LM4898 1W Fully Diff Audio Pwr Amp w/Shutdown Select (Rev. E)

LM4898 1W Fully Diff Audio Pwr Amp w/Shutdown Select (Rev. E)
LM4898, LM4898MMBD
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LM4898
1 Watt Fully Differential Audio Power Amplifier
With Shutdown Select
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FEATURES
DESCRIPTION
•
•
The LM4898 is a fully differential audio power
amplifier
primarily
designed
for
demanding
applications in mobile phones and other portable
communication device applications. It is capable of
delivering 1 watt of continuous average power to an
8Ω BTL load with less than 1% distortion (THD+N)
from a 5VDC power supply.
1
2
•
•
•
•
•
•
Fully Differential Amplification
Available in Space-Saving Packages DSBGA,
VSSOP, and WSON
Ultra Low Current Shutdown Mode
Can Drive Capacitive Loads up to 500pF
Improved Pop and Click Circuitry Eliminates
Noises During Turn-On and Turn-Off
Transitions
2.4 - 5.5V Operation
No Output Coupling Capacitors, Snubber
Networks or Bootstrap Capacitors Required
Shutdown High or Low Selectivity
APPLICATIONS
•
•
•
Mobile Phones
PDAs
Portable Electronic Devices
KEY SPECIFICATIONS
•
•
•
•
Improved PSRR at 217Hz: 83 dB(typ)
Power Output at 5.0V, 1% THD: 1.0 W(typ)
Power Output at 3.3V, 1% THD: 400 mW(typ)
Shutdown Current: 0.1µA(typ)
Boomer audio power amplifiers were designed
specifically to provide high quality output power with a
minimal amount of external components. The
LM4898 does not require output coupling capacitors
or bootstrap capacitors, and therefore is ideally suited
for mobile phone and other low voltage applications
where minimal power consumption is a primary
requirement.
The LM4898 features a low-power consumption
shutdown mode. To facilitate this, Shutdown may be
enabled by either logic high or low depending on
mode selection. Driving the shutdown mode pin either
high or low enables the shutdown select pin to be
driven in a likewise manner to enable Shutdown.
Additionally, the LM4898 features an internal thermal
shutdown protection mechanism.
The LM4898 contains advanced pop and click
circuitry which virtually eliminates noises which would
otherwise occur during turn-on and turn-off
transitions.
Connection Diagrams
Top View
Figure 1. VSSOP Package
See Package Number DGS0010A
Top View
Top View
Figure 2. WSON Package
See Package Number NGZ0010B
Figure 3. 9 Bump DSBGA
Package
See Package Number
YZR0009AAA
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.
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Typical Application
Figure 4. Typical Audio Amplifier Application Circuit
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
Thermal Resistance
150°C
θJC (WSON)
12°C/W
θJA (WSON)
63°C/W
θJA (DSBGA)
220°C/W
θJC (VSSOP)
56°C/W
θJA (VSSOP)
190°C/W
For Soldering Information, see AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009).
(1)
(2)
(3)
(4)
(5)
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 = 3V 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.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
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 PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever
is lower.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF–240pF discharged through all pins.
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Operating Ratings
TMIN ≤ TA ≤ TMAX
Temperature Range
−40°C ≤ TA ≤ 85°C
2.4V ≤ VDD ≤ 5.5V
Supply Voltage
Electrical Characteristics VDD = 5V
(1) (2) (3)
The following specifications apply for VDD = 5V, 8Ω load, and AV = 1V/V, unless otherwise specified. Limits apply for TA =
25°C.
Parameter
IDD
Test Conditions
Quiescent Power Supply Current
LM4898
Typ
(4)
Limit (5)
VIN = 0V, no load
3
6
VIN = 0V, RL = 8 Ω
5
10
0.1
1
ISD
Shutdown Current
VSDMODE = VSHUTDOWN = GND
Po
Output Power
THD = 1% (max); f = 1 kHz
LM4898LD, RL= 4Ω (6)
1.4
Units
(Limits)
mA (max)
µA (max)
W (min)
LM4898, RL= 8Ω
1
0.05
%
83
dB (min)
THD+N
Total Harmonic Distortion+Noise
Po = 0.4 Wrms; f = 1kHz
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
f = 217Hz
f = 1kHz
(7)
f = 217Hz
f = 1kHz
(7)
(8)
(8)
0.9
90
83
71
83
71
CMRR
Common_Mode Rejection Ratio
f = 217Hz
VCM = 200mVDD
VOS
Output Offset
VIN = 0V
VSDIH
Shutdown Voltage Input High
SD Mode = GND
VSDIL
Shutdown Voltage Input Low
SD Mode = GND
0.7
V
VSDIH
Shutdown Voltage Input High
SD Mode = VDD
0.9
V
VSDIL
Shutdown Voltage Input Low
SD Mode = VDD
0.7
V
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
50
dB
2
mV
0.9
V
All voltages are measured with respect to the ground pin, unless otherwise specified.
