LM4873
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LM4873
SNAS033E – AUGUST 2000 – REVISED MAY 2013
Dual 2.1W Audio Amplifier Plus Stereo
Headphone Function
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FEATURES
DESCRIPTION
•
The LM4873 is a dual bridge-connected audio power
amplifier which, when connected to a 5V supply, will
deliver 2.1W to a 4Ω load or 2.4W to a 3Ω load with
less than 1.0% THD+N (see Notes below). In
addition, the headphone input pin allows the
amplifiers to operate in single-ended mode when
driving stereo headphones. A MUX control pin allows
selection between the two stereo sets of amplifier
inputs. The MUX control can also be used to select
two different closed-loop responses.
1
2
•
•
•
•
•
Input Mux Control and Two Separate Inputs
Per Channel
Stereo Headphone Amplifier Mode
“Click and Pop” Suppression Circuitry
Thermal Shutdown Protection Circuitry
PCB Area-Saving DSBGA and Thin DSBGA
Packages
TSSOP and HTSSOP and WQFN Packages
APPLICATIONS
•
•
•
Multimedia Monitors
Portable and Desktop Computers
Portable Audio Systems
KEY SPECIFICATIONS
•
•
•
•
PO at 1% THD+N
– LM4873LQ, 3Ω, 4Ω Loads 2.4W (typ), 2.1 W
(typ)
– LM4873MTE-1, 3Ω, 4Ω loads 2.4W (typ), 2.1
W (typ)
– LM4873IBL, 8Ω Load 1.1 W (typ)
– LM4873MTE, 4Ω 1.9 W (typ)
– LM4873, 8Ω 1.1 W (typ)
Single-Ended Mode THD+N at 75 mW Into
32Ω 0.5 % (max)
Shutdown Current 0.7 µA (typ)
Supply Voltage Range 2 to 5.5 V
Boomer audio power amplifiers were designed
specifically to provide high quality output power from
a surface mount package while requiring few external
components. To simplify audio system design, the
LM4873 combines dual bridge speaker amplifiers and
stereo headphone amplifiers on one chip.
The LM4873 features an externally controlled, lowpower consumption shutdown mode, a stereo
headphone amplifier mode, and thermal shutdown
protection. It also utilizes circuitry to reduce “clicks
and pops” during device turn-on.
Note:
An
LM4873MTE-1,
LM4873MTE,
or
LM4873LQ that has been properly mounted to a
circuit board will deliver 2.1W into 4Ω. The other
package options for the LM4873 will deliver 1.1W into
8Ω. See the APPLICATION INFORMATION sections
for further information concerning the LM4873MTE-1,
LM4873MTE, and the LM4873LQ.
Note:
An
LM4873MTE-1,
LM4873MTE,
or
LM4873LQ that has been properly mounted to a
circuit board and forced-air cooled will deliver 2.4W
into 3Ω.
1
2
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.
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.
Copyright © 2000–2013, Texas Instruments Incorporated
LM4873
SNAS033E – AUGUST 2000 – REVISED MAY 2013
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Connection Diagrams
Figure 1. Top View
See Package Number PWP0028A
for Exposed-DAP HTSSOP
Figure 2. Top View
See Package Number PW0020A for TSSOP
See Package Number PWP0020A
for Exposed-DAP HTSSOP
Figure 3. Top View
See Package Number NHW0024A
for Exposed-DAP WQFN
Figure 4. Top View
(Bump-side down)
See Package Number BLA20AAB for DSBGA
See Package Number YZR0020AAA
LM4873IBP PIN DESIGNATIONS
2
Pin (Bump) Number
Pin (Bump) Function
Pin (Bump) Number
Pin (Bump) Function
A1
-IN A1
C3
VDD
A2
-IN A2
C4
+IN B
A3
-IN B2
D1
+OUT A
A4
-IN B1
D2
GND
B1
-OUT A
D3
GND
B2
GND
D4
+OUT B
B3
GND
E1
MUX CTRL
SHUTDOWN
B4
-OUT B
E2
C1
+IN A
E3
HP-IN
C2
VDD
E4
BYPASS
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Typical Application
Note: Pin out shown for the 28-pin Exposed-DAP HTSSOP package. Refer to the Connection Diagrams for the pin
out of the 20-pin Exposed-DAP HTSSOP, Exposed-DAP WQFN, and DSBGA packages.
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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)
Supply Voltage
6.0V
−65°C to +150°C
Storage Temperature
−0.3V to VDD +0.3V
Input Voltage
Power Dissipation
(3)
Internally limited
ESD Susceptibility
(4)
2000V
ESD Susceptibility
(5)
200V
Junction Temperature
Solder Information
150°C
SOIC Package
Vapor Phase (60 sec.)
215°C
Infrared (15 sec.)
