LM4950
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LM4950 Boomer ™ Audio Power Amplifier Series 7.5W Mono-BTL or 3.1W Stereo Audio
Power Amplifier
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1FEATURES DESCRIPTION
The LM4950 is a dual audio power amplifier primarily
23• Pop & Click Circuitry Eliminates Noise During designed for demanding applications in flat panel
Turn-On and Turn-Off Transitions monitors and TV's. It is capable of delivering 3.1
• Low Current, Active-Low Shutdown Mode watts per channel to a 4Ωsingle-ended load with less
• Low Quiescent Current than 1% THD+N or 7.5 watts mono BTL to an 8Ω
load, with less than 10% THD+N from a 12VDC power
• Stereo 3.1W Output, RL= 4Ωsupply.
• Mono 7.5W BTL Output, RL= 8ΩBoomer audio power amplifiers were designed
• Short Circuit Protection specifically to provide high quality output power with a
• Unity-Gain Stable minimal amount of external components. The
• External Gain Configuration Capability LM4950 does not require bootstrap capacitors or
snubber circuits. Therefore, it is ideally suited for
display applications requiring high power and minimal
KEY SPECIFICATIONS size.
• Quiescent Power Supply Current 16mA (typ) The LM4950 features a low-power consumption
• POUT (SE) active-low shutdown mode. Additionally, the LM4950
– VDD = 12V, RL= 4Ω, 1% THD+N: 3.1W (typ) features an internal thermal shutdown protection
• POUT (BTL) mechanism along with short circuit protection.
– VDD = 12V, RL= 8Ω, 10% THD+N: 7.5W (typ) The LM4950 contains advanced pop & click circuitry
that eliminates noises which would otherwise occur
• Shutdown Current 40μA (typ) during turn-on and turn-off transitions.
APPLICATIONS The LM4950 is a unity-gain stable and can be
configured by external gain-setting resistors.
• Flat Panel Monitors
• Flat Panel TVs
• Computer Sound Cards
1Please 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.
2is a trademark of ~ Texas Instruments Incorporated.
3All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2003–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
VINA
SHUTDOWN
VOUTA
GND
VDD
VOUTB
BYPASS
VINB
2
3
4
5
6
7
8
9
1
GND (TAB)
VINA
SHUTDOWN
VOUTA
GND
GND (TAB)
VDD
VOUTB
BYPASS
VINB
LM4950
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Connection Diagrams
Figure 2. Plastic Package, DDPAK Figure 3. Plastic Package, TO-220
Top View Top View
See Package Number KTW0009A See Package Number NEC0009A
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)
Supply Voltage (pin 6, referenced to GND, pins 4 and 5) 18.0V
Storage Temperature −65°C to +150°C
pins 3 and 7 −0.3V to VDD + 0.3V
Input Voltage pins 1, 2, 8, and 9 −0.3V to 9.5V
Power Dissipation(4) Internally limited
Human Body Model(5) 2000V
ESD Susceptibility Machine Model(6) 200V
Junction Temperature 150°C
θJC (KTW) 4°C/W
θJA (KTW)(4) 20°C/W
Thermal Resistance θJC (NEC) 4°C/W
θJA (NEC)(4) 20°C/W
(1) All voltages are measured with respect to the GND pin, unless otherwise specified.
(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 ensure specific performance limits. Electrical Characteristics VDD = 12V 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 specified for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(4) The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,θJA, and the ambient temperature,
TA. The maximum allowable power dissipation is P DMAX = (TJMAX −TA) / θJA or the given in Absolute Maximum Ratings, whichever is
lower. For the LM4950 typical application (shown in Figure 1) with VDD = 12V, RL= 4Ωstereo operation the total power dissipation is
3.65W. θJA = 20°C/W for both DDPAK and TO220 packages mounted to 16in2heatsink surface area.
(5) Human body model, 100pF discharged through a 1.5 kΩresistor.
(6) Machine Model, 220pF–240pF discharged through all pins.
