NSC LM4731TA Stereo 25w audio power amplifier with mute and standby mode Datasheet

LM4731
Stereo 25W Audio Power Amplifier with Mute and
Standby Modes
General Description
Key Specifications
The LM4731 is a stereo audio amplifier capable of delivering
typically 25W per channel of continuous average output
power into a 4Ω or 8Ω load with less than 10% THD+N from
20Hz - 20kHz.
Each amplifier has an independent smooth transition fadein/out mute and a power conserving standby mode which
can be controlled by external logic.
The LM4731 has short circuit protection and a thermal shut
down feature that is activated when the die temperature
exceeds 150˚C. The LM4731 also has a under voltage lock
out feature for click and pop free power off and on.
The LM4731 has a wide operating supply range from +/-10V
- +/-28V allowing for lower cost unregulated power supplies
to be used.
j Output Power into 4Ω or 8Ω, 10% THD+N
j THD+N at 1kHz with 2 x 1W into 8Ω
j Mute Attenuation
25W (typ)
0.02% (typ)
85dB (typ)
j PSRR with fRIPPLE = 120Hz,
VRIPPLE = 1VRMS
50dB (typ)
j Slew Rate
18V/µs (typ)
j Standby Current (+/-22V)
4.8mA (typ)
Features
n Minimal amount of external components necessary
n Quiet fade-in/out mute mode
n Low current Standby-mode
Applications
n
n
n
n
n
Audio
Audio
Audio
Audio
Audio
amplifier
amplifier
amplifier
amplifier
amplifier
for
for
for
for
for
high-end stereo TVs
component stereo
compact stereo
PC satellite speaker systems
self powered speakers
Connection Diagrams
Plastic Package
TO-220 Top Marking (Note 12)
20060375
20060352
Top View
Non-Isolated Package
Order Number LM4731TA
See NS Package Number TA15A
© 2003 National Semiconductor Corporation
DS200603
Top View
U - Wafer Fab Code
Z - Assembly Plant Code
XY - Date Code
TT - Die Traceability
LM4731TA - LM4731TA
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LM4731 Stereo 25W Audio Power Amplifier with Mute and Standby Modes
July 2003
LM4731
Typical Application
20060353
FIGURE 1. Typical Audio Amplifier Application Circuit
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2
Soldering Information
(Notes 1,
T Package (10 sec.)
2)
+
-
Supply Voltage |V | + |V |
Common Mode Input Voltage
Differential Input Voltage
Output Current
−40˚C to +150˚C
Thermal Resistance
56V
θJA (TA)
43˚C/W
θJC (TA)
1.5˚C/W
V+ or V-
Operating Ratings (Notes 1, 2)
56V
Internally Limited
Power Dissipation (Note 3)
50W
ESD Susceptability (Note 4)
2.0kV
ESD Susceptability (Note 6)
250V
Junction Temperature (TJMAX) (Note 9)
260˚C
Storage Temperature
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Temperature Range
TMIN ≤ TA ≤ TMAX
−20˚C ≤ TA ≤ +85˚C
20V ≤ VTOTAL ≤ 56V
Supply Voltage |V+| + |V-|
150˚C
Electrical Characteristics (Notes 1, 2)
The following specifications apply for V+ = +22V, V- = −22V and RL = 8Ω unless otherwise specified. Limits apply for TA =
25˚C.