220°C
θJC (typ)—PW0020A
20°C/W
θJA (typ)—PW0020A
80°C/W
θJC (typ)—PWP0020A
Thermal Resistance
41°C/W
(6)
θJA (typ)—PWP0020A
51°C/W
(7)
θJA (typ)—PWP0020A
90°C/W
(8)
θJC (typ)—PWP0028A
θJA (typ)—PWP0028A
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
2°C/W
41°C/W
(9)
θJA (typ)—PWP0028A
51°C/W
(10)
θJA (typ)—PWP0028A
90°C/W
(11)
θJC (typ)—NHW0024A
(1)
2°C/W
θJA (typ)—PWP0020A
3.0°C/W
θJA (typ)—NHW0024A
42°C/W
(12)
θJA (typ)—DSBGA
60°C/W
(13)
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
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 operates within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given. The typical value however, is a good indication
of device performance.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θ JA, and the ambient temperature
TA. The maximum allowable power dissipation is PDMAX = (TJMAX − T A)/θJA. For the LM4873, TJMAX = 150°C. For the θJAs for different
packages, please see the APPLICATION INFORMATION section or the Absolute Maximum Ratings section.
Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Machine model, 220 pF–240 pF discharged through all pins.
The given θJA is for an LM4873 packaged in an PWP0020A with the Exposed-DAP soldered to an exposed 2in2 area of 1oz printed
circuit board copper.
The given θJA is for an LM4873 packaged in an PWP0020A with the Exposed-DAP soldered to an exposed 1in2 area of 1oz printed
circuit board copper.
The given θJA is for an LM4873 packaged in an PWP0020A with the Exposed-DAP not soldered to printed circuit board copper.
The given θJA is for an LM4873 packaged in an PWP0028A with the Exposed-DAP soldered to an exposed 2in2 area of 1oz printed
circuit board copper.
The given θJA is for an LM4873 packaged in an PWP0028A with the Exposed-DAP soldered to an exposed 1in2 area of 1oz printed
circuit board copper.
The given θJA is for an LM4873 packaged in an PWP0028A with the Exposed-DAP not soldered to printed circuit board copper.
The given θJA is for an LM4873 packaged in an NHW0024A with the Exposed-DAP soldered to an exposed 2in2 area of 1oz printed
circuit board copper.
The θJA is specified for an LM4873 packaged in a BLA20AAB or YZR0020AAA with their four ground connections soldered to a 3in2,
1oz copper plane.
OPERATING RATINGS
Temperature Range
TMIN ≤ TA ≤ TMAX
4
−40°C ≤ TA ≤ 85°C
2.0V ≤ VDD ≤ 5.5V
Supply Voltage
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ELECTRICAL CHARACTERISTICS
(1) (2)
The following specifications apply for VDD= 5V unless otherwise noted. Limits apply for TA= 25°C.
Symbol
Parameter
Conditions
LM4873
Typical
VDD
Supply Voltage
IDD
Quiescent Power Supply Current
ISD
Shutdown Current
VIH
VIL
(1)
(2)
(3)
(4)
(5)
(3)
Limit
Units
(Limits)
(4)
2
V (min)
5.5
V (max)
mA (max)
VIN = 0V, IO = 0A
(5)
, HP-IN = 0V
7.5
15
VIN = 0V, IO = 0A
(5)
, HP-IN = 4V
5.8
6
mA (min)
0.7
2
μA (max)
Headphone High Input Voltage
4
V (min)
Headphone Low Input Voltage
0.8
V (max)
VDD applied to the SHUTDOWN pin
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 operates within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given. The typical value however, is a good indication
of device performance.
All voltages are measured with respect to the ground (GND) pins, unless otherwise specified.
Typicals are specified at 25°C and represent the parametric norm.
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
ELECTRICAL CHARACTERISTICS FOR BRIDGED-MODE OPERATION
(1) (2)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25°C.
Symbol
Parameter
Conditions
LM4873
Typical
VOS
Output Offset Voltage
VIN = 0V
5
THD+N = 1%, f = 1kHz
PO
Output Power
(6)
(5)
THD+N = 10%, f = 1kHz
(6)
(2)
(3)
(4)
(5)
(6)
Limit
50
(4)
Units
(Limits)
mV
(max)
LM4873MTE-1, RL = 3Ω
2.4
W
LM4873MTE, RL = 3Ω
2.2
W
LM4873LQ, RL = 3Ω
2.2
W
LM4873MTE-1, RL = 4Ω
2.1
W
LM4873MTE, RL = 4Ω
1.9
W
LM4873LQ, RL = 4Ω
1.9
W
LM4873MT, RL = 4Ω
1.9
W
LM4873, RL = 8Ω
1.1
LM4873MTE-1, RL = 3Ω
3.0
W
LM4873LQ, RL = 3Ω
3.0
W
LM4873MTE-1, RL = 4Ω
2.6
W
LM4873LQ, RL = 4Ω
2.6
W
LM4873, RL = 8Ω
1.5
W
0.34
W
THD+N = 1%, f = 1kHz, RL = 32Ω
(1)
(3)
1.0
W (min)
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 operates within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given. The typical value however, is a good indication
of device performance.