Operating Ratings
Temperature Range (TMIN ≤TA≤TMAX)−40°C ≤TA≤85°C
Supply Voltage 9.6V ≤VDD ≤16V
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Electrical Characteristics VDD = 12V(1)(2)
The following specifications apply for VDD = 12V, AV= 0dB (SE) or 6dB (BTL) unless otherwise specified. Limits apply for TA=
25°C.Symbol Parameter Conditions LM4950 Units
(Limits)
Typical(3) Limit(4)(5)
IDD Quiescent Power Supply Current VIN = 0V, IO= 0A, No Load 16 30 mA (max)
ISD Shutdown Current VSHUTDOWN = GND(6) 40 80 µA (max)
VOS Offset Voltage VIN = 0V, RL = 8Ω5 30 mV (max)
VSDIH Shutdown Voltage Input High 2.0 V (min)
VDD/2 V (max)
VSDIL Shutdown Voltage Input Low 0.4 V (max)
TWU Wake-up Time CB= 10µF 440 ms
150 °C (min)
TSD Thermal Shutdown Temperature 170 190 °C (max)
POOutput Power f = 1kHz
RL= 4ΩSE, Single Channel, THD+N 3.0 W (min)
= 1% 3.1
RL= 8ΩBTL, THD+N = 10% 7.5
PO= 2.5Wrms; f = 1kHz; 0.05
RL= 4ΩSE
THD+N Total Harmomic Distortion + Noise %
PO= 2.5Wrms; AV= 10; f = 1kHz; RL0.14
= 4Ω, SE
εOS Output Noise A-Weighted Filter, VIN = 0V, 10 µV
Input Referred
XTALK Channel Separation fIN = 1kHz, PO= 1W, SE Mode
RL= 8Ω76 dB
RL= 4Ω70
PSRR Power Supply Rejection Ratio VRIPPLE = 200mVp-p, f = 1kHz, 70 56 dB (min)
RL= 8Ω, BTL
IOL Output Current Limit VIN = 0V, RL= 500mΩ5 A
(1) All voltages are measured with respect to the GND pin, unless otherwise specified.
(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 ensure specific performance limits. Electrical Characteristics VDD = 12V 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 specified for parameters where no limit is given, however, the typical value is a good
indication of device performance.
(3) Typicals are measured at 25°C and represent the parametric norm.
(4) Limits are specified to AOQL (Average Outgoing Quality Level).
(5) Datasheet min/max specification limits are specified by design, test, or statistical analysis.
(6) Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to GND for
minimum shutdown current.
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Figure 4. Typical Stereo Single-Ended (SE) Audio Amplifier Application Circuit
External Components Description
See Figure 1.
Components Functional Description
This is the inverting input resistance that, along with RF, sets the closed-loop gain. Input resistance RIN and input
1. RIN capacitance CIN form a high pass filter. The filter's cutoff frequency is fc= 1/(2πRINCIN).
This is the input coupling capacitor. It blocks DC voltage at the amplifier's inverting input. CIN and RIN create a highpass
2. CIN filter. The filter's cutoff frequency is fC= 1/(2πRINCIN). Refer to SELECTING EXTERNAL COMPONENTS, for an
explanation of determining CIN's value.
3. RFThis is the feedback resistance that, along with Ri, sets closed-loop gain.
The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING for information about properly placing, and
4. CSselecting the value of, this capacitor.
This capacitor filters the half-supply voltage present on the BYPASS pin. Refer to SELECTING EXTERNAL
