LM4755TSX/NOPB [TI]
LM4755 Stereo 11W Audio Power Amplifier with Mute;
| 型号： | LM4755TSX/NOPB |
| 厂家： | 
TEXAS INSTRUMENTS |
| 描述： | LM4755 Stereo 11W Audio Power Amplifier with Mute 放大器 商用集成电路 |
| 文件： | 总24页 (文件大小：953K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LM4755
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SNAS010E –FEBRUARY 1999–REVISED APRIL 2013
LM4755 Stereo 11W Audio Power Amplifier with Mute
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1
FEATURES
DESCRIPTION
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.
2
•
•
•
•
•
•
Drives 4Ω and 8Ω Loads
Integrated Mute Function
Internal Gain Resistors
Minimal External Components Needed
Single Supply Operation
Output power specifications at both 20V and 24V
supplies and low external component count offer high
value to consumer electronic manufacturers for
stereo TV and compact stereo applications. The
LM4755 is specifically designed for single supply
operation.
Internal Current Limiting and Thermal
Protection
•
•
Compact 9-lead TO-220 Package
Wide Supply Range 9V - 40V
APPLICATIONS
•
•
•
Stereos TVs
Compact Stereos
Mini Component Stereos
KEY SPECIFICATIONS
•
Output Power at 10% THD with 1kHz into 4Ω at
VCC = 24V 11 W (typ)
•
Output Power at 10% THD with 1kHz into 8Ω at
VCC = 24V 7 W (typ)
•
•
Closed Loop Gain 34 dB (typ)
PO at 10% THD+N @ 1kHz into 4Ω Single-
Ended DDPAK Package at VCC=12V 2.5 W (typ)
•
PO at 10% THD+N @ 1kHz into 8Ω Bridged
DDPAK Package at VCC=12V 5 W (typ)
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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LM4755
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TYPICAL APPLICATION
Figure 1. Typical Audio Amplifier Application Circuit
Connection Diagram
9 Pin TO-220
Plastic Package (Top View)
See Package Number NEC
9 Pin DDPAK
Plastic Package (Top View)
See Package Number KTW
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS(1)(2)(3)(4)
Supply Voltage
40V
±0.7V
Input Voltage
(5)
Input Voltage at Output Pins
GND -0.4V
Internally Limited
62.5W
Output Current
(6)
Power Dissipation
(7)
ESD Susceptibility
2 kV
Junction Temperature
Soldering Information
Storage Temperature
150°C
NEC Package (10 seconds)
250°C
−40°C to 150°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication
of device performance.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) The TO-263 Package is not recommended for VS > 16V due to impractical heatsinking limitations.
(4) All voltages are measured with respect to the GND pin (5), unless otherwse specified.
(5) The outputs of the LM4755 cannot be driven externally in any mode with a voltage lower than -0.4V below GND or permanent damage
to the LM4755 will result.
(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 = 2°C/W (junction to case). Refer to the section DETERMINING MAXIMUM POWER DISSIPATION in the
APPLICATION INFORMATION section for more information.
(7) Human body model, 100 pF discharged through a 1.5 kΩ resistor.
OPERATING RATINGS
Temperature Range TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +85°C
9V to 32V
Supply Voltage
θJC
θJA
2°C/W
76°C/W
ELECTRICAL CHARACTERISTICS
The following specifications apply to each channel with VCC = 24V, TA = 25°C unless otherwise specified.
LM4755
Typical(1)
Units
(Limits)
Symbol
ITOTAL
Parameter
Conditions
Limit
Total Quiescent Power
Supply Current
Mute Off
Mute On
10
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, DDPAK Pkg.
2.5
W
THD
Total Harmonic Distortion
Output Swing
f = 1 kHz, PO = 1 W/ch, RL = 8Ω
PO = 10W, RL = 8Ω
0.08
15
%
V
VOSW
PO = 10W, RL = 4Ω
14
V
XTALK
Channel Separation
See Apps. Circuit (Figure 1)
f = 1 kHz, VO = 4 Vrms
55
dB
(1) Typicals are measured at 25°C and represent the parametric norm.
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ELECTRICAL CHARACTERISTICS (continued)
The following specifications apply to each channel with VCC = 24V, TA = 25°C unless otherwise specified.