All voltages are measured with respect to the ground (GND) pins, unless otherwise specified.
Typicals are specified at 25°C and represent the parametric norm.
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
Output power is measured at the device terminals.
When driving 3Ω or 4Ω loads and operating on a 5V supply, the LM4873LQ must be mounted to a circuit board that has a minimum of
2.5in2 of exposed, uninterrupted copper area connected to the WQFN package's exposed DAP.
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ELECTRICAL CHARACTERISTICS FOR BRIDGED-MODE OPERATION (1) (2) (continued)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25°C.
Symbol
Parameter
Conditions
LM4873
Typical
THD+N
(3)
Limit
(4)
Units
(Limits)
LM4873MTE-1, RL = 4Ω, PO =
2W
Total Harmonic
Distortion+Noise
20Hz ≤ f ≤ 20kHz, AVD = 2
PSRR
Power Supply Rejection
Ratio
XTALK
SNR
LM4873LQ, RL = 4Ω, PO =
2W
0.3
%
VDD = 5V, VRIPPLE = 200mVRMS, RL = 8Ω, CB = 1.0μF
67
dB
Channel Separation
f = 1kHz, CB = 1.0μF
80
dB
Signal To Noise Ratio
VDD = 5V, PO = 1.1W, RL = 8Ω
97
dB
LM4873, RL = 8Ω, PO = 1W
ELECTRICAL CHARACTERISTICS FOR SINGLE-ENDED OPERATION
(1) (2) (3)
The following specifications apply for VDD= 5V unless otherwise specified. Limits apply for TA= 25°C.
Symbol
Parameter
Conditions
LM4873
Typical (4)
VOS
Output Offset Voltage
PO
Output Power
VIN = 0V
Limit
(5)
Units
(Limits)
5
50
mV (max)
THD+N = 0.5%, f = 1 kHz, RL = 32Ω
85
75
mW (min)
THD+N = 1%, f = 1 kHz, RL = 8Ω
340
mW
THD+N = 10%, f = 1 kHz, RL = 8Ω
440
mW
THD+N
Total Harmonic Distortion+Noise
AV = −1, PO = 75mW, 20Hz ≤ f ≤ 20kHz, RL = 32Ω
0.2
%
PSRR
Power Supply Rejection Ratio
CB = 1.0μF, VRIPPLE = 200mV RMS, f = 1kHz
52
dB
XTALK
Channel Separation
f = 1kHz, CB = 1.0μF
60
dB
SNR
Signal To Noise Ratio
VDD = 5V, PO = 340mW, RL = 8Ω
94
dB
(1)
(2)
(3)
(4)
(5)
6
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 operates within the
Operating Ratings. Specifications are not ensured for parameters where no limit is given. The typical value however, is a good indication
of device performance.
All voltages are measured with respect to the ground (GND) pins, unless otherwise specified.
Refer to Figure 1
Typicals are specified at 25°C and represent the parametric norm.
Datasheet min/max specification limits are ensured by design, test, or statistical analysis.
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TYPICAL PERFORMANCE CHARACTERISTICS MTE (20-PIN) AND LQ (24-PIN) SPECIFIC
CHARACTERISTICS
LM4873MTE, LM4873LQ THD+N vs Output Power
LM4873MTE, LM4873LQ THD+N vs Frequency
Figure 5.
Figure 6.
LM4873MTE, LM4873LQ THD+N vs Output Power
LM4873MTE, LM4873LQ Power Dissipation vs Power Output
Figure 7.
Figure 8.
LM4873MTE Power Derating Curve
LM4873LQ Power Derating Curve
Figure 9.
Figure 10.
Figure 9 shows the LM4873MTE's and the LM4873LQ's thermal dissipation ability at different ambient temperatures
given these conditions: 500LFPM + JEDEC board: The part is soldered to a 1S2P 20-lead exposed-DAP HTSSOP
test board with 500 linear feet per minute of forced-air flow across it.Board information - copper dimensions:
74x74mm, copper coverage: 100% (buried layer) and 12% (top/bottom layers), 16 vias under the exposed-DAP.
500LFPM + 2.5in2: The part is soldered to a 2.5in2, 1 oz. copper plane with 500 linear feet per minute of forced-air
flow across it. 2.5in2: The part is soldered to a 2.5in2, 1oz. copper plane. Not Attached: The part is not soldered
down and is not forced-air cooled.
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TYPICAL PERFORMANCE CHARACTERISTICS MTE-1 (28 PIN) SPECIFIC CHARACTERISTICS
LM4873MTE-1
THD+N vs Output Power
LM4873MTE-1
THD+N vs Frequency
Figure 11.
Figure 12.
LM4873MTE-1
THD+N vs Output Power
LM4873MTE-1
THD+N vs Frequency
Figure 13.
Figure 14.
