LM4755_02 [NSC]
Stereo 11W Audio Power Amplifier with Mute; 立体声11W音频功率放大器静音
| 型号： | LM4755_02 |
| 厂家： | 
National Semiconductor |
| 描述： | Stereo 11W Audio Power Amplifier with Mute |
| 文件： | 总23页 (文件大小：789K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 2002
LM4755
Stereo 11W Audio Power Amplifier with Mute
@
n PO at 10% THD+N 1kHz into 8Ω bridged TO-263
General Description
package at VCC=12V: 5W (typ)
The LM4755 is a stereo audio amplifier capable of delivering
11W per channel of continuous average output power to a
4Ω load or 7W per channel into 8Ω using a single 24V supply
at 10% THD+N. The internal mute circuit and pre-set gain
resistors provide for a very economical design solution.
Features
n Drives 4Ω and 8Ω loads
n Integrated mute function
n Internal Gain Resistors
n Minimal external components needed
n Single supply operation
n Internal current limiting and thermal protection
n Compact 9-lead TO-220 package
n Wide supply range 9V - 40V
Output power specifications at both 20V and 24V supplies
and low external component count offer high value to con-
sumer electronic manufacturers for stereo TV and compact
stereo applications. The LM4755 is specifically designed for
single supply operation.
Key Specifications
n Output power at 10% THD with 1kHz into 4Ω at
VCC = 24V: 11W (typ)
Applications
n Stereos TVs
n Compact stereos
n Mini component stereos
n Output power at 10% THD with 1kHz into 8Ω at
VCC = 24V: 7W (typ)
n Closed loop gain: 34dB (typ)
@
n PO at 10% THD+N 1kHz into 4Ω single-ended
TO-263 package at VCC=12V: 2.5W (typ)
Typical Application
10005901
FIGURE 1. Typical Audio Amplifier Application Circuit
© 2004 National Semiconductor Corporation
DS100059
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Connection Diagrams
Plastic Package
10005902
Package Description
Top View
Order Number LM4755T
Package Number TA09A
10005936
Top View
Order Number LM4755TS
Package Number TS9A
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Absolute Maximum Ratings (Note 2)
T Package (10 seconds)
Storage Temperature
250˚C
−40˚C to 150˚C
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Ratings
Supply Voltage
40V
0.7V
Temperature Range
TMIN ≤ TA ≤ TMAX
Supply Voltage
θJC
Input Voltage
−40˚C ≤ TA ≤ +85˚C
9V to 32V
2˚C/W
Output Current
Internally Limited
62.5W
Power Dissipation (Note 3)
ESD Susceptability (Note 4)
Junction Temperature
Soldering Information
2 kV
θJA
76˚C/W
150˚C
Electrical Characteristics
The following specifications apply to each channel with VCC = 24V, TA = 25˚C unless otherwise specified.
LM4755
Units
Limit
Symbol
ITOTAL
Parameter
Conditions
Typical
(Note 5)
10
(Limits)
Total Quiescent Power
Supply Current
Mute Off
Mute On
15
7
mA(max)
mA(min)
mA
7
7
PO
Output Power (Continuous
Average per Channel)
f = 1 kHz, THD+N = 10%, RL = 8Ω
f = 1 kHz, THD+N = 10%, RL = 4Ω
VS = 20V, RL = 8Ω
W
11
4
10
W(min)
W
VS = 20V, RL = 4Ω
7
W
f = 1 kHz, THD+N = 10%, RL = 4Ω
VS = 12V, TO-263 Pkg.