5. CBYPASS COMPONENTS for information about properly placing, and selecting the value of, this capacitor.
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Typical Performance Characteristics
THD+N vs Frequency THD+N vs Frequency
Figure 5. VDD = 12V, RL= 8ΩFigure 6. VDD = 12V, RL= 8Ω
BTL operation, POUT = 1W BTL operation, POUT = 3W
THD+N vs Frequency THD+N vs Frequency
Figure 7. VDD = 12V, RL= 8ΩFigure 8. VDD = 12V, RL= 8Ω
BTL operation, POUT = 5W BTL operation, BTLAV= 20, POUT = 1W
THD+N vs Frequency THD+N vs Frequency
Figure 9. VDD = 12V, RL= 8ΩFigure 10. VDD = 12V, RL= 8Ω
BTL operation, BTLAV= 20, POUT = 3W BTL operation, BTLAV= 20, POUT = 5W
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Typical Performance Characteristics (continued)
THD+N vs Frequency THD+N vs Frequency
Figure 11. VDD = 12V, RL= 4Ω, SE operation, Figure 12. VDD = 12V, RL= 4Ω, SE operation,
both channels driven and loaded (average shown), both channels driven and loaded (average shown),
POUT = 1W, AV= 1 POUT = 2.5W, AV= 1
THD+N vs Frequency THD+N vs Output Power
Figure 13. VDD = 12V, RL= 8Ω, SE operation, Figure 14. VDD = 12V, RL= 8Ω,
both channels driven and loaded (average shown), BTL operation, fIN = 1kHz
POUT = 1W, AV= 1
THD+N vs Output Power THD+N vs Output Power
Figure 15. VDD = 12V, RL= 8Ω, Figure 16. VDD = 12V, RL= 16Ω,
BTL operation, BTLAV= 20, fIN = 1kHz BTL operation, BTLAV= 20, fIN = 1kHz
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Typical Performance Characteristics (continued)
THD+N vs Output Power THD+N vs Output Power
Figure 17. VDD = 12V, RL= 4Ω, SE operation, Figure 18. VDD = 12V, RL= 8Ω, SE operation,
both channels driven and loaded (average shown), both channels driven and loaded (average shown),
fIN = 1kHz fIN = 1kHz
THD+N vs Output Power THD+N vs Output Power
Figure 19. VDD = 12V, RL= 16Ω, SE operation, Figure 20. VDD = 12V, RL= 4Ω, SE operation, AV= 10
both channels driven and loaded (average shown), both channels driven and loaded (average shown),
fIN = 1kHz fIN = 1kHz
THD+N vs Output Power Output Power vs Power Supply Voltage
Figure 21. VDD = 12V, RL= 8Ω, SE operation, AV= 10 Figure 22. RL= 8Ω, BTL, fIN = 1kHz,
both channels driven and loaded (average shown), at (from top to bottom at 12V):
fIN = 1kHz THD+N = 10 THD+N = 1%, THD+N = 0.2%
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Typical Performance Characteristics (continued)
Output Power vs Power Supply Voltage Output Power vs Power Supply Voltage
Figure 23. RL= 4Ω, SE operation, Figure 24. RL= 8Ω, SE operation, fIN = 1kHz,
both channels driven and loaded (average shown), both channels driven and loaded (average shown),
at (from top to bottom at 12V): THD+N = 10%, THD+N = 1% at (from top to bottom at 12V): THD+N = 10%, THD+N = 1%
Power Supply Rejection vs Frequency Power Supply Rejection vs Frequency
Figure 25. VDD = 12V, RL= 8Ω, BTL operation, Figure 26. VDD = 12V, RL= 8Ω, SE operation,
VRIPPLE = 200mVp-p, at (from top to bottom at 60Hz): VRIPPLE = 200mVp-p, at (from top to bottom at 60Hz):
CBYPASS = 1µF, CBYPASS = 4.7µF, CBYPASS = 10µF, CBYPASS = 1µF, CBYPASS = 4.7µF, CBYPASS = 10µF,
Power Supply Rejection vs Frequency Power Supply Rejection vs Frequency
Figure 27. VDD = 12V, RL= 8Ω, BTL operation, Figure 28. VDD = 12V, RL= 8Ω, SE operation,
VRIPPLE = 200mVp-p, VRIPPLE = 200mVp-p,
AV= 20, at (from top to bottom at 60Hz): AV= 10, at (from top to bottom at 60Hz):
CBYPASS = 1µF, CBYPASS = 4.7µF, CBYPASS = 10µF CBYPASS = 1µF, CBYPASS = 4.7µF, CBYPASS = 10µF
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Typical Performance Characteristics (continued)
Total Power Dissipation vs Load Dissipation Total Power Dissipation vs Load Dissipation
Figure 29. VDD = 12V, BTL operation, fIN = 1kHz, Figure 30. VDD = 12V, SE operation, fIN = 1kHz,
at (from top to bottom at 3W): RL= 8Ω, RL= 16Ωat (from top to bottom at 1W): RL= 4Ω, RL= 8Ω