LM4873MTE-1
Power Dissipation vs Power Output
LM4873MTE-1
Power Derating Curve
Figure 15.
Figure 16.
Figure 15 shows the LM4835MTE-1's thermal dissipation ability at different ambient temperatures given these
conditions: 500LFPM + 2in2: The part is soldered to a 2in2, 1 oz. copper plane with 500 linear feet per minute of
forced-air flow across it. 2in2on bottom: The part is soldered to a 2in2, 1oz. copper plane that is on the bottom side
of the PC board through 21 8 mil vias.2in2: The part is soldered to a 2in2, 1oz. copper plane. 1in2: The part is
soldered to a 1in2, 1oz. copper plane. Not Attached: The part is not soldered down and is not forced-air cooled.
8
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TYPICAL PERFORMANCE CHARACTERISTICS
THD+N vs Frequency
THD+N vs Frequency
Figure 17.
Figure 18.
THD+N vs Frequency
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)
10
THD+N vs Output Power
THD+N vs Frequency
Figure 23.
Figure 24.
THD+N vs Output Power
THD+N vs Frequency
Figure 25.
Figure 26.
Output Power vs Load Resistance
Power Dissipation vs Supply Voltage
Figure 27.
Figure 28.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Output Power vs Supply Voltage
Output Power vs Supply Voltage
Figure 29.
Figure 30.
Output Power vs Supply Voltage
Output Power vs Load Resistance
Figure 31.
Figure 32.
Output Power vs Load Resistance
LM4873IBL
Stereo Output Power vs Power Dissipation
Figure 33.
Figure 34.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
12
Power Dissipation vs Output Power
Dropout Voltage vs Supply Voltage
Figure 35.
Figure 36.
Power Derating Curve
Power Dissipation vs Output Power
Figure 37.
Figure 38.
Noise Floor
Channel Separation
Figure 39.
Figure 40.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Channel Separation
Power Supply Rejection Ratio
Figure 41.
Figure 42.
Open Loop Frequency Response
Supply Current vs Supply Voltage
Figure 43.
Figure 44.
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Table 1. External Components Description
Components
Functional Description
1.
Ri
The inverting input resistance, along with Rf, set the closed-loop gain. Ri, along with Ci, form a high pass filter with fc =
1/(2πRiCi).
2.
Ci
The input coupling capacitor blocks DC voltage at the amplifier's input terminals. Ci, along with Ri, create a highpass filter
with fc = 1/(2πRiCi). Refer to the section, SELECTING PROPER EXTERNAL COMPONENTS, for an explanation of
determining the value of Ci.
3.
Rf
The feedback resistance, along with Ri, set the closed-loop gain.
4.
Cs
The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about properly placing,
and selecting the value of, this capacitor.
5.
CB
The capacitor, CB, filters the half-supply voltage present on the BYPASS pin. Refer to the SELECTING PROPER
EXTERNAL COMPONENTS section for information concerning proper placement and selecting CB's value.
APPLICATION INFORMATION
LM4863 PIN CONFIGURATION COMPATIBILITY
The LM4873's pin configuration simplifies the process of upgrading systems that use the LM4863. Except for its
four MUX function pins, the LM4873's pin configuration matches the LM4863's pin configuration. If the LM4873's
MUX functionality is not needed when replacing an LM4863, connect the MUX CTRL pin to either VDD or ground.
As shown in Table 2, grounding the MUX CTRL pin selects stereo input 1 (–IN A1 and –IN B1), whereas
applying VDD to the MUX CTRL pin selects stereo input 2 (–IN A2 and –IN B2).
STEREO-INPUT MULTIPLEXER (STEREO MUX)
Typical LM4873 applications use the MUX to switch between two stereo input signals. Each stereo channel's
gain can be tailored to produce the required output signal level. Choosing the input and feedback resistor ratio
sets a MUX channel's gain. Another configuration uses the MUX to select two different gains or frequency
compensated gains to amplify a single pair of stereo input signals. Figure 45 shows two different feedback
networks, Network 1 and Network 2. Network 1 produces increasing gain as the input signal's frequency
decreases. This can be used to compensate a small, full-range speaker's low frequency response roll-off.
Network 2 sets the gain for an alternate load such as headphones. Connecting the MUX CTRL and HP-IN pins
together applies the same control voltage to the MUX pins when connecting and disconnecting headphones
using the headphone jack shown in Figure 46 or Figure 47. Simultaneously applying the control voltage
automatically selects the amplifier (headphone or bridge loads) and switches the gain (MUX channel selection).
Alternatively, leave the control pins independently accessible. This allows a user to select bass boost as needed.
This alternative user-selectable bass-boost scheme requires connecting equal ratio resistor feedback networks to
each MUX input channel. The value of the resistor in the RC network is chosen to give a gain that is necessary
to achieve the desired bass-boost.
Switching between the MUX channels may change the input signal source or the feedback resistor network.