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 = 3V 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.
For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
Typicals are measured at 25°C and represent the parametric norm.
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
When driving 4Ω loads from a 5V supply, the LM4898LD must be mounted to a circuit board with the exposed-DAP area soldered down
to a 1sq. in plane of 1oz. copper.
Unterminated input.
10Ω terminated input.
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Electrical Characteristics VDD = 3V (1)
(2) (3)
The following specifications apply for VDD = 3V, 8Ω load and AV = 1V/V, unless otherwise specified. Limits apply for TA =
25°C.
Parameter
IDD
LM4898
Test Conditions
Quiescent Power Supply Current
Typ (4)
Limit (5)
Units
(Limits)
2.5
5 .5
mA (max)
4
9
1
VIN = 0V, no load
VIN = 0V, RL = 8 Ω
ISD
Shutdown Current
VSDMODE = VSHUTDOWN = GND
0.1
Po
Output Power
THD = 1% (max); f = 1kHz LM4898,
RL = 8Ω
0.35
W
THD+N
Total Harmonic Distortion+Noise
Po = 0.25Wrms; f = 1kHz
0.03
%
PSRR
Power Supply Rejection Ratio
Vripple = 200mV sine p-p
83
dB
f = 217Hz
f = 1kHz
f = 217Hz
f = 1kHz
(6)
(6)
µA (max)
84
(7)
83
(7)
83
CMRR
Common-Mode Rejection Ratio
f = 217Hz
VCM = 200mVPP
50
dB
VOS
Output Offset
VIN = 0V
2
mV
VSDIH
Shutdown Voltage Input High
SD Mode = GND
0.8
V
VSDIL
Shutdown Voltage Input Low
SD Mode = GND
0.6
V
VSDIH
Shutdown Voltage Input High
SD Mode = VDD
0.8
V
VSDIL
Shutdown Voltage Input Low
SD Mode = VDD
0.6
V
(1)
(2)
(3)
(4)
(5)
(6)
(7)
All voltages are measured with respect to the ground pin, unless otherwise specified.
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 = 3V 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.
For DSBGA only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a
maximum of 2µA.
Typicals are measured at 25°C and represent the parametric norm.
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
Unterminated input.
10Ω terminated input.
External Components Description
(See Figure 4)
Components
4
Functional Description
1.
CS
Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for
information concerning proper placement and selection of the supply bypass capacitor.
2.
CB
Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External
Components, for information concerning proper placement and selection of CB.
3.
Ri
Inverting input resistance which sets the closed-loop gain in conjunction with Rf.
4.
Rf
Feedback resistance which sets the closed-loop gain in conjunction with Ri.
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Typical Performance Characteristics
NGZ0010B Specific Characteristics
THD+N vs Output Power
VDD = 5V, RL = 4Ω
THD+N vs Frequency
VDD = 5V, RL = 4Ω, PO = 1W
10
10
20kHz
1
THD+N (%)
THD+N (%)
1
1kHz
0.1
0.1
20Hz
0.01
0.01
0.001
10m
100m
1
3
0.001
20
OUTPUT POWER (W)
100
1k
Figure 5.
Figure 6.
LM4898
Power Dissipation vs Output Power
LM4898
Power Derating Curve
Figure 7.
Figure 8.
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10k 20k
FREQUENCY (Hz)
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Typical Performance Characteristics
Non-NGZ0010B Specific Characteristics
THD+N vs Frequency
VDD = 3V, RL = 8Ω, PO = 275mW
10
10
1
1
THD+N (%)
THD+N (%)
THD+N vs Frequency
VDD = 5V, RL = 8Ω, PO = 400mW
0.1
0.01
0.1
0.01
0.001
20
100
1k
0.001
20
10k 20k
100
Figure 10.