f = 1 kHz, PO = 1 W/ch, RL = 8Ω
PO = 10W, RL = 8Ω
2.5
W
THD
Total Harmonic Distortion
Output Swing
0.08
15
%
V
VOSW
PO = 10W, RL = 4Ω
14
V
XTALK
PSRR
VODV
Channel Separation
See Apps. Circuit
55
dB
f = 1 kHz, VO = 4 Vrms
See Apps. Circuit
Power Supply Rejection Ratio
50
dB
f = 120 Hz, VO = 1 mVrms
VIN = 0V
Differential DC Output Offset
Voltage
0.09
0.4
V(max)
SR
Slew Rate
2
V/µs
kΩ
RIN
Input Impedance
Power Bandwidth
83
65
34
PBW
AVCL
3 dB BW at PO = 2.5W, RL = 8Ω
kHz
Closed Loop Gain (Internally Set) RL = 8Ω
33
35
dB(min)
dB(max)
mVrms
eIN
Noise
IHF-A Weighting Filter, RL = 8Ω
0.2
Output Referred
IO
Output Short Circuit Limit
Mute Low Input Voltage
VIN = 0.5V, RL = 2Ω
Not in Mute Mode
2
A(min)
V(max)
Mute Pin
VIL
0.8
VIH
Mute High Input Voltage
Mute Attenuation
In Mute Mode
VMUTE = 5.0V
2.0
80
2.5
V(min)
dB
AM
3
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Electrical Characteristics (Continued)
Note 1: All voltages are measured with respect to the GND pin (5), unless otherwse 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 device performance.
Note 3: 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 θ = 2˚C/W (junction to case). Refer to the section Determining the Maximum Power Dissipation in the Application Information section for more information.
JC
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Typicals are measured at 25˚C and represent the parametric norm.
Note 6: Limits are guaranteed that all parts are tested in production to meet the stated values.
>
Note 7: The TO-263 Package is not recommended for V
16V due to impractical heatsinking limitations.
S
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5
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Test Circuit
10005904
FIGURE 2. Test Circuit
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System Application Circuit
10005905
FIGURE 3. Circuit for External Components Description
External Components Description
Components
Function Description
Provides power supply filtering and bypassing.
1, 2
3, 4
5, 6
7
CS
RSN
CSN
Cb
Works with CSN to stabilize the output stage from high frequency oscillations.
Works with RSN to stabilize the output stage from high frequency oscillations.
Provides filtering for the internally generated half-supply bias generator.
8, 9
Ci
Input AC coupling capacitor which blocks DC voltage at the amplifier’s input terminals. Also creates a high
pass filter with fc=1/(2 • π • Rin • Cin).
10, 11
Co
Output AC coupling capacitor which blocks DC voltage at the amplifier’s output terminal. Creates a high
pass filter with fc=1/(2 • π • Rout • Cout).
12, 13
14
Ri
Voltage control - limits the voltage level allowed to the amplifier’s input terminals.
Works with Cm to provide mute function timing.
Rm
Cm
15
Works with Rm to provide mute function timing.
7
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Typical Performance Characteristics(Note 5)
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
10005912
10005913
10005906
10005908
THD+N vs Output Power
10005914
THD+N vs Output Power
10005907
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Typical Performance Characteristics(Note 5) (Continued)
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
10005915
10005916
10005909
10005911
THD+N vs Output Power
10005917
THD+N vs Output Power
10005910
9
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Typical Performance Characteristics(Note 5) (Continued)
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
10005938
10005939
10005941
10005943
THD+N vs Output Power
10005940
THD+N vs Output Power
10005942
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Typical Performance Characteristics(Note 5) (Continued)
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
THD+N vs Output Power
10005944
10005945
10005947
10005949
THD+N vs Output Power
10005946
THD+N vs Output Power
10005948
11
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Typical Performance Characteristics(Note 5) (Continued)
Output Power vs Supply Voltage
Output Power vs Supply Voltage
10005918
10005919
10005921
10005923
Frequency Response
THD+N vs Frequency
10005920
THD+N vs Frequency
Frequency Response
10005922
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Typical Performance Characteristics(Note 5) (Continued)
Channel Separation
PSRR vs Frequency
10005924
10005925
Supply Current vs Supply Voltage
Power Derating Curve
10005926
10005927
Power Dissipation vs Output Power
Power Dissipation vs Output Power
10005928
10005929
13
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Typical Performance Characteristics(Note 5) (Continued)
Power Dissipation vs Output Power
Power Dissipation vs Output Power
10005960
10005961
mentioned earlier in the External Components section
these capacitors create high-pass filters with their corre-
sponding input/output impedances. The Typical Applica-
tion Circuit shown in Figure 1 shows input and output
capacitors of 0.1 µF and 1,000 µF respectively. At the input,
with an 83 kΩ typical input resistance, the result is a high
pass 3 dB point occurring at 19 Hz. There is another high
pass filter at 39.8 Hz created with the output load resistance
of 4Ω. Careful selection of these components is necessary to
ensure that the desired frequency response is obtained. The
Frequency Response curves in the Typical Performance
Characteristics section show how different output coupling
capacitors affect the low frequency roll-off.