Symbol
Parameter
Conditions
|V+| + |V-|
Power Supply Voltage (Note 10) GND − V- ≥ 9V
AM
Mute Attenuation
PO
Output Power (RMS)
LM4731
Typical
Limit
(Note 6)
(Notes 7, 8)
20
56
85
Units
(Limits)
V (min)
V (max)
dB
THD+N = 10% (max), f = 1kHz
|V+| = |V-| = 18V, RL = 4Ω
|V+| = |V-| = 22V, RL = 8Ω
25
25
20
22
W (min)
W (min)
THD+N = 1% (max), f = 1kHz
|V+| = |V-| =18V, RL = 4Ω
|V+| = |V-| = 22V, RL = 8Ω
20
20
18
18
W (min)
W (min)
0.03
0.02
0.5
0.3
% (max)
% (max)
THD+N
Total Harmonic Distortion +
Noise
PO = 1W, f = 1kHz
AV = 26dB,
|V+| = |V-| = 18V, RL = 4Ω
|V+| = |V-| = 22V, RL = 8Ω
Xtalk
Channel Separation
PO = 10W
f = 1kHz
f = 10kHz
65
60
dB
dB
SR
Slew Rate (Note 11)
VIN = 2.0Vp-p, trise = 2ns
18
V/µs
IDD
Total Quiescent Power Supply
Current
VCM = 0V, VO = 0V, IO = 0A
Standby off (Play Mode)
Standby on (Standby Mode)
95
4.8
110
6
mA (max)
mA (max)
15
mV (max)
VOS
Input Offset Voltage
VCM = 0V, IO = 0 mA
2.0
IB
Input Bias Current
VCM = 0V, IO = 0 mA
0.2
µA
PSRR
Power Supply Rejection Ratio
VRIPPLE = 1VRMS, fRIPPLE = 120Hz sine
wave
Inputs terminated to GND
50
dB
AVOL
Open Loop Voltage Gain
RL = 2 kΩ, ∆ VO = 20V
110
eIN
Input Noise
IHF — A-Weighting Filter
2.0
dB
8
µV (max)
0.8
V (max)
2.5
V (min)
RIN = 600Ω (Input Referred)
Standby
VIL
Standby Low Input Voltage
Not in Standby Mode (Play)
VIH
Standby High Input Voltage
In Standby Mode
2.0
Mute
3
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LM4731
Absolute Maximum Ratings
LM4731
Electrical Characteristics (Notes 1, 2)
(Continued)
The following specifications apply for V+ = +22V, V- = −22V and RL = 8Ω unless otherwise specified. Limits apply for TA =
25˚C.
Symbol
Parameter
Conditions
VIL
Mute Low Input Voltage
Not in Mute Mode (Play)
VIH
Mute High Input Voltage
In Mute Mode
LM4731
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
0.8
V (max)
2.0
2.5
V (min)
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 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 a device’s performance.
Note 3: The maximum power dissipation must be de-rated at elevated temperatures and is dictated by TJMAX, θJC, and the ambient temperature TA. The maximum
allowable power dissipation is PDMAX = (TJMAX -TA) / θJC or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4731, TJMAX = 150˚C
and the typical θJC is 1.5˚C/W for the TA15A package . Refer to the Thermal Considerations section for more information.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Machine Model: a 220pF - 240pF discharged through all pins.
Note 6: Typical specifications are sepcified at 25˚C and represent the parametric norm.
Note 7: Tested limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 9: The operating junction temperature maximum is 150˚C. However, the instantaneous Safe Operating Area temperature is 250˚C.
Note 10: V- must have at least -9V at its pin with reference to GND in order for the under-voltage protection circuitry to be disabled. In addition, the voltage
differential between V+ and V- must be greater than 14V.
Note 11: The feedback compensation network limits the bandwidth of the closed-loop response causing the skew rate to be reduced by the high frequency roll-off.
Without feedback compensation the slew rate is typically larger.
Note 12: The LM4731TA package TA15A is a non-isolated package setting the tab of the device and the heat sink to V-potential when the LM4731TA is directly
mounted to the heat sink using only thermal compound. If a mica washer is used in addition to thermal compound, θCS (case to sink) is increased, but the heat sink
will be electrically isolated from V-.
Bridged Amplifier Application Circuit
20060305
FIGURE 2. Bridged Amplifier Application Circuit
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LM4731
Single Supply Application Circuit
20060306
FIGURE 3. Single Supply Amplifier Application Circuit
Note: *Optional components dependent upon specific design requirements.
Auxiliary Amplifier Application Circuit
20060307
FIGURE 4. Special Audio Amplifier Application Circuit
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LM4731
External Components Description
( See Figures 1 - 4 )
Components
Functional Description
1
RB
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.
2
Ri
Inverting input resistance to provide AC gain in conjunction with Rf.
3
Rf
Feedback resistance to provide AC gain in conjunction with Ri.
4
Ci
(Note 13)
Feedback capacitor which ensures unity gain at DC. Also creates a highpass filter with Ri at fC = 1/(2πRiCi).
5
CS
Provides power supply filtering and bypassing. Refer to the Supply Bypassing application section for proper
placement and selection of bypass capacitors.
6
RV
(Note 13)
Acts as a volume control by setting the input voltage level.
7
RIN
(Note 13)
Sets the amplifier’s input terminals DC bias point when CIN is present in the circuit. Also works with CIN to
create a highpass filter at fC = 1/(2πRINCIN). Refer to Figure 4.
8
CIN
(Note 13)
Input capacitor which blocks the input signal’s DC offsets from being passed onto the amplifier’s inputs.
9
RSN
(Note 13)
Works with CSN to stabilize the output stage by creating a pole that reduces high frequency instabilities.