THD+N vs Frequency
VDD = 3V, RL = 4Ω, PO = 225mW
THD+N vs Frequency
VDD = 2.6V, RL = 8Ω, PO = 150mW
10
10
1
1
0.1
0.1
0.01
0.001
20
100
1k
0.001
20
10k 20k
100
FREQUENCY (Hz)
1k
10k 20k
FREQUENCY (Hz)
Figure 11.
Figure 12.
THD+N vs Frequency
VDD = 2.6V, RL = 4Ω, PO = 150mW
THD+N vs Output Power
VDD = 5V, RL = 8Ω
10
10
1
1
THD+N (%)
THD+N (%)
10k 20k
Figure 9.
0.01
0.1
0.01
0.001
20
20kHz
1kHz
0.1
20Hz
0.01
100
1k
10k 20k
0.001
10m
FREQUENCY (Hz)
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100m
1
2
OUTPUT POWER (W)
Figure 13.
6
1k
FREQUENCY (Hz)
THD+N (%)
THD+N (%)
FREQUENCY (Hz)
Figure 14.
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Typical Performance Characteristics
Non-NGZ0010B Specific Characteristics (continued)
THD+N vs Output Power
VDD = 3V, RL = 8Ω
THD+N vs Output Power
VDD = 3V, RL = 4Ω
10
10
20kHz
20kHz
1
THD+N (%)
THD+N (%)
1
1kHz
0.1
1kHz
0.1
20Hz
20Hz
0.01
0.001
10m
0.01
100m
0.001
10m
1
100m
OUTPUT POWER (W)
Figure 15.
Figure 16.
THD+N vs Output Power
VDD = 2.6V, RL = 8Ω
THD+N vs Output Power
VDD = 2.6V, RL = 4Ω
10
10
20kHz
20kHz
1
THD+N (%)
1
THD+N (%)
1
OUTPUT POWER (W)
1kHz
0.1
1kHz
0.1
20Hz
0.01
20Hz
0.001
10m
0.01
100m
0.001
10m
1
100m
1
OUTPUT POWER (W)
Figure 17.
Figure 18.
PSRR vs Frequency
VDD = 5V, RL = 8Ω, Input 10Ω Terminated
PSRR vs Frequency
VDD = 3V, RL = 8Ω, Input 10Ω Terminated
0
0
-10
-10
-20
-20
-30
-30
PSRR (dB)
PSRR (dB)
OUTPUT POWER (W)
-40
-50
-60
-40
-50
-60
-70
-70
-80
-80
-90
-90
-100
20
-100
20
100
1k
10k
100
FREQUENCY (Hz)
100
1k
10k
100
FREQUENCY (Hz)
Figure 19.
Figure 20.
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Typical Performance Characteristics
Non-NGZ0010B Specific Characteristics (continued)
Output Power vs Supply Voltage
RL = 4Ω
2
2
1.8
1.8
1.6
1.6
OUTPUT POWER (W)
OUTPUT POWER (W)
Output Power vs Supply Voltage
RL = 8Ω
1.4
1.2
10% THD+N
1
800m
1% THD+N
600m
1.4
1.2
1
600m
400m
400m
200m
200m
0
2.2 2.5
3
3.5
4
4.5
5
5.5
10% THD+N
800m
1% THD+N
0
2.2
SUPPLY VOLTAGE (V)
8
2.5
3
3.5
4
SUPPLY VOLTAGE (V)
Figure 21.
Figure 22.
Power Dissipation vs Output Power
Power Dissipation vs Output Power
Figure 23.
Figure 24.
Power Dissipation vs Output Power
Output Power vs Load Resistance
Figure 25.
Figure 26.
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Typical Performance Characteristics
Non-NGZ0010B Specific Characteristics (continued)
Supply Current vs Shutdown Voltage
Shutdown Low
Supply Current vs Shutdown Voltage
Shutdown High
Figure 27.
Figure 28.
Clipping (Dropout) Voltage vs Supply Voltage
Open Loop Frequency Response
Figure 29.
Figure 30.
Power Derating Curve
Noise Floor
OUTPUT NOISE VOLTAGE (V)
100u
Vo1 + Vo2
10u
1u
Shutdown On
100n
20
100
1k
10k 20k
FREQUENCY (Hz)
Figure 31.
Figure 32.
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Typical Performance Characteristics
Non-NGZ0010B Specific Characteristics (continued)
CMRR vs Frequency
VDD = 3V, RL = 8Ω, 200mVpp
0
0
-10
-10
-20
-20
-30
-30
CMRR (dB)
CMRR (dB)
CMRR vs Frequency
VDD = 5V, RL = 8Ω, 200mVpp
-40
-50
-60
-40
-50
-60
-70
-70
-80
-80
-90
-90
-100
20
100
1k
10k
-100
20
100
100
Figure 34.