LM4755
Typical(1)
Units
(Limits)
Symbol
PSRR
Parameter
Conditions
Limit
Power Supply Rejection Ratio
See Apps. Circuit (Figure 1)
f = 120 Hz, VO = 1 mVrms
VIN = 0V
50
dB
VODV
Differential DC Output Offset
Voltage
0.09
0.4
V(max)
SR
Slew Rate
2
V/µs
kΩ
RIN
Input Impedance
83
65
34
PBW
AVCL
Power Bandwidth
3 dB BW at PO = 2.5W, RL = 8Ω
RL = 8Ω
kHz
Closed Loop Gain (Internally Set)
33
35
dB(min)
dB(max)
mVrms
εIN
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
2
A(min)
V(max)
Mute Pin
VIL
Not in Mute Mode
0.8
VIH
AM
Mute High Input Voltage
Mute Attenuation
In Mute Mode
VMUTE = 5.0V
2.0
80
2.5
V(min)
dB
EQUIVALENT SCHEMATIC
Figure 2.
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TEST CIRCUIT
Figure 3. Test Circuit
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SYSTEM APPLICATION CIRCUIT
Figure 4. 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.
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TYPICAL PERFORMANCE CHARACTERISTICS
Typicals are measured at 25°C and represent the parametric norm.
THD+N vs Output Power
THD+N vs Output Power
Figure 5.
Figure 6.
THD+N vs Output Power
THD+N vs Output Power
Figure 7.
Figure 8.
THD+N vs Output Power
THD+N vs Output Power
Figure 9.
Figure 10.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
THD+N vs Output Power
THD+N vs Output Power
Figure 11.
Figure 12.
THD+N vs Output Power
THD+N vs Output Power
Figure 13.
Figure 14.
THD+N vs Output Power
THD+N vs Output Power
Figure 15.
Figure 16.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
THD+N vs Output Power
THD+N vs Output Power
Figure 17.
Figure 18.
THD+N vs Output Power
THD+N vs Output Power
Figure 19.
Figure 20.
THD+N vs Output Power
THD+N vs Output Power
Figure 21.
Figure 22.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
THD+N vs Output Power
THD+N vs Output Power
Figure 23.
Figure 24.
THD+N vs Output Power
THD+N vs Output Power
Figure 25.
Figure 26.
THD+N vs Output Power
THD+N vs Output Power
Figure 27.
Figure 28.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
Output Power vs Supply Voltage
Output Power vs Supply Voltage
Figure 29.
Figure 30.
Frequency Response
THD+N vs Frequency
Figure 31.
Figure 32.
THD+N vs Frequency
Frequency Response
Figure 33.
Figure 34.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
Channel Separation
PSRR vs Frequency
Figure 35.
Figure 36.
Supply Current vs Supply Voltage
Power Derating Curve
Figure 37.
Figure 38.
Power Dissipation vs Output Power
Power Dissipation vs Output Power
Figure 39.
Figure 40.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Typicals are measured at 25°C and represent the parametric norm.
Power Dissipation vs Output Power
Power Dissipation vs Output Power
Figure 41.
Figure 42.
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APPLICATION INFORMATION
The LM4755 contains circuitry to pull down the bias line internally, effectively shutting down the input stage. An
external 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 towards 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.
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 mentioned earlier in the EXTERNAL COMPONENTS
DESCRIPTION section these capacitors create high-pass filters with their corresponding input/output
impedances. The Typical Application 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.
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.
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Figure 43. Bridge-Mode Application
Figure 44. THD+N vs POUT for Bridge-Mode Application
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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 operating 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 operating 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 requiring a high operating
supply voltage, with large supply and bias capacitors, and there is little or no other circuitry connected 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 45 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:
R = (0.7v) / (Cb • (VCC/2) / 0.1s)
(1)
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 Table 1 section for
more information.
Figure 45. 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 heatsink 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.
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The choice of a heatsink for a given application is dictated by several factors: the maximum power the IC needs
to dissipate, the worst-case ambient temperature of the circuit, the junction-to-case thermal resistance, and the
maximum junction 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
•
•
•
•
•
•
PDMAX = maximum power dissipation of the IC
TJ(°C) = junction temperature of the IC
TA(°C) = ambient temperature
θJC(°C/W) = junction-to-case thermal resistance of the IC
θCS(°C/W) = case-to-heatsink thermal resistance (typically 0.2 to 0.5 °C/W)
θSA(°C/W) = thermal resistance of heatsink
(2)
(3)
When determining the proper heatsink, the above equation should be re-written as:
θSA ≤ [(TJ–TA) / PDMAX] - θJC–θCS
DDPAK HEATSINKING
Surface mount applications will be limited by the thermal dissipation properties of printed circuit board area. The
DDPAK package is not recommended for surface mount applications with VS > 16V due to limited printed circuit
board area. There are DDPAK 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 approximate Thermal resistance (θSA) ranging from:
1.5 × 1.5 in. sq.
