTECTION
The LM4766 is protected from instantaneous peak-
temperature stressing of the power transistor array. The Safe
Operating graph in the Typical Performance Characteris-
tics section shows the area of device operation where
SPiKe Protection Circuitry is not enabled. The waveform to
the right of the SOA graph exemplifies how the dynamic
protection will cause waveform distortion when enabled.
Please refer to AN-898 for more detailed information.
THERMAL PROTECTION
The LM4766 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die reaches 165˚C, the LM4766 shuts
down. It starts operating again when the die temperature
drops to about 155˚C, but if the temperature again begins to
rise, shutdown will occur again at 165˚C. Therefore, the
device is allowed to heat up to a relatively high temperature
if the fault condition is temporary, but a sustained fault will
cause the device to cycle in a Schmitt Trigger fashion be-
tween the thermal shutdown temperature limits of 165˚C and
155˚C. This greatly reduces the stress imposed on the IC by
thermal cycling, which in turn improves its reliability under
sustained fault conditions.
Since the die temperature is directly dependent upon the
heat sink used, the heat sink should be chosen such that
thermal shutdown will not be reached during normal opera-
tion. Using the best heat sink possible within the cost and
space constraints of the system will improve the long-term
reliability of any power semiconductor device, as discussed
in the Determining the Correct Heat Sink Section.
DETERMlNlNG MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understand-
ing if optimum power output is to be obtained. An incorrect
maximum power dissipation calculation may result in inad-
equate heat sinking causing thermal shutdown and thus
limiting the output power.
Equation (1) exemplifies the theoretical maximum power
dissipation point of each amplifier where V
CC
is the total
supply voltage.
P
DMAX
=V
CC2
/2π
2
R
L
(1)
Thus by knowing the total supply voltage and rated output
load, the maximum power dissipation point can be calcu-
lated. The package dissipation is twice the number which
results from Equation (1) since there are two amplifiers in
each LM4766. Refer to the graphs of Power Dissipation
versus Output Power in the Typical Performance Charac-
teristics section which show the actual full range of power
dissipation not just the maximum theoretical point that re-
sults from Equation (1).
DETERMINING THE CORRECT HEAT SINK
The choice of a heat sink for a high-power audio amplifier is
made entirely to keep the die temperature at a level such
that the thermal protection circuitry does not operate under
normal circumstances.
The thermal resistance from the die (junction) to the outside
air (ambient) is a combination of three thermal resistances,
θ
JC
,θ
CS
, and θ
SA
. In addition, the thermal resistance, θ
JC
(junction to case), of the LM4766T is 1˚C/W. Using Thermal-
loy Thermacote thermal compound, the thermal resistance,
θ
CS
(case to sink), is about 0.2˚C/W. Since convection heat
flow (power dissipation) is analogous to current flow, thermal
resistance is analogous to electrical resistance, and tem-
perature drops are analogous to voltage drops, the power
dissipation out of the LM4766 is equal to the following:
P
DMAX
=(T
JMAX
−T
AMB
)/θ
JA
(2)
where T
JMAX
= 150˚C, T
AMB
is the system ambient tempera-
ture and θ
JA
=θ
JC
+θ
CS
+θ
SA
.
10092852
Once the maximum package power dissipation has been
calculated using Equation (1), the maximum thermal resis-
tance, θ
SA
, (heat sink to ambient) in ˚C/W for a heat sink can
be calculated. This calculation is made using Equation (3)
which is derived by solving for θ
SA
in Equation (2).
θ
SA
= [(T
JMAX
−T
AMB
)−P
DMAX
(θ
JC
+θ
CS
)]/P
DMAX
(3)
LM4766
www.national.com15
Application Information (Continued)
Again it must be noted that the value of θ
SA
is dependent
upon the system designer’s amplifier requirements. If the
ambient temperature that the audio amplifier is to be working
under is higher than 25˚C, then the thermal resistance for the
heat sink, given all other things are equal, will need to be
smaller.
SUPPLY BYPASSING
The LM4766 has excellent power supply rejection and does
not require a regulated supply. However, to improve system
performance as well as eliminate possible oscillations, the
LM4766 should have its supply leads bypassed with low-
inductance capacitors having short leads that are located
close to the package terminals. Inadequate power supply
bypassing will manifest itself by a low frequency oscillation
known as “motorboating” or by high frequency instabilities.