Output Power vs Load Resistance Output Power vs Load Resistance
Figure 31. VDD = 12V, BTL operation, fIN = 1kHz, Figure 32. VDD = 12V, SE operation, fIN = 1kHz,
at (from top to bottom at 15Ω): THD+N = 10%, THD+N = 1% both channels driven and loaded, at (from top to bottom at
15Ω): THD+N = 10%, THD+N = 1%
Channel-to-Channel Crosstalk vs Frequency Channel-to-Channel Crosstalk vs Frequency
Figure 33. VDD = 12V, RL= 4Ω, POUT = 1W, SE operation, Figure 34. VDD = 12V, RL= 8Ω, POUT = 1W, SE operation,
VOUTA measured; VINA driven, VOUTB measured at (from top to bottom at 1kHz): VINB driven,
VOUTA measured; VINA driven, VOUTB measured
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Typical Performance Characteristics (continued)
THD+N vs Output Power THD+N vs Output Power
Figure 35. VDD = 9.6V, RL= 8Ω, Figure 36. VDD = 9.6V, RL= 4Ω, SE operation, fIN = 1kHz
BTL operation, fIN = 1kHz both channels driven and loaded (average shown)
THD+N vs Output Power THD+N vs Output Power
Figure 37. VDD = 9.6V, RL= 8Ω, BTL operation, Figure 38. VDD = 9.6V, RL= 4Ω, SE operation,
BTLAV= 20, fIN = 1kHz AV = 10, fIN = 1kHz
both channels driven and loaded (average shown)
Total Power Dissipation vs Load Dissipation Total Power Dissipation vs Load Dissipation per Channel
Figure 39. VDD = 9.6V, BTL operation, fIN = 1kHz Figure 40. VDD = 9.6V, SE operation, fIN = 1kHz,
at (from top to bottom at 2W): RL= 8Ω, RL= 16Ωat (from top to bottom at 1W): RL= 4Ω, RL= 8Ω
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Typical Performance Characteristics (continued)
Output Power vs Load Resistance Output Power vs Load Resistance
Figure 41. VDD = 9.6V, BTL operation, fIN = 1kHz, Figure 42. VDD = 9.6V, SE operation, fIN = 1kHz,
at (from top to bottom at 15Ω): THD+N = 10%, THD+N = 1% both channels driven and loaded, at (from top to bottom at
15Ω): THD+N = 10%, THD+N = 1%
Channel-to Channel Crosstalk vs Frequency Channel-to Channel Crosstalk vs Frequency
Figure 43. VDD = 9.6V, RL= 4Ω, POUT = 1W, SE operation, Figure 44. VDD = 9.6V, RL= 8Ω, POUT = 1W, SE operation,
at (from top to bottom at 1kHz): VINB driven, VOUTA at (from top to bottom at 1kHz):
measured; VINB driven, VOUTA measured;
VINA driven, VOUTB measured VINA driven, VOUTB measured
THD+N vs Output Power THD+N vs Output Power
Figure 45. VDD = 15V, RL= 8Ω, Figure 46. VDD = 15V, RL= 4Ω, SE operation,
BTL operation, fIN = 1kHz fIN = 1kHz both channels driven and loaded (average
shown)
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Typical Performance Characteristics (continued)
THD+N vs Output Power Total Power Dissipation vs Load Dissipation
Figure 47. VDD = 15V, RL= 8Ω, Figure 48. VDD = 15V, BTL operation, fIN = 1kHz,
SE operation, fIN = 1kHz at (from top to bottom at 4W): RL= 8Ω, RL= 16Ω
both channels driven and loaded (average shown)
Total Power Dissipation vs Load Dissipation per Channel Output Power vs Load Resistance
Figure 49. VDD = 15V, SE operation, fIN = 1kHz, Figure 50. VDD = 15V, BTL operation, fIN = 1kHz,
at (from top to bottom at 2W): at (from top to bottom at 15Ω):
RL= 4Ω, RL= 8ΩTHD+N = 10%, THD+N = 1%
Output Power vs Load Resistance THD+N vs Output Power
Figure 51. VDD = 15V, SE operation, fIN = 1kHz, Figure 52. VDD = 16V, RL= 8Ω,
both channels driven and loaded, BTL operation, fIN = 1kHz
at (from top to bottom at 15Ω):
THD+N = 10%, THD+N = 1%
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Typical Performance Characteristics (continued)
THD+N vs Output Power THD+N vs Output Power
Figure 53. VDD = 16V, RL= 8Ω, Figure 54. VDD = 16V, RL= 4Ω, AV= 10 SE operation,
BTL operation, fIN = 1kHz, BTLAV= 20 fIN = 1kHz, both channels driven and loaded
(average shown)
Channel-to-Channel Crosstalk vs Frequency Channel-to-Channel Crosstalk vs Frequency
Figure 55. VDD = 16V, RL= 4Ω, POUT = 1W, SE operation Figure 56. VDD = 16V, RL= 8Ω, POUT = 1W, SE operation