Application Information
The LM4755 contains circuitry to pull down the bias line
internally, effectively shutting down the input stage. An ex-
ternal R-C should be used to adjust the timing of the pull-
down. If the bias line is pulled down too quickly, currents
induced in the internal bias resistors will cause a momentary
DC voltage to appear across the inputs of each amplifier’s
internal differential pair, resulting in an output DC shift to-
wards Vsupply. An R-C timing circuit should be used to limit
the pull-down time such that output “pops” and signal
feedthroughs will be minimized. The pull-down timing is a
function of a number of factors, including the internal mute
circuitry, the voltage used to activate the mute, the bias
capacitor, the half-supply voltage, and internal resistances
used in the half-supply generator. Table 1 shows a list of
recommended values for the external R-C.
OPERATING IN BRIDGE-MODE
Though designed for use as a single-ended amplifier, the
LM4755 can be used to drive a load differentially (bridge-
mode). Due to the low pin count of the package, only the
non-inverting inputs are available. An inverted signal must
be provided to one of the inputs. This can easily be done with
the use of an inexpensive op-amp configured as a standard
inverting amplifier. An LF353 is a good low-cost choice. Care
must be taken, however, for a bridge-mode amplifier must
theoretically dissipate four times the power of a single-ended
type. The load seen by each amplifier is effectively half that
of the actual load being used, thus an amplifier designed to
drive a 4Ω load in single-ended mode should drive an 8Ω
load when operating in bridge-mode.
TABLE 1. Recommended Values for Mute Circuit
VMUTE
5V
VCC
12V
15V
20V
24V
28V
30V
Rm
Cm
18 kΩ
18 kΩ
12 kΩ
12 kΩ
8.2 kΩ
8.2 kΩ
10 µF
10 µF
10 µF
10 µF
10 µF
10 µF
5V
5V
5V
5V
5V
CAPACITOR SELECTION AND FREQUENCY
RESPONSE
With the LM4755, as in all single supply amplifiers, AC
coupling capacitors are used to isolate the DC voltage
present at the inputs (pins 3, 7) and outputs (pins 1, 8). As
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Application Information (Continued)
10005930
FIGURE 4. Bridge-Mode Application
10005931
10005937
FIGURE 5. THD+N vs POUT for Bridge-Mode Application
15
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Application Information (Continued)
PREVENTING OSCILLATIONS
With the integration of the feedback and bias resistors on-
chip, the LM4755 fits into a very compact package. However,
due to the close proximity of the non-inverting input pins to
the corresponding output pins, the inputs should be AC
terminated at all times. If the inputs are left floating, the
amplifier will have a positive feedback path through high
impedance coupling, resulting in a high frequency oscillation.
In most applications, this termination is typically provided by
the previous stage’s source impedance. If the application will
require an external signal, the inputs should be terminated to
ground with a resistance of 50 kΩ or less on the AC side of
the input coupling capacitors.
UNDERVOLTAGE SHUTDOWN
If the power supply voltage drops below the minimum oper-
ating supply voltage, the internal under-voltage detection
circuitry pulls down the half-supply bias line, shutting down
the preamp section of the LM4755. Due to the wide operat-
ing supply range of the LM4755, the threshold is set to just
under 9V. There may be certain applications where a higher
threshold voltage is desired. One example is a design requir-
ing a high operating supply voltage, with large supply and
bias capacitors, and there is little or no other circuitry con-
nected to the main power supply rail. In this circuit, when the
power is disconnected, the supply and bias capacitors will
discharge at a slower rate, possibly resulting in audible
output distortion as the decaying voltage begins to clip the
output signal. An external circuit may be used to sense for
the desired threshold, and pull the bias line (pin 6) to ground
to disable the input preamp. Figure 6 shows an example of
such a circuit. When the voltage across the zener diode
drops below its threshold, current flow into the base of Q1 is
interrupted. Q2 then turns on, discharging the bias capacitor.