These instabilities can be eliminated through multiple by-
passing utilizing a large tantalum or electrolytic capacitor
(10µF or larger) which is used to absorb low frequency
variations and a small ceramic capacitor (0.1µF) to prevent
any high frequency feedback through the power supply lines.
If adequate bypassing is not provided, the current in the
supply leads which is a rectified component of the load
current may be fed back into internal circuitry. This signal
causes distortion at high frequencies requiring that the sup-
plies be bypassed at the package terminals with an electro-
lytic capacitor of 470µF or more.
BRIDGED AMPLIFIER APPLICATION
The LM4766 has two operational amplifiers internally, allow-
ing for a few different amplifier configurations. One of these
configurations is referred to as “bridged mode” and involves
driving the load differentially through the LM4766’s outputs.
This configuration is shown in Figure 2. Bridged mode op-
eration is different from the classical single-ended amplifier
configuration where one side of its load is connected to
ground.
A bridge amplifier design has a distinct advantage over the
single-ended configuration, as it provides differential drive to
the load, thus doubling output swing for a specified supply
voltage. Consequently, theoretically four times the output
power is possible as compared to a single-ended amplifier
under the same conditions. This increase in attainable output
power assumes that the amplifier is not current limited or
clipped.
A direct consequence of the increased power delivered to
the load by a bridge amplifier is an increase in internal power
dissipation. For each operational amplifier in a bridge con-
figuration, the internal power dissipation will increase by a
factor of two over the single ended dissipation. Thus, for an
audio power amplifier such as the LM4766, which has two
operational amplifiers in one package, the package dissipa-
tion will increase by a factor of four. To calculate the
LM4766’s maximum power dissipation point for a bridged
load, multiply Equation (1) by a factor of four.
This value of P
DMAX
can be used to calculate the correct size
heat sink for a bridged amplifier application. Since the inter-
nal dissipation for a given power supply and load is in-
creased by using bridged-mode, the heatsink’s θ
SA
will have
to decrease accordingly as shown by Equation (3). Refer to
the section, Determining the Correct Heat Sink, for a more
detailed discussion of proper heat sinking for a given appli-
cation.
SINGLE-SUPPLY AMPLIFIER APPLICATION
The typical application of the LM4766 is a split supply am-
plifier. But as shown in Figure 3, the LM4766 can also be
used in a single power supply configuration. This involves
using some external components to create a half-supply bias
which is used as the reference for the inputs and outputs.
Thus, the signal will swing around half-supply much like it
swings around ground in a split-supply application. Along
with proper circuit biasing, a few other considerations must
be accounted for to take advantage of all of the LM4766
functions, like the mute function.
CLICKS AND POPS
In the typical application of the LM4766 as a split-supply
audio power amplifier, the IC exhibits excellent “click” and
“pop” performance when utilizing the mute mode. In addition,
the device employs Under-Voltage Protection, which elimi-
nates unwanted power-up and power-down transients. The
basis for these functions are a stable and constant half-
supply potential. In a split-supply application, ground is the
stable half-supply potential. But in a single-supply applica-
tion, the half-supply needs to charge up just like the supply
rail, V
CC
. This makes the task of attaining a clickless and
popless turn-on more challenging. Any uneven charging of
the amplifier inputs will result in output clicks and pops due to
the differential input topology of the LM4766.
To achieve a transient free power-up and power-down, the
voltage seen at the input terminals should be ideally the
same. Such a signal will be common-mode in nature, and
will be rejected by the LM4766. In Figure 3, the resistor R
INP
serves to keep the inputs at the same potential by limiting the
voltage difference possible between the two nodes. This
should significantly reduce any type of turn-on pop, due to an
uneven charging of the amplifier inputs. This charging is
based on a specific application loading and thus, the system
designer may need to adjust these values for optimal perfor-
mance.
As shown in Figure 3, the resistors labeled R
BI
help bias up
the LM4766 off the half-supply node at the emitter of the
2N3904. But due to the input and output coupling capacitors
in the circuit, along with the negative feedback, there are two
different values of R
BI
, namely 10kΩand 200kΩ. These
resistors bring up the inputs at the same rate resulting in a
popless turn-on. Adjusting these resistors values slightly
may reduce pops resulting from power supplies that ramp
extremely quick or exhibit overshoot during system turn-on.