at (from top to bottom at 1kHz): VINB driven, at (from top to bottom at 1kHz): VINB driven,
VOUTA measured; VINA driven, VOUTB measured VOUTA measured; VINA driven, VOUTB measured
Power Supply Current vs Power Supply Voltage Power Supply Current vs Power Supply Voltage
Figure 57. RL= 8Ω, BTL operation VIN = 0V, RSOURCE = 50ΩFigure 58. RL= 4Ω, SE operation
VIN = 0V, RSOURCE = 50Ω
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Typical Performance Characteristics (continued)
Clipping Voltage vs Power Supply Voltage Clipping Voltage vs Power Supply Voltage
Figure 59. RL= 8Ω, BTL operation, fIN = 1kHz Figure 60. RL= 16Ω, BTL operation, fIN = 1kHz
at (from top to bottom at 12V): at (from to bottom at 12V):
positive signal swing, negative signal swing positive signal swing, negative signal swing
Clipping Voltage vs Power Supply Voltage Clipping Voltage vs Power Supply Voltage
Figure 61. RL= 4Ω, SE operation, fIN = 1kHz Figure 62. RL= 8Ω, SE operation, fIN = 1kHz
both channels driven and loaded, both channels driven and loaded,
at (from top to bottom at 13V): at (from to bottom at 13V):
negative signal swing, positive signal swing negative signal swing, positive signal swing
Power Dissipation vs Ambient Temperature Power Dissipation vs Ambient Temperature
Figure 63. VDD = 12V, RL= 8Ω(BTL), fIN = 1kHz, Figure 64. VDD = 12V, RL= 8Ω(SE), fIN = 1kHz,
(from to bottom at 80°C): (from to bottom at 120°C): 16in2copper plane heatsink area,
16in2copper plane heatsink area, 8in2copper plane heatsink area
8in2copper plane heatsink area
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APPLICATION INFORMATION
HIGH VOLTAGE BOOMER WITH INCREASED OUTPUT POWER
Unlike previous 5V Boomer amplifiers, the LM4950 is designed to operate over a power supply voltages range of
9.6V to 16V. Operating on a 12V power supply, the LM4950 will deliver 7.5W into an 8ΩBTL load with no more
than 10% THD+N.
Figure 65. Typical LM4950 BTL Application Circuit
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 65, the LM4950 consists of two operational amplifiers that drive a speaker connected
between their outputs. The value of external input and feedback resistors determine the gain of each amplifier.
Resistors RINAand RFAset the closed-loop gain of AMPA, whereas two 20kΩresistors set AMPB's gain to -1.
The LM4950 drives a load, such as a speaker, connected between the two amplifier outputs, VOUTAand
VOUTB.Figure 65 shows that AMPA's output serves as AMPB's input. This results in both amplifiers producing
signals identical in magnitude, but 180° out of phase. Taking advantage of this phase difference, a load is placed
between AMPAand AMPBand driven differentially (commonly referred to as "bridge mode"). This results in a
differential, or BTL, gain of
AVD = 2(Rf/Ri) (1)
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single
amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-
ended configuration: its differential output doubles the voltage swing across the load. Theoretically, this produces
four times the output power when compared to a single-ended amplifier under the same conditions. This increase
in attainable output power assumes that the amplifier is not current limited and that the output signal is not
clipped. To ensure minimum output signal clipping when choosing an amplifier's closed-loop gain, refer to AUDIO
POWER AMPLIFIER DESIGN.
Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by
biasing AMP1's and AMP2's outputs at half-supply. This eliminates the coupling capacitor that single supply,
single-ended amplifiers require. Eliminating an output coupling capacitor in a typical single-ended configuration
forces a single-supply amplifier's half-supply bias voltage across the load. This increases internal IC power
dissipation and may permanently damage loads such as speakers.