This discharge rate is governed by several factors, including
the bias capacitor value, the bias voltage, and the resistor at
the emitter of Q2. An equation for approximating the value of
the emitter discharge resistor, R, is given below:
10005932
FIGURE 6. External Undervoltage Pull-Down
THERMAL CONSIDERATIONS
Heat Sinking
Proper heatsinking is necessary to ensure that the amplifier
will function correctly under all operating conditions. A heat-
sink that is too small will cause the die to heat excessively
and will result in a degraded output signal as the thermal
protection circuitry begins to operate.
The choice of a heatsink for a given application is dictated by
several factors: the maximum power the IC needs to dissi-
pate, the worst-case ambient temperature of the circuit, the
junction-to-case thermal resistance, and the maximum junc-
tion temperature of the IC. The heat flow approximation
equation used in determining the correct heatsink maximum
thermal resistance is given below:
TJ–TA = PDMAX • (θJC + θCS + θSA
where:
)
R = (0.7v) / (Cb • (VCC/2) / 0.1s)
PDMAX = maximum power dissipation of the IC
TJ(˚C) = junction temperature of the IC
TA(˚C) = ambient temperature
Note that this is only a linearized approximation based on a
discharge time of 0.1s. The circuit should be evaluated and
adjusted for each application.
As mentioned earlier in the Built-in Mute Circuit section,
when using an external circuit to pull down the bias line, the
rate of discharge will have an effect on the turn-off induced
distortions. Please refer to the Built-in Mute Circuit section
for more information.
θ
θ
JC(˚C/W) = junction-to-case thermal resistance of the IC
CS(˚C/W) = case-to-heatsink thermal resistance (typically
0.2 to 0.5 ˚C/W)
SA(˚C/W) = thermal resistance of heatsink
θ
When determining the proper heatsink, the above equation
should be re-written as:
θSA ≤ [(TJ–TA) / PDMAX] - θJC–θCS
TO-263 HEATSINKING
Surface mount applications will be limited by the thermal
dissipation properties of printed circuit board area. The TO-
263 package is not recommended for surface mount appli-
>
cations with VS
16V due to limited printed circuit board
area. There are TO-263 package enhancements, such as
clip-on heatsinks and heatsinks with adhesives, that can be
used to improve performance.
Standard FR-4 single-sided copper clad will have an ap-
proximate Thermal resistance (θSA) ranging from:
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PDMAX from PD vs PO Graph:
PDMAX ≈ 3.7W
Application Information (Continued)
1.5 x 1.5 in. sq.
2 x 2 in. sq.
20–27˚C/W (TA=28˚C, Sine wave
testing, 1 oz. Copper)
Calculating PDMAX
:
PDMAX = VCC2/(π2RL) = (12V)2/π2(4Ω)) = 3.65W
16–23˚C/W
Calculating Heatsink Thermal Resistance:
The above values for θSA vary widely due to dimensional
proportions (i.e. variations in width and length will vary θSA).
<
θSA TJ − TA / PDMAX − θJC − θCS
<
θSA 120˚C/3.7W − 2.0˚C/W − 0.2˚C/W = 30.2˚C/W
For audio applications, where peak power levels are short in
duration, this part will perform satisfactory with less
heatsinking/copper clad area. As with any high power design
proper bench testing should be undertaken to assure the
design can dissipate the required power. Proper bench test-
ing requires attention to worst case ambient temperature
and air flow. At high power dissipation levels the part will
show a tendency to increase saturation voltages, thus limit-
ing the undistorted power levels.
Therefore the recommendation is to use 1.5 x 1.5 square
inch of single-sided copper clad.