PSRR vs Common Mode Voltage
VDD = 5V
PSRR vs Common Mode Voltage
VDD = 3V, RL = 8Ω, 217Hz, 200mVpp
0
0
-10
-20
-20
-30
-30
-40
-50
-60
-40
-50
-60
-70
-70
-80
-80
-90
-90
-100
-100
1
2
3
4
DC COMMON-MODE VOLTAGE (V)
5
0
0.6
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1.2
1.8
2.4
3
DC COMMON-MODE VOLTAGE (V)
Figure 35.
10
100
FREQUENCY (Hz)
-10
0
10k
Figure 33.
PSRR (dB)
PSRR (dB)
FREQUENCY (Hz)
1k
Figure 36.
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APPLICATION INFORMATION
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4898 is a fully differential audio amplifier that features differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a common mode feedback amplifier that adjusts the
output voltages so that the average value remains VDD/2. When setting the differential gain, the amplifier can be
considered to have two "halves". Each half uses an input and feedback resistor (Ri1 and Rf1) to set its respective
closed-loop gain (see Figure 4). With Ri1 = Ri2 and Rf1 = Rf2, the gain is set at -Rf/Ri for each half. This results
in a differential gain of
AVD = -Rf/Ri
(1)
It is extremely important to match the input resistors to each other, as well as the feedback resistors to each
other for best amplifier performance. See the PROPER SELECTION OF EXTERNAL COMPONENTS section for
more information. A differential amplifier works in a manner where the difference between the two input signals is
amplified. In most applications, this would require input signals that are 180° out of phase with each other. The
LM4898 can be used, however, as a single ended input amplifier while still retaining its fully differential benefits.
In fact, completely unrelated signals may be placed on the input pins. The LM4898 simply amplifies the
difference between them.
All of these applications, either single-ended or fully differential, provide what is known as a "bridged mode"
output (bridge-tied-load, BTL). This results in output signals at Vo1 and Vo2 that are 180° out of phase with
respect to each other. Bridged mode operation is different from the single-ended amplifier configuration that
connects the load between the amplifier output and ground. A bridged amplifier design has distinct advantages
over the single-ended configuration: it provides differential drive to the load, thus doubling maximum possible
output swing for a specific supply voltage. Four times the output power is possible compared with a single-ended
amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not
current limited or clipped. In order to choose an amplifier’s closed-loop gain without causing excess clipping,
please refer to the AUDIO POWER AMPLIFIER DESIGN.
A bridged configuration, such as the one used in the LM4898, also creates a second advantage over singleended amplifiers. Since the differential outputs, Vo1 and Vo2,are biased at half-supply, no net DC voltage exists
across the load. This assumes that the input resistor pair and the feedback resistor pair are properly matched
(see PROPER SELECTION OF EXTERNAL COMPONENTS). BTL configuration eliminates the output coupling
capacitor required in single supply, single-ended amplifier configurations. If an output coupling capacitor is not
used in a single-ended output configuration, the half-supply bias across the load would result in both increased
internal IC power dissipation as well as permanent loudspeaker damage. Further advantages of bridged mode
operation specific to fully differential amplifiers like the LM4898 include increased power supply rejection ratio,
common-mode noise reduction, and click and pop reduction.
EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS
The LM4898’s exposed-DAP (die attach paddle) package (NGZ0010B) provides 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 1.4W 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
LM4898’s high power performance and activate unwanted, though necessary, thermal shutdown protection. The
NGZ0010B package must have its DAP 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 4 (2x2) vias. The via diameter should be 0.012in - 0.013in with a 0.050in pitch. Ensure
efficient thermal conductivity by plating through and solder-filling the vias.
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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 LM4898 should be 5in2 (min) for the same supply
voltage and load resistance. The last two area recommendations apply for 25°C ambient temperature. In all
circumstances and conditions, the junction temperature must be held below 150°C to prevent activating the
LM4898’s thermal shutdown protection. The LM4898’s power derating curve in the TYPICAL PERFORMANCE
CHARACTERISTICS shows the maximum power dissipation versus temperature. Further detailed and specific
information concerning PCB layout, fabrication, and mounting an WSON package is available from Texas
Instruments package Engineering Group under application note AN-1187 (SNOA401).