During the channel switching transition, the average voltage level present on the internal amplifier's input may
change. This change can slew at a rate that may produce audible voltage transients or clicks in the amplifier's
output signal. Using the MUX to select between two vastly dissimilar gains is a typical transient-producing
situation. As the MUX is switched, an audible click may occur as the gain suddenly changes.
14
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Figure 45. Input MUX Example
DSBGA PACKAGE PCB MOUNTING CONSIDERATIONS
PCB layout specifications unique to the LM4873's DSBGA package are found in Texas Instruments' AN-1112
(literature number SNVA009).
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS
The LM4873's exposed-DAP (die attach paddle) packages (MTE, MTE-1, LQ) provide a low thermal resistance
between the die and the PCB to which the part is mounted and soldered. This allows rapid heat transfer from the
die to the surrounding PCB copper traces, ground plane and, finally, surrounding air. The result is a low voltage
audio power amplifier that produces 2.1W at ≤ 1% THD with a 4Ω load. This high power is achieved through
careful consideration of necessary thermal design. Failing to optimize thermal design may compromise the
LM4873's high power performance and activate unwanted, though necessary, thermal shutdown protection.
The MTE, MTE-1, and LQ packages must have their DAPs soldered to a copper pad on the PCB. The DAP's
PCB copper pad is connected to a large plane of continuous unbroken copper. This plane forms a thermal mass
and heat sink and radiation area. Place the heat sink area on either outside plane in the case of a two-sided
PCB, or on an inner layer of a board with more than two layers. Connect the DAP copper pad to the inner layer
or backside copper heat sink area with 32(4x8) ( (MTE), 40(4x10) (MTE-1), or 6(3x2) (LQ) vias. The via diameter
should be 0.012in–0.013in with a 1.27mm pitch. Ensure efficient thermal conductivity by plating-through and
solder-filling the vias.
Best thermal performance is achieved with the largest practical copper heat sink area. If the heatsink and
amplifier share the same PCB layer, a nominal 2.5in2 (min) area is necessary for 5V operation with a 4Ω load.
Heatsink areas not placed on the same PCB layer as the LM4873 should be 5in2 (min) for the same supply
voltage and load resistance. The last two area recommendations apply for 25°C ambient temperature. Increase
the area to compensate for ambient temperatures above 25°C. In systems using cooling fans, the LM4873MTE
can take advantage of forced air cooling. With an air flow rate of 450 linear-feet per minute and a 2.5in2 exposed
copper or 5.0in2 inner layer copper plane heatsink, the LM4873MTE can continuously drive a 3Ω load to full
power. The LM4873LQ achieves the same output power level without forced air cooling. In all circumstances and
conditions, the junction temperature must be held below 150°C to prevent activating the LM4873's thermal
shutdown protection. The LM4873's power de-rating curve in the TYPICAL PERFORMANCE
CHARACTERISTICS shows the maximum power dissipation versus temperature. Example PCB layouts for the
exposed-DAP TSSOP and LQ packages are shown in the RECOMMENDED PRINTED CIRCUIT BOARD
LAYOUT section. Further detailed and specific information concerning PCB layout, fabrication, and mounting an
LQ (WQFN) package is available from Texas Instruments' AN-1187 (literature number SNOA401).
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PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω
LOADS
Power dissipated by a load is a function of the voltage swing across the load and the load's impedance. As load
impedance decreases, load dissipation becomes increasingly dependent on the interconnect (PCB trace and
wire) resistance between the amplifier output pins and the load's connections. Residual trace resistance causes
a voltage drop, which results in power dissipated in the trace and not in the load as desired. For example, 0.1Ω
trace resistance reduces the output power dissipated by a 4Ω load from 2.1W to 2.0W. This problem of
decreased load dissipation is exacerbated as load impedance decreases. Therefore, to maintain the highest load
dissipation and widest output voltage swing, PCB traces that connect the output pins to a load must be as wide
as possible.
Poor power supply regulation adversely affects maximum output power. A poorly regulated supply's output
voltage decreases with increasing load current. Reduced supply voltage causes decreased headroom, output
signal clipping, and reduced output power. Even with tightly regulated supplies, trace resistance creates the
same effects as poor supply regulation. Therefore, making the power supply traces as wide as possible helps
maintain full output voltage swing.
* Refer to the section SELECTING PROPER EXTERNAL COMPONENTS, for a detailed discussion of CB size.
Pin out shown for the 28-pin Exposed-DAP TSSOP package. Refer to the Connection Diagrams for the pin out of the
20-pin Exposed-DAP TSSOP, Exposed-DAP WQFN, and DSBGA package.
Figure 46. Typical Audio Amplifier Application Circuit
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 46, the LM4873 consists of two pairs of operational amplifiers, forming a two-channel
(channel A and channel B) stereo amplifier. (Though the following discusses channel A, it applies equally to
channel B.) External resistors Rf and Ri set the closed-loop gain of Amp1A, whereas two internal 20kΩ resistors
set Amp2A's gain at −1. The LM4873 drives a load, such as a speaker, connected between the two amplifier
outputs, −OUTA and +OUTA.