10
CSN
(Note 13)
Works with RSN to stabilize the output stage by creating a pole that reduces high frequency instabilities. The
pole is set at fC = 1/(2πRSNCSN). Refer to Figure 4.
11
L (Note 13)
12
R (Note 13)
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.
13
RA
Provides DC voltage biasing for the transistor Q1 in single supply operation.
14
CA
Provides bias filtering for single supply operation.
15
RINP
(Note 13)
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 RINP.
16
RBI
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 RBI.
17
RE
Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the
half-supply point along with CA.
Note 13: Optional components dependent upon specific design requirements.
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LM4731
Typical Performance Characteristics
PSRR vs Frequency
± 22V, VRIPPLE = 1VRMS,
Supply Current vs
Supply Voltage
RL = 8Ω, 80kHz BW
20060368
20060365
THD+N vs Frequency
THD+N vs Frequency
± 18V, PO = 1W/Channel,
± 22V, PO = 1W/Channel,
RL = 4Ω, 80kHz BW
RL = 8Ω, 80kHz BW
20060369
20060370
THD+N vs Output Power
THD+N vs Output Power
± 18V, RL = 4Ω, 80kHz BW
± 22V, RL = 8Ω, 80kHz BW
20060371
20060372
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LM4731
Typical Performance Characteristics
(Continued)
Output Power vs
Supply Voltage
f = 1kHz, RL = 8Ω, 80kHz BW
Output Power vs
Supply Voltage
f = 1kHz, RL = 4Ω, 80kHz BW
20060363
20060364
Power Dissipation vs
Output Power
1% THD (max), RL = 8Ω, 80kHz BW
Power Dissipation vs
Output Power
1% THD (max), RL = 4Ω, 80kHz BW
20060361
20060362
Crosstalk vs Frequency
± 22V, PO = 10W,
RL = 8Ω, 80kHz BW
Crosstalk vs Frequency
± 18V, PO = 10W,
RL = 4Ω, 80kHz BW
20060373
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20060374
8
LM4731
Typical Performance Characteristics
(Continued)
Standby Attenuation vs
Standby Pin Voltage
± 22V, PO = 1W,
RL = 8Ω, 80kHz BW
Mute Attenuation vs
Mute Pin Voltage
± 22V, PO = 1W,
RL = 8Ω, 80kHz BW
20060360
20060366
Supply Current vs
Standby Pin Voltage
± 22V
20060367
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LM4731
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.
Application Information
MUTE MODE
By placing a logic-high voltage on the mute pins, the signal
going into the amplifiers will be muted. If the mute pins are
left floating or connected to a logic-low voltage, the amplifiers will be in a non-muted state. There are two mute pins,
one for each amplifier, so that one channel can be muted
without muting the other if the application requires such a
configuration. Refer to the Typical Performance Characteristics section for curves concerning Mute Attenuation vs
Mute Pin Voltage.
DETERMlNlNG MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understanding if optimum power output is to be obtained. An incorrect
maximum power dissipation calculation may result in inadequate heat sinking causing thermal shutdown and thus
limiting the output power.
Equation (1) exemplifies the theoretical maximum power
dissipation point of each amplifier where VCC is the total
supply voltage.
(1)
PDMAX = VCC2/2π2RL
STANDBY MODE
The standby mode of the LM4731 allows the user to drastically reduce power consumption when the amplifiers are
idle. By placing a logic-high voltage on the standby pins, the
amplifiers will go into Standby Mode. In this mode, the
current drawn from the VCC supply is typically less than 10
µA total for both amplifiers. The current drawn from the VEE
supply is typically 4.8mA. Clearly, there is a significant reduction in idle power consumption when using the standby
mode. There are two Standby pins, so that one channel can
be put in standby mode without putting the other amplifier in
standby if the application requires such flexibility. Refer to
the Typical Performance Characteristics section for
curves showing Supply Current vs. Standby Pin Voltage for
both supplies.
Thus by knowing the total supply voltage and rated output
load, the maximum power dissipation point can be calculated. The package dissipation is twice the number which
results from equation (1) since there are two amplifiers in
each LM4731. Refer to the graphs of Power Dissipation
versus Output Power in the Typical Performance Characteristics section which show the actual full range of power
dissipation not just the maximum theoretical point that results 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.
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection circuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning
on the LM4731 such that no DC output spikes occur. Upon
turn-off, the output of the LM4731 is brought to ground
before the power supplies such that no transients occur at
power-down.