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POWER DISSIPATION
Power dissipation is a major concern when designing a successful single-ended or bridged amplifier. Equation 2
states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and
driving a specified output load.
PDMAX-SE = (VDD)2/(2π2RL): Single Ended (2)
The LM4950's dissipation is twice the value given by Equation 2 when driving two SE loads. For a 12V supply
and two 8ΩSE loads, the LM4950's dissipation is 1.82W.
The LM4950's dissipation when driving a BTL load is given by Equation 3. For a 12V supply and a single 8ΩBTL
load, the dissipation is 3.65W.
PDMAX-MONOBTL = 4(VDD)2/2π2RL: Bridge Mode (3)
The maximum power dissipation point given by Equation 3 must not exceed the power dissipation given by
Equation 4:
PDMAX' = (TJMAX - TA)/θJA (4)
The LM4950's TJMAX = 150°C. In the KTW package, the LM4950's θJA is 20°C/W when the metal tab is soldered
to a copper plane of at least 16in2. This plane can be split between the top and bottom layers of a two-sided
PCB. Connect the two layers together under the tab with a 5x5 array of vias. For the NEC package, use an
external heatsink with a thermal impedance that is less than 20°C/W. At any given ambient temperature TA, use
Equation 4 to find the maximum internal power dissipation supported by the IC packaging. Rearranging
Equation 4 and substituting PDMAX for PDMAX' results in Equation 5. This equation gives the maximum ambient
temperature that still allows maximum stereo power dissipation without violating the LM4950's maximum junction
temperature.
TA= TJMAX - PDMAX-MONOBTLθJA (5)
For a typical application with a 12V power supply and a BTL 8Ωload, the maximum ambient temperature that
allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately
77°C for the KTW package.
TJMAX = PDMAX-MONOBTLθJA + TA(6)
Equation 6 gives the maximum junction temperature TJMAX. If the result violates the LM4950's 150°C, reduce the
maximum junction temperature by reducing the power supply voltage or increasing the load resistance. Further
allowance should be made for increased ambient temperatures.
The above examples assume that a device is operating around the maximum power dissipation point. Since
internal power dissipation is a function of output power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation 3 is greater than that of Equation 4, then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further, ensure that speakers rated at a nominal 4Ω(SE
operation) or 8Ω(BTL operation) do not fall below 3Ωor 6Ω, respectively. If these measures are insufficient, a
heat sink can be added to reduce θJA. The heat sink can be created using additional copper area around the
package, with connections to the ground pins, supply pin and amplifier output pins. Refer to the Typical
Performance Characteristics curves for power dissipation information at lower output power levels.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding the voltage applied to any pin, with respect to
ground, as listed in Absolute Maximum Ratings section.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. Applications that employ a voltage regulator typically use a 10µF in parallel with a 0.1µF filter
capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient
response. However, their presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance
connected between the LM4950's supply pins and ground. Do not substitute a ceramic capacitor for the
tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between
the LM4950's power supply pin and ground as short as possible. Connecting a 10µF capacitor, CBYPASS, between
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the BYPASS pin and ground improves the internal bias voltage's stability and improves the amplifier's PSRR.
The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however, increases
turn-on time and can compromise the amplifier's click and pop performance. The selection of bypass capacitor
values, especially CBYPASS, depends on desired PSRR requirements, click and pop performance (as explained in
SELECTING EXTERNAL COMPONENTS), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4950 features an active-low micro-power shutdown mode. When active, the LM4950's micro-power
shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The low 40µA typical
shutdown current is achieved by applying a voltage to the SHUTDOWN pin that is as near to GND as possible. A
voltage that is greater than GND may increase the shutdown current.
There are a few methods to control the micro-power shutdown. These include using a single-pole, single-throw
switch (SPST), a microprocessor, or a microcontroller. When using a switch, connect a 100kΩpull-up resistor
between the SHUTDOWN pin and VDD and a second 100kΩresistor in parallel with the SPST switch connected
between the SHUTDOWN pin and GND. The two resistors form a voltage divider that ensures that the voltage
applied to the SHUTDOWN pin does not exceed VDD/2. Select normal amplifier operation by opening the switch.
Closing the switch applies GND to the SHUTDOWN pin, activating micro-power shutdown. The switch and
resistor ensure that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a
microprocessor or a microcontroller, use a digital output to apply the active-state voltage to the SHUTDOWN pin.