Figure 46 shows that Amp1A's output serves as Amp2A'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 −OUTA and +OUTA and driven differentially (commonly referred to as “bridge mode”). This results in a
differential gain of
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AVD = 2 * (Rf/R i)
(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 singleended configuration: its differential output doubles the voltage swing across the load. 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 or that the output signal is not clipped.
To ensure minimum output signal clipping when choosing an amplifier's closed-loop gain, refer to the AUDIO
POWER AMPLIFIER DESIGN section.
Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by
biasing channel A's and channel B's outputs at half-supply. This eliminates the coupling capacitor that single
supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a 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.
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 = (VDD)2/(2π2RL)
Single-Ended
(2)
However, a direct consequence of the increased power delivered to the load by a bridge amplifier is higher
internal power dissipation for the same conditions.
The LM4873 has two operational amplifiers per channel. The maximum internal power dissipation per channel
operating in the bridge mode is four times that of a single-ended amplifier. From Equation 3, assuming a 5V
power supply and a 4Ω load, the maximum single channel power dissipation is 1.27W or 2.54W for stereo
operation.
PDMAX = 4 * (VDD)2/(2π2RL)
Bridge Mode
(3)
The LM4873's power dissipation is twice that given by Equation 2 or Equation 3 when operating in the singleended mode or bridge mode, respectively. Twice 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 LM4873's TJMAX = 150°C. In the LQ package soldered to a DAP pad that expands to a copper area of 5in2
on a PCB, the LM4873's θJA is 20°C/W. In the MTE and MTE-1 packages soldered to a DAP pad that expands to
a copper area of 2in2 on a PCB, the LM4873's θJA is 41°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 LM4873's maximum junction
temperature.
TA = TJMAX – 2*PDMAX θJA
(5)
For a typical application with a 5V power supply and an 4Ω load, the maximum ambient temperature that allows
maximum stereo power dissipation without exceeding the maximum junction temperature is approximately 99°C
for the LQ package and 45°C for the MTE and MTE-1 packages.
TJMAX = PDMAX θJA + TA
(6)
Equation 6 gives the maximum junction temperature TJMAX. If the result violates the LM4873'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 a surface mount part 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.
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If the result of Equation 2 is greater than that of Equation 3, then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. 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 pin(s), supply pin and amplifier output pins. External, solder attached SMT heatsinks such as the
Thermalloy 7106D can also improve power dissipation. When adding a heat sink, the θJA is the sum of θJC, θCS,
and θSA. (θJC is the junction-to-case thermal impedance, θCS is the case-to-sink thermal impedance, and θSA is
the sink-to-ambient thermal impedance.) Refer to the TYPICAL PERFORMANCE CHARACTERISTICS curves
for power dissipation information at lower output power levels.
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 5V regulator typically use a 10 µF in parallel with a 0.1 µF 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 1.0 µF tantalum bypass capacitance connected
between the LM4873'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 LM4873's power
supply pin and ground as short as possible. Connecting a 1µF capacitor, CB, between 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 amplifier's click and pop performance. The selection of bypass capacitor values, especially
CB, depends on desired PSRR requirements, click and pop performance (as explained in the section,
SELECTING PROPER EXTERNAL COMPONENTS), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LM4873's shutdown function. Activate micro-power
shutdown by applying VDD to the SHUTDOWN pin. When active, the LM4873's micro-power shutdown feature
turns off the amplifier's bias circuitry, reducing the supply current. The logic threshold is typically VDD/2. The low
0.7 µA typical shutdown current is achieved by applying a voltage that is as near as VDD as possible to the
SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. Table 2 shows the logic
signal levels that activate and deactivate micro-power shutdown and headphone amplifier operation.
There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw
switch, a microprocessor, or a microcontroller. When using a switch, connect an external 10kΩ pull-up resistor
between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select
normal amplifier operation by closing the switch. Opening the switch connects the SHUTDOWN pin to VDD
through the pull-up resistor, 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 control voltage to the SHUTDOWN pin. Driving the SHUTDOWN
pin with active circuitry eliminates the pull up resistor.
Table 2. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation
SHUTDOWN
PIN
HP-INPIN
MUX CHANNEL
SELECT PIN
OPERATIONAL MODE
(MUX INPUT CHANNEL #)
Logic Low
Logic Low
Logic Low
Logic Low
Bridged Amplifiers (1)
Logic Low
Logic High
Bridged Amplifiers (2)
Logic Low
Logic Low
Logic High
Logic Low
Single-Ended Amplifiers (1)
Logic High
Logic High
Logic High
Single-Ended Amplifiers (2)
X
X
Micro-Power Shutdown
HP-IN FUNCTION
Applying a voltage between 4V and VDD to the LM4873's HP-IN headphone control pin turns off Amp2A and
Amp2B, muting a bridged-connected load. Quiescent current consumption is reduced when the IC is in this
single-ended mode.