The thermal resistance from the die (junction) to the outside
air (ambient) is a combination of three thermal resistances,
θJC, θCS, and θSA. In addition, the thermal resistance, θJC
(junction to case), of the LM4731TA is 1.5˚C/W. Using Thermalloy Thermacote thermal compound, the thermal resistance, θCS (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
temperature drops are analogous to voltage drops, the
power dissipation out of the LM4731 is equal to the following:
(2)
PDMAX = (TJMAX−TAMB)/θJA
where TJMAX = 150˚C, TAMB is the system ambient temperature and θJA = θJC + θCS + θSA.
Once the maximum package power dissipation has been
calculated using equation (1), the maximum thermal resistance, θSA, (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 θSA in equation (2).
θSA = [(TJMAX−TAMB)−PDMAX(θJC +θCS)]/PDMAX (3)
Again it must be noted that the value of θSA 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.
OVER-VOLTAGE PROTECTION
The LM4731 contains over-voltage protection circuitry that
limits the output current 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 alternately by sinking large current
spikes.
THERMAL PROTECTION
The LM4731 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die exceeds150˚C, the LM4731 shuts
down. It starts operating again when the die temperature
drops to about 145˚C, but if the temperature again begins to
rise, shutdown will occur again above 150˚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 between the thermal shutdown temperature limits of 150˚C and
145˚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 operation. Using the best heat sink possible within the cost and
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SUPPLY BYPASSING
The LM4731 has excellent power supply rejection and does
not require a regulated supply. However, to improve system
performance as well as eliminate possible oscillations, the
LM4731 should have its supply leads bypassed with lowinductance 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.
10
The LM4731 possesses a mute and standby function with
internal logic gates that are half-supply referenced. Thus, to
enable either the Mute or Standby function, the voltage at
these pins must be a minimum of 2.5V above half-supply. In
single-supply systems, devices such as microprocessors
and simple logic circuits used to control the mute and
standby functions, are usually referenced to ground, not
half-supply. Thus, to use these devices to control the logic
circuitry of the LM4731, a “level shifter,” like the one shown in
Figure 5, must be employed. A level shifter is not needed in
a split-supply configuration since ground is also half-supply.
(Continued)
These instabilities can be eliminated through multiple bypassing utilizing a large tantalum or electrolytic capacitor (10
µF or larger) which is used to absorb low frequency variations and a small ceramic capacitor (0.1 µF) 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 supplies be bypassed at the package terminals with an electrolytic capacitor of 470 µF or more.
BRIDGED AMPLIFIER APPLICATION
The LM4731 has two operational amplifiers internally, allowing for a few different amplifier configurations. One of these
configurations is referred to as “bridged mode” and involves
driving the load differentially through the LM4731’s outputs.
This configuration is shown in Figure 2. Bridged mode operation 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 configuration, 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 LM4731, which has two
operational amplifiers in one package, the package dissipation will increase by a factor of four. To calculate the
LM4731’s maximum power dissipation point for a bridged
load, multiply equation (1) by a factor of four.
This value of PDMAX can be used to calculate the correct size
heat sink for a bridged amplifier application. Since the internal dissipation for a given power supply and load is increased by using bridged-mode, the heatsink’s θSA 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 application.
20060354
FIGURE 5. Level Shift Circuit
When the voltage at the Logic Input node is 0V, the 2N3904
is “off” and thus resistor Rc pulls up mute or standby input to
the supply. This enables the mute or standby function. When
the Logic Input is 5V, the 2N3904 is “on” and consequently,
the voltage at the collector is essentially 0V. This will disable
the mute or standby function, and thus the amplifier will be in
its normal mode of operation. Rshift, along with Cshift, creates
an RC time constant that reduces transients when the mute
or standby functions are enabled or disabled. Additionally,
Rshift limits the current supplied by the internal logic gates of
the LM4731 which insures device reliability. Refer to the
Mute Mode and Standby Mode sections in the Application
Information section for a more detailed description of these
functions.
CLICKS AND POPS
In the typical application of the LM4731 as a split-supply
audio power amplifier, the IC exhibits excellent “click” and
“pop” performance when utilizing the mute and standby
modes. In addition, the device employs Under-Voltage Protection, which eliminates unwanted power-up and powerdown 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 application, the half-supply needs to charge up
just like the supply rail, VCC. 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
LM4731.
SINGLE-SUPPLY AMPLIFIER APPLICATION
The typical application of the LM4731 is a split supply amplifier. But as shown in Figure 3, the LM4731 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 LM4731
functions.
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LM4731
Application Information
LM4731
Application Information
instability and using the LM4731 for gains higher than 50V/V
will see an increase in noise and THD.