LM4766
www.national.com 16
Application Information (Continued)
AUDIO POWER AMPLlFIER DESIGN
Design a 30W/8ΩAudio Amplifier
Given:
Power Output 30Wrms
Load Impedance 8Ω
Input Level 1Vrms(max)
Input Impedance 47kΩ
Bandwidth 20Hz−20kHz
±0.25dB
A designer must first determine the power supply require-
ments in terms of both voltage and current needed to obtain
the specified output power. V
OPEAK
can be determined from
Equation (4) and I
OPEAK
from Equation (5).
(4)
(5)
To determine the maximum supply voltage the following
conditions must be considered. Add the dropout voltage to
the peak output swing V
OPEAK
, to get the supply rail at a
current of I
OPEAK
. The regulation of the supply determines
the unloaded voltage which is usually about 15% higher. The
supply voltage will also rise 10% during high line conditions.
Therefore the maximum supply voltage is obtained from the
following equation.
Max supplies ≈±(V
OPEAK
+V
OD
) (1 + regulation) (1.1)
For 30W of output power into an 8Ωload, the required
V
OPEAK
is 21.91V. A minimum supply rail of 25.4V results
from adding V
OPEAK
and V
OD
. With regulation, the maximum
supplies are ±32V and the required I
OPEAK
is 2.74A from
Equation (5). It should be noted that for a dual 30W amplifier
into an 8Ωload the I
OPEAK
drawn from the supplies is twice
2.74A
PK
or 5.48A
PK
. At this point it is a good idea to check
the Power Output vs Supply Voltage to ensure that the
required output power is obtainable from the device while
maintaining low THD+N. In addition, the designer should
verify that with the required power supply voltage and load
impedance, that the required heatsink value θ
SA
is feasible
given system cost and size constraints. Once the heatsink
issues have been addressed, the required gain can be de-
termined from Equation (6).
(6)
From Equation (6), the minimum A
V
is: A
V
≥15.5.
By selecting a gain of 21, and with a feedback resistor, R
f
=
20kΩ, the value of R
i
follows from Equation (7).
R
i
=R
f
(A
V
− 1) (7)
Thus with R
i
=1kΩa non-inverting gain of 21 will result.
Since the desired input impedance was 47kΩ, a value of
47kΩwas selected for R
IN
. The final design step is to
address the bandwidth requirements which must be stated
as a pair of −3dB frequency points. Five times away from a
−3dB point is 0.17dB down from passband response which
is better than the required ±0.25dB specified. This fact re-
sults in a low and high frequency pole of 4Hz and 100kHz
respectively. As stated in the External Components sec-
tion, R
i
in conjunction with C
i
create a high-pass filter.
C
i
≥1/(2π*1kΩ* 4Hz) = 39.8µF; use 39µF.
The high frequency pole is determined by the product of the
desired high frequency pole, f
H
, and the gain, A
V
. With a
A
V
= 21 and f
H
= 100kHz, the resulting GBWP is 2.1MHz,
which is less than the guaranteed minimum GBWP of the
LM4766 of 8MHz. This will ensure that the high frequency
response of the amplifier will be no worse than 0.17dB down
at 20kHz which is well within the bandwidth requirements of
the design.
LM4766
www.national.com17
Physical Dimensions inches (millimeters)
unless otherwise noted
Non-Isolated TO-220 15-Lead Package
Order Number LM4766T
NS Package Number TA15A
LM4766
www.national.com 18
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Isolated TO-220 15-Lead Package
Order Number LM4766TF
NS Package Number TF15B
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.
For the most current product information visit us at www.national.com.
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.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
Leadfree products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: ap.support@nsc.com
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
LM4766 Overture
™
Audio Power Amplifier Series
Dual 40W Audio Power Amplifier with Mute
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,
and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should
obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are
sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard
warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where
mandated by government requirements, testing of all parameters of each product is not necessarily performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,
or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a
warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual
property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied
by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive
business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional
restrictions.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all
express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not
responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably
be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing
such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be
provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in
such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic."Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at
the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are
designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated
products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:
Products Applications
Audio www.ti.com/audio Communications and Telecom www.ti.com/communications
Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers
Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps
DLP®Products www.dlp.com Energy and Lighting www.ti.com/energy
DSP dsp.ti.com Industrial www.ti.com/industrial
Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical
Interface interface.ti.com Security www.ti.com/security
Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense
Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive
Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video
RFID www.ti-rfid.com
OMAP Mobile Processors www.ti.com/omap
Wireless Connectivity www.ti.com/wirelessconnectivity
TI E2E Community Home Page e2e.ti.com
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright ©2011, Texas Instruments Incorporated