Again, ensure that the microcontroller or microprocessor logic-high signal does not exceed the LM4950's VDD/2
SHUTDOWN signal limit.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling capacitor: the lowest audio frequency that requires
amplification and desired output transient suppression.
As shown in Figure 65, the input resistor (RIN) and the input capacitor (CIN) produce a high pass filter cutoff
frequency that is found using Equation 7.
fc= 1/2πRiCi(7)
As an example when using a speaker with a low frequency limit of 50Hz, Ci, using Equation 7 is 0.159µF. The
0.39µF CINA shown in Figure 65 allows the LM4950 to drive high efficiency, full range speaker whose response
extends below 30Hz.
Bypass Capacitor Value
Besides minimizing the input capacitor size, careful consideration should be paid to value of CBYPASS, the
capacitor connected to the BYPASS pin. Since CBYPASS determines how fast the LM4950 settles to quiescent
operation, its value is critical when minimizing turn-on pops. The slower the LM4950's outputs ramp to their
quiescent DC voltage (nominally VDD/2), the smaller the turn-on pop. Choosing CBYPASS equal to 10µF along with
a small value of CIN (in the range of 0.1µF to 0.39µF), produces a click-less and pop-less shutdown function. As
discussed above, choosing CIN no larger than necessary for the desired bandwidth helps minimize clicks and
pops.
OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE
The LM4950 contains circuitry that eliminates turn-on and shutdown transients ("clicks and pops"). For this
discussion, turn-on refers to either applying the power supply voltage or when the micro-power shutdown mode
is deactivated.
As the VDD/2 voltage present at the BYPASS pin ramps to its final value, the LM4950's internal amplifiers are
configured as unity gain buffers and are disconnected from the AMPAand AMPBpins. An internal current source
charges the capacitor connected between the BYPASS pin and GND in a controlled manner. Ideally, the input
and outputs track the voltage applied to the BYPASS pin. The gain of the internal amplifiers remains unity until
the voltage applied to the BYPASS pin.
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The gain of the internal amplifiers remains unity until the voltage on the bypass pin reaches VDD/2. As soon as
the voltage on the bypass pin is stable, the device becomes fully operational and the amplifier outputs are
reconnected to their respective output pins. Although the BYPASS pin current cannot be modified, changing the
size of CBYPASS alters the device's turn-on time. Here are some typical turn-on times for various values of
CBYPASS:
CB(µF) TON (ms)
1.0 120
2.2 120
4.7 200
10 440
In order eliminate "clicks and pops", all capacitors must be discharged before turn-on. Rapidly switching VDD may
not allow the capacitors to fully discharge, which may cause "clicks and pops".
There is a relationship between the value of CIN and CBYPASS that ensures minimum output transient when power
is applied or the shutdown mode is deactivated. Best performance is achieved by setting the time constant
created by CIN and Ri+ Rfto a value less than the turn-on time for a given value of CBYPASS as shown in the table
above.
DRIVING PIEZO-ELECTRIC SPEAKER TRANSDUCERS
The LM4950 is able to drive capacitive piezo-electric transducer loads that are less than equal to 200nF. Stable
operation is assured by placing 33pF capacitors in parallel with the 20kΩfeedback resistors. The additional
capacitors are shown in Figure 66.
When driving piezo-electric tranducers, sound quality and accoustic power is entirely dependent upon a
transducer's frequency response and efficiency. In this application, power dissipated by the LM4950 is very low,
typically less than 250mW when driving a 200nF piezo-electric transduce (VDD = 12V).
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Figure 66. Piezo-electric Transducer Capacitance ≤200nF
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 4W into an 8ΩBTL
The following are the desired operational parameters:
Power Output 4WRMS
Load Impedance 8Ω
Input Level 0.3VRMS (max)
Input Impedance 20kΩ
Bandwidth 50Hz–20kHz ± 0.25dB
The design begins by specifying the minimum supply voltage necessary to obtain the specified output power.
One way to find the minimum supply voltage is to use the Output Power vs Power Supply Voltage curve in
Typical Performance Characteristics section. Another way, using Equation 8, is to calculate the peak output
voltage necessary to achieve the desired output power for a given load impedance. To account for the amplifier's
dropout voltage, two additional voltages, based on the Clipping Dropout Voltage vs Power Supply Voltage in
Typical Performance Characteristics, must be added to the result obtained by Equation 8. The result is
Equation 9.