(Continued)
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 LM4731. In Figure 3, the resistor RINP
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 performance.
As shown in Figure 3, the resistors labeled RBI help bias up
the LM4731 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 RBI, namely 10 kΩ and 200 kΩ. 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.
The combination of Ri with Ci (see Figure 1) creates a high
pass filter. The low frequency response is determined by
these two components. The -3dB point can be found from
Equation (5) shown below:
(5)
fi = 1 / (2πRiCi) (Hz)
If an input coupling capacitor is used to block DC from the
inputs as shown in Figure 4, there will be another high pass
filter created with the combination of CIN and RIN. When
using a input coupling capacitor RIN is needed to set the DC
bias point on the amplifier’s input terminal. The resulting
-3dB frequency response due to the combination of CIN and
RIN can be found from Equation (6) shown below:
(6)
fIN = 1 / (2πRINCIN) (Hz)
PHYSICAL IC MOUNTING CONSIDERATIONS
Mounting of the TO-220 package to a heat sink must be
done such that there is sufficient pressure from the mounting
screw to insure good contact with the heat sink for efficient
heat flow. Over tightening the mounting screw will cause the
TO-220 package to warp reducing contact area with the heat
sink. Less contact with the heat sink will increase the thermal
resistance from the TO-220 package case to the heat sink
(θCS) resulting in higher operating die temperatures and
possible unwanted thermal shut down activation. Extreme
over tightening of the mounting screw will cause severe
physical stress resulting in cracked die and catastrophic IC
failure. The recommended maximum mounting screw torque
is 40 inch-lbs or 3.3 foot-lbs (4.5 newton-meter).
Additionally, if the mounting screw is used to force the TO220 package into correct alignment with the heat sink, package stress will be increased. This increase in package stress
will result in reduced contact area with the heat sink increasing die operating temperature and possible catastrophic IC
failure.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components is required to meet
the design targets of an application. The choice of external
component values that will affect gain and low frequency
response are discussed below.
The gain of each amplifier is set by resistors Rf and Ri for the
non-inverting configuration shown in Figure 1. The gain is
found by Equation (4) below:
(4)
AV = 1 + Rf / Ri (V/V)
For best noise performance, lower values of resistors are
used. A value of 1kΩ is commonly used for Ri and then
setting the value of Rf for the desired gain. For the LM4731
the gain should be set no lower than 10V/V and no higher
than 50V/V. Gain settings below 10V/V may experience
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LM4731
Application Information
(Continued)
20060355
FIGURE 6. Reference PCB Schematic
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LM4731
Application Information
(Continued)
LM4731 REFERENCE BOARD ARTWORK
Composite View
Silk Screen
20060356
20060357
Top Layer
Bottom Layer
20060358
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20060359
14
LM4731
Application Information
(Continued)
BILL OF MATERIALS FOR REFERENCE PCB
Symbol
Value
Tolerance
Type/Description
RIN1, RIN2
47kΩ
5%
1/4 Watt
RB1, RB2
1kΩ
1%
1/4 Watt
RF1, RF2
20kΩ
1%
1/4 Watt
Ri1, Ri2
1kΩ
1%
1/4 Watt
RSN1, RSN2
4.7Ω
5%
1/4 Watt
RG
2.7Ω
5%
1/4 Watt
CIN1, CIN2
1µF
10%
Metallized Polyester Film
Ci1, Ci2
47µF
20%
Electrolytic Radial / 35V
CSN1, CSN2
0.1µF
20%
Monolithic Ceramic
CV
0.1µF
20%
Monolithic Ceramic
CM
10µF
20%
Electrolytic Radial / 16V
CS1, CS2
0.1µF
20%
Monolithic Ceramic
CS3, CS4
10µF
20%
Electrolytic Radial / 35V
CS5, CS6
1,000µF
20%
Electrolytic Radial / 35V
S1, S2
SPDT (on-on) Switch
J 1, J 2
Non-switched PC Mount RCA Jack
J 4, J 7, J 8
PCB Banana Jack- BLACK
J 3, J 5, J 6, J 9
PCB Banana Jack- RED
U1
15 lead TO-220 Power Socket
U2
LM340, 5V Fixed Regulator, TO-263
package (TS3B)
15
Comments
www.national.com
LM4731 Stereo 25W Audio Power Amplifier with Mute and Standby Modes
Physical Dimensions
inches (millimeters) unless otherwise noted
Non-Isolated TO-220 15-Lead Package
Order Number LM4731TA
NS Package Number TA15A
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