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Figure 47 shows the implementation of the LM4873's headphone control function. With no headphones
connected to the headphone jack, the R1-R2 voltage divider sets the voltage applied to the HP-IN pin (pin 16) at
approximately 50mV. This 50mV enables Amp1B and Amp2B, placing the LM4873 in bridged mode operation.
The output coupling capacitor blocks the amplifier's half supply DC voltage, protecting the headphones.
The HP-IN threshold is set at 4V. While the LM4873 operates in bridged mode, the DC potential across the load
is essentially 0V. Therefore, even in an ideal situation, the output swing cannot cause a false single-ended
trigger. Connecting headphones to the headphone jack disconnects the headphone jack contact pin from −OUTA
and allows R1 to pull the HP Sense pin up to VDD. This enables the headphone function, turns off Amp2A and
Amp2B, and mutes the bridged speaker. The amplifier then drives the headphones, whose impedance is in
parallel with resistor R2 and R3. These resistors have negligible effect on the LM4873's output drive capability
since the typical impedance of headphones is 32Ω.
Figure 47 also shows the suggested headphone jack electrical connections. The jack is designed to mate with a
three-wire plug. The plug's tip and ring should each carry one of the two stereo output signals, whereas the
sleeve should carry the ground return. A headphone jack with one control pin contact is sufficient to drive the HPIN pin when connecting headphones.
A microprocessor or a switch can replace the headphone jack contact pin. When a microprocessor or switch
applies a voltage greater than 4V to the HP-IN pin, a bridge-connected speaker is muted and Amp1A and
Amp2A drive a pair of headphones.
Figure 47. Headphone Circuit
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4873's performance requires properly selecting external components. Though the LM4873
operates well when using external components with wide tolerances, best performance is achieved by optimizing
component values.
The LM4873 is unity-gain stable, giving a designer maximum design flexibility. The gain should be set to no more
than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum signal-tonoise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain demands
input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources
such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the AUDIO POWER AMPLIFIER
DESIGN section for more information on selecting the proper gain.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value input coupling capacitor (Ci in Figure 46). A high
value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases,
however, the speakers used in portable systems, whether internal or external, have little ability to reproduce
signals below 150 Hz. Applications using speakers with this limited frequency response reap little improvement
by using large input capacitor.
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Besides effecting system cost and size, Ci has an affect on the LM4873's click and pop performance. When the
supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero
to a quiescent state. The magnitude of the pop is directly proportional to the input capacitor's size. Higher value
capacitors need more time to reach a quiescent DC voltage (usually VDD/2) when charged with a fixed current.
The amplifier's output charges the input capacitor through the feedback resistor, Rf. Thus, pops can be
minimized by selecting an input capacitor value that is no higher than necessary to meet the desired −3dB
frequency.
As shown in Figure 46, the input resistor (RI) and the input capacitor, CI produce a −3dB high pass filter cutoff
frequency that is found using Equation 7.
(7)
As an example when using a speaker with a low frequency limit of 150Hz, Ci, using Equation 4 is 0.063µF. The
1.0µF Ci shown in Figure 46 allows the LM4873 to drive high efficiency, full range speaker whose response
extends below 30Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consideration should be paid to value of CB, the capacitor
connected to the BYPASS pin. Since CB determines how fast the LM4873 settles to quiescent operation, its
value is critical when minimizing turn-on pops. The slower the LM4873's outputs ramp to their quiescent DC
voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 1.0 µF along with a small value of
Ci (in the range of 0.1 µF to 0.39 µF), produces a click-less and pop-less shutdown function. As discussed
above, choosing Ci no larger than necessary for the desired bandwith helps minimize clicks and pops.
OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE
The LM4873 contains circuitry that minimizes turn-on and shutdown transients or “clicks and pop”. For this
discussion, turn-on refers to either applying the power supply voltage or when the shutdown mode is deactivated.
While the power supply is ramping to its final value, the LM4873's internal amplifiers are configured as unity gain
buffers. An internal current source changes the voltage of the BYPASS pin in a controlled, linear 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 on the bypass pin reaches 1/2 VDD . As soon as the voltage on the bypass pin is stable,
the device becomes fully operational. Although the BYPASS pin current cannot be modified, changing the size of
CB alters the device's turn-on time and the magnitude of “clicks and pops”. Increasing the value of CB reduces
the magnitude of turn-on pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time
increases. There is a linear relationship between the size of CB and the turn-on time. Here are some typical turnon times for various values of CB:
CB
TON
0.01µF
20ms
0.1µF
200ms
0.22µF
440ms
0.47µF
940ms
1.0µF
2sec
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”. In a single-ended configuration,
the output is coupled to the load by COUT. This capacitor usually has a high value. COUT discharges through
internal 20kΩ resistors. Depending on the size of COUT, the discharge time constant can be relatively large. To
reduce transients in single-ended mode, an external 1kΩ–5kΩ resistor can be placed in parallel with the internal
20kΩ resistor. The tradeoff for using this resistor is increased quiescent current.