2 × 2 in. sq.
20–27°C/W
16–23°C/W
(TA=28°C, Sine wave
testing, 1 oz. Copper)
The above values for θSA vary widely due to dimensional proportions (i.e. variations in width and length will vary
θSA).
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 testing 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 limiting the undistorted power levels.
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:
(single channel)
PDMAX (W) = [VS2 / (2 • π2 • RL)]
The above equation is for a single channel class-AB power amplifier. For dual amplifiers such as the LM4755,
the equation for calculating the total maximum power dissipated is:
(dual channel)
PDMAX (W) = 2 • [VS2 / (2 • π2 • RL)]
or
VS2 / (π2 • RL)
(Bridged Outputs)
PDMAX (W) = 4[VS2 / (2π2 • RL)]
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HEATSINK DESIGN EXAMPLE
Determine the system parameters:
VS = 24V
RL = 4Ω
Operating Supply Voltage
Minimum Load Impedance
TA = 55°C
Worst Case Ambient Temperature
Device parameters from the datasheet:
TJ = 150°C
Maximum Junction Temperature
Junction-to-Case Thermal Resistance
θJC = 2°C/W
Calculations:
2 • PDMAX = 2 • [VS2 / 2 • π2 • RL)] = (24V)2 / (2 • π2 • 4Ω) = 14.6W
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.
DDPAK HEATSINK DESIGN EXAMPLES
Example 1:(Stereo Single-Ended Output)
Given: TA=30°C
TJ=150°C
RL=4Ω
VS=12V
θJC=2°C/W
PDMAX from PD vs PO Graph:
P
DMAX ≈ 3.7W
(4)
(5)
Calculating PDMAX
:
PDMAX = VCC2/(π2RL) = (12V)2/π2(4Ω)) = 3.65W
Calculating Heatsink Thermal Resistance:
θSA < TJ − TA / PDMAX − θJC − θCS
(6)
(7)
θSA < 120°C/3.7W − 2.0°C/W − 0.2°C/W = 30.2°C/W
Therefore the recommendation is to use 1.5 × 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
θJC=2°C/W
PDMAX from PD vs PO Graph:
P
DMAX ≈ 3.7W
(8)
(9)
Calculating PDMAX
:
PDMAX = VCC2/(π2RL)= (12V) 2/(π2(4Ω)) = 3.65W
Calculating Heatsink Thermal Resistance:
θSA < [(TJ − TA) / PDMAX] − θJC − θCS
(10)
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θSA < 100°C/3.7W − 2.0°C/W − 0.2°C/W = 24.8°C/W
(11)
Therefore the recommendation is to use 2.0 × 2.0 square inch of single-sided copper clad.
Example 3:(Bridged Output)
Given: TA=50°C
TJ=150°C
RL=8Ω
VS=12V
θJC=2°C/W
Calculating PDMAX
:
PDMAX = 4[VCC2/(2π2RL)] = 4(12V)2/(2π2(8Ω)) = 3.65W
(12)
Calculating Heatsink Thermal Resistance:
θSA < [(TJ − TA) / PDMAX] − θJC − θCS
(13)
(14)
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 × 2.0 square inch of single-sided copper clad.
LAYOUT AND GROUND RETURNS
Proper PC board layout is essential for good circuit performance. 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 possible to the IC.
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PC BOARD LAYOUT-COMPOSITE
Figure 46.
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PC BOARD LAYOUT-SILK SCREEN
Figure 47.
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PC BOARD LAYOUT-SOLDER SIDE
Figure 48.
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REVISION HISTORY
Changes from Revision D (April 2013) to Revision E
Page
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Changed layout of National Data Sheet to TI format .......................................................................................................... 22
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相关型号：
LM4765T/NOPB
IC 30 W, 2 CHANNEL, AUDIO AMPLIFIER, PZFM15, PLASTIC, TO-220, 15 PIN, Audio/Video Amplifier
NSC
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