(8)
VDD = VOUTPEAK + VODTOP + VODBOT (9)
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The Output Power vs. Power Supply Voltage graph in Typical Performance Characteristics for an 8Ωload
indicates a minimum supply voltage of 10.2V. The commonly used 12V supply voltage easily meets this. The
additional voltage creates the benefit of headroom, allowing the LM4950 to produce peak output power in excess
of 4W without clipping or other audible distortion. The choice of supply voltage must also not create a situation
that violates of maximum power dissipation as explained in the POWER DISSIPATION section. After satisfying
the LM4950's power dissipation requirements, the minimum differential gain needed to achieve 4W dissipation in
an 8ΩBTL load is found using Equation 10.
(10)
Thus, a minimum gain of 18.9 allows the LM4950's to reach full output swing and maintain low noise and THD+N
performance. For this example, let AV-BTL = 19. The amplifier's overall BTL gain is set using the input (RINA) and
feedback (R) resistors of the first amplifier in the series BTL configuration. Additionaly, AV-BTL is twice the gain set
by the first amplifier's RIN and Rf. With the desired input impedance set at 20kΩ, the feedback resistor is found
using Equation 11.
Rf/RIN = AV-BTL/2 (11)
The value of Rfis 190kΩ(choose 191kΩ, the closest value). The nominal output power is 4W.
The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired
±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth
limit. The gain variation for both response limits is 0.17dB, well within the ±0.25dB-desired limit. The results are
an fL= 50Hz / 5 = 10Hz (12)
and an
fL= 20kHz x 5 = 100kHz (13)
As mentioned in SELECTING EXTERNAL COMPONENTS, RINA and CINA create a highpass filter that sets the
amplifier's lower bandpass frequency limit. Find the coupling capacitor's value using Equation 14.
Ci= 1 /2πRINfL(14)
The result is
1/(2πx20kΩx10Hz) = 0.795µF (15)
Use a 0.82µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in this example) and the differential gain AVD,
determines the upper passband response limit. With AVD = 7 and fH= 100kHz, the closed-loop gain bandwidth
product (GBWP) is 700kHz. This is less than the LM4950's 3.5MHz GBWP. With this margin, the amplifier can
be used in designs that require more differential gain while avoiding performance restricting bandwidth
limitations.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figure 67 through Figure 69 show the recommended two-layer PC board layout that is optimized for the DDPAK-
packaged, SE-configured LM4950 and associated external components. Figure 70 through Figure 72 show the
recommended two-layer PC board layout that is optimized for the DDPAK-packaged, BTL-configured LM4950
and associated external components. These circuits are designed for use with an external 12V supply and
4Ω(min)(SE) or 8Ω(min)(BTL) speakers.
These circuit boards are easy to use. Apply 12V and ground to the board's VDD and GND pads, respectively.
Connect a speaker between the board's OUTAand OUTBoutputs.
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REVISION HISTORY
Changes from Revision D (May 2013) to Revision E Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 24
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PACKAGE OPTION ADDENDUM
www.ti.com 2-May-2013
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish MSL Peak Temp
(3)
Op Temp (°C) Top-Side Markings
(4)
Samples
LM4950TS ACTIVE DDPAK/
TO-263 KTW 9 45 TBD Call TI Call TI -40 to 85 L4950TS
LM4950TS/NOPB ACTIVE DDPAK/
TO-263 KTW 9 45 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 85 L4950TS
LM4950TSX/NOPB ACTIVE DDPAK/
TO-263 KTW 9 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 85 L4950TS
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM4950TSX/NOPB DDPAK/
TO-263 KTW 9 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
PACKAGE MATERIALS INFORMATION
www.ti.com 8-Nov-2013
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM4950TSX/NOPB DDPAK/TO-263 KTW 9 500 367.0 367.0 45.0
PACKAGE MATERIALS INFORMATION
www.ti.com 8-Nov-2013
Pack Materials-Page 2
MECHANICAL DATA
KTW0009A
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BOTTOM SIDE OF PACKAGE
TS9A (Rev B)
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