NO LOAD STABILITY
The LM4873 may exhibit low level oscillation when the load resistance is greater than 10kΩ. This oscillation only
occurs as the output signal swings near the supply voltages. Prevent this oscillation by connecting a 5kΩ
between the output pins and ground.
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AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8Ω Load
The following are the desired operational parameters:
Power Output:
1WRMS
Load Impedance:
8Ω
Input Level:
1Vrms
Input Impedance:
20kΩ
Bandwidth:
100Hz−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 Supply Voltage curve in the 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 Dropout Voltage vs Supply Voltage in the TYPICAL
PERFORMANCE CHARACTERISTICS curves, must be added to the result obtained by Equation 8. The result in
Equation 9.
(8)
(9)
VDD ≥ (VOUTPEAK + (VODTOP + VODBOT))
The Output Power vs Supply Voltage graph for an 8Ω load indicates a minimum supply voltage of 4.6V. This is
easily met by the commonly used 5V supply voltage. The additional voltage creates the benefit of headroom,
allowing the LM4873 to produce peak output power in excess of 1W without clipping or other audible distortion.
The choice of supply voltage must also not create a situation that violates maximum power dissipation as
explained above in the POWER DISSIPATION section.
After satisfying the LM4873's power dissipation requirements, the minimum differential gain needed to achieve
1W dissipation in an 8Ω load is found using Equation 10.
(10)
Thus, a minimum gain of 2.83 allows the LM4873's to reach full output swing and maintain low noise and THD+N
performance. For this example, let AVD = 3.
The amplifier's overall gain is set using the input (Ri) and feedback (Rf) resistors. With the desired input
impedance set at 20kΩ, the feedback resistor is found using Equation 11.
Rf/Ri = AVD/2
(11)
The value of Rf is 30kΩ.
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 = 100Hz/5 = 20Hz
and an
fH = 20kHz*5 = 100kHz.
As mentioned in the External Components Description, Ri and Ci create a highpass filter that sets the amplifier's
lower bandpass frequency limit. Find the coupling capacitor's value using Equation 12.
Ci ≥ 1/(2πRifL)
(12)
The result is
1/(2π*20kΩ*20Hz) = 0.398µF.
(13)
Use a 0.39µF capacitor, the closest standard value.
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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 = 3 and fH = 100kHz, the closed-loop gain bandwidth
product (GBWP) is 300kHz. This is less than the LM4873'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 48 through Figure 50 show the recommended two-layer PC board layout that is optimized for the 20-pin
MTE-packaged LM4873 and associated external components. Figure 51 through Figure 55 show the
recommended four-layer PC board layout that is optimized for the 24-pin LQ-packaged LM4873 and associated
external components. Figure 56 through Figure 60 show the recommended four-layer PC board layout that is
optimized for the 20-pin DSBGA-packaged LM4873 and associated external components. These circuits are
designed for use with an external 5V supply and 4Ω speakers.
These circuit boards are easy to use. Apply 5V and ground to the board's VDD and GND pads, respectively.
Connect 4Ω speakers between the board's −OUTA and +OUTA and OUTB and +OUTB pads.
Figure 48. Recommended MTE PC Board Layout:
Component-Side Silkscreen
Figure 49. Recommended MTE PC Board Layout:
Component-Side Layout
Figure 50. Recommended MTE PC Board Layout:
Bottom-Side Layout
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Figure 51. Recommended LQ PC Board Layout:
Component-Side Silkscreen
Figure 52. Recommended LQ PC Board Layout:
Component-Side Layout
Figure 53. Recommended LQ PC Board Layout:
Upper Inner-Layer Layout
Figure 54. Recommended LQ PC Board Layout:
Lower Inner-Layer Layout
Figure 55. Recommended LQ PC Board Layout:
Bottom-Side Layout
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Figure 56. Recommended 20-pin DSBGA
PC Board Layout: Component-Side Silkscreen
Figure 57. Recommended 20-pin DSBGA
PC Board Layout: Component-Side Layout
Figure 58. Recommended 20-pin DSBGA
PC Board Layout: Upper Inner-Layer Layout
Figure 59. Recommended 20-pin DSBGA
PC Board Layout: Lower Inner-Layer Layout
Figure 60. Recommended 20-pin DSBGA
PC Board Layout: Bottom-Side Layout
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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
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM4873MTE/NOPB
ACTIVE
HTSSOP
PWP
20
250
RoHS & Green
SN
Level-1-260C-UNLIM
LM4873MTEX/NOPB
ACTIVE
HTSSOP
PWP
20
2500
RoHS & Green
SN
Level-1-260C-UNLIM
LM4873
MTE
-40 to 85
LM4873
MTE
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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