Example 2: (Stereo Single-Ended Output)
Given:
TA=50˚C
TJ=150˚C
RL=4Ω
VS=12V
θ
JC=2˚C/W
PDMAX from PD vs PO Graph:
PDMAX ≈ 3.7W
DETERMINING MAXIMUM POWER DISSIPATION
For a single-ended class AB power amplifier, the theoretical
maximum power dissipation point is a function of the supply
voltage, VS, and the load resistance, RL and is given by the
following equation:
Calculating PDMAX
:
PDMAX = VCC2/(π2RL)= (12V) 2/(π2(4Ω)) = 3.65W
(single channel)
PDMAX (W) = [VS / (2 • π2 • RL)]
Calculating Heatsink Thermal Resistance:
2
<
θSA [(TJ − TA) / PDMAX] − θJC − θCS
The above equation is for a single channel class-AB power
amplifier. For dual amplifiers such as the LM4755, the equa-
tion for calculating the total maximum power dissipated is:
<
θSA 100˚C/3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W
Therefore the recommendation is to use 2.0 x 2.0 square
inch of single-sided copper clad.
(dual channel)
PDMAX (W) = 2 • [VS / (2 • π2 • RL)]
Example 3: (Bridged Output)
2
Given:
TA=50˚C
TJ=150˚C
RL=8Ω
or
VS / (π2 • RL)
2
(Bridged Outputs)
PDMAX (W) = 4[VS / (2π2 • RL)]
VS=12V
2
θ
JC=2˚C/W
Calculating PDMAX
PDMAX = 4[VCC2/(2π2RL)] = 4(12V)2/(2π2(8Ω)) = 3.65W
:
HEATSINK DESIGN EXAMPLE
Determine the system parameters:
Calculating Heatsink Thermal Resistance:
VS = 24V
RL = 4Ω
Operating Supply Voltage
<
θSA [(TJ − TA) / PDMAX] − θJC − θCS
Minimum Load Impedance
Worst Case Ambient Temperature
<
θSA 100˚C / 3.7W − 2.0˚C/W − 0.2˚C/W = 24.8˚C/W
TA = 55˚C
Therefore the recommendation is to use 2.0 x 2.0 square
inch of single-sided copper clad.
Device parameters from the datasheet:
TJ = 150˚C
Maximum Junction Temperature
LAYOUT AND GROUND RETURNS
Proper PC board layout is essential for good circuit perfor-
mance. When laying out a PC board for an audio power
amplifier, particular attention must be paid to the routing of
the output signal ground returns relative to the input signal
and bias capacitor grounds. To prevent any ground loops,
the ground returns for the output signals should be routed
separately and brought together at the supply ground. The
input signal grounds and the bias capacitor ground line
should also be routed separately. The 0.1 µF high frequency
supply bypass capacitor should be placed as close as pos-
sible to the IC.
θJC = 2˚C/W
Junction-to-Case Thermal Resistance
Calculations:
2 • PDMAX = 2 • [VS / 2 • π2 • RL)] = (24V)2 / (2 • π2 • 4Ω)
= 14.6W
2
θSA ≤ [(TJ-TA) / PDMAX] - θJC–θCS = [ (150˚C - 55˚C) / 14.6W]
- 2˚C/W–0.2˚C/W = 4.3˚C/W
Conclusion: Choose a heatsink with θSA ≤ 4.3˚C/W.
TO-263 HEATSINK DESIGN EXAMPLES
Example 1: (Stereo Single-Ended Output)
Given:
TA=30˚C
TJ=150˚C
RL=4Ω
VS=12V
θ
JC=2˚C/W
17
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Application Information (Continued)
PC BOARD LAYOUT-COMPOSITE
10005933
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Application Information (Continued)
PC BOARD LAYOUT-SILK SCREEN
10005934
19
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Application Information (Continued)
PC BOARD LAYOUT-SOLDER SIDE
10005935
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Physical Dimensions inches (millimeters) unless otherwise noted
Order Number LM4755T
NS Package Number TA9A
21
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Order Number LM4755TS
NS Package Number TS9A
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Notes
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.
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