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 1.4W to1.37W. 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.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or
single-ended. 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 an increase
in internal power dissipation versus a single-ended amplifier operating at the same conditions.
PDMAX = 4*(VDD)2/(2π2RL) Bridge Mode
(3)
Since the LM4898 has bridged outputs, the maximum internal power dissipation is 4 times that of a single-ended
amplifier. Even with this substantial increase in power dissipation, the LM4898 does not require additional
heatsinking under most operating conditions and output loading. From Equation 3, assuming a 5V power supply
and an 8. load,the maximum power dissipation point is 625mW. The maximum power dissipation point obtained
from Equation 3 must not be greater than the power dissipation results from Equation 4:
PDMAX = (TJMAX - TA)/θJA
(4)
The LM4898’s θJA in an DGS0010A package is 190°C/W. Depending on the ambient temperature, TA, of the
system surroundings, Equation 4 can be used to find the maximum internal power dissipation supported by the
IC packaging. If the result of Equation 3 is greater than that of Equation 4, then either the supply voltage must be
decreased, the load impedance increased, the ambient temperature reduced, or theθJA reduced with heatsinking.
In many cases, larger traces near the output, VDD, and GND pins can be used to lower the θJA. The larger areas
of copper provide a form of heatsinking allowing higher power dissipation. For the typical application of a 5V
power supply, with an 8Ω load, the maximum ambient temperature possible without violating the maximum
junction temperature is approximately 30°C provided that device operation is around the maximum power
dissipation point. Recall that internal power dissipation is a function of output power. If typical operation is not
around the maximum power dissipation point, the LM4898 can operate at higher ambient temperatures. Refer to
the TYPICAL PERFORMANCE CHARACTERISTICS curves for power dissipation information.
12
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POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor location on both the bypass and power supply pins should be as close to
the device as possible. A larger half-supply bypass capacitor improves PSRR because it increases half-supply
stability. Typical applications employ a 5V regulator with 10µF and0.1µF bypass capacitors that increase supply
stability. This, however, does not eliminate the need for bypassing the supply nodes of the LM4898. Although the
LM4898 will operate without the bypass capacitor CB, the PSRR may decrease. A 1µF capacitor is
recommended for CB. This value maximizes PSRR performance. Lesser values may be used, but PSRR
decreases at frequencies below 1kHz. The issue of CB selection is thus dependant upon desired PSRR and click
and pop performance as explained in the PROPER SELECTION OF EXTERNAL COMPONENTS.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the LM4898 contains shutdown circuitry that is used to
turn off the amplifier’s bias circuitry. In addition, the LM4898 contains a Shutdown Mode pin, allowing the
designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level
logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply
be tied permanently to either VDD or GND to set the LM4898 as either a "shutdown-high" device or a "shutdownlow" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown Select
pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the
LM4898 enters shutdown mode whenever the two pins are in the same logic state. The trigger point for either
shutdown high or shutdown low is shown as a typical value in the Supply Current vs. Shutdown Voltage graphs
in the TYPICAL PERFORMANCE CHARACTERISTICS section. It is best to switch between ground and supply
for maximum performance. While the device may be disabled with shutdown voltages in between ground and
supply, the idle current maybe greater than the typical value of 0.1µA. In either case, the shutdown pin should be
tied to a definite voltage to avoid unwanted state changes.
In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which
provides a quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction
with an external pull-up resistor (or pull-down, depending on shutdown high or low application). This scheme
ensures that the shutdown pin will not float, thus preventing unwanted state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using integrated power amplifiers is critical when
optimizing device and system performance. Although the LM4898 is tolerant to a variety of external component
combinations, consideration of component values must be made when maximizing overall system quality.
The LM4898 is unity-gain stable, giving the designer maximum system flexibility. The LM4898 should be used in
low closed-loop gain configurations to minimize THD+N values and maximize signal to noise ratio. Low gain
configurations require large input signals to obtain a given output power. Input signals equal to or greater than
1Vrms are available from sources such as audio codecs. Please refer to the AUDIO POWER AMPLIFIER
DESIGN section for a more complete explanation of proper gain selection. When used in its typical application as
a fully differential power amplifier the LM4898 does not require input coupling capacitors for input sources with
DC common-mode voltages of less than VDD. Exact allowable input common-mode voltage levels are actually a
function of VDD, Ri, and Rf and may be determined by Equation 5:
VCMi<(VDD-1.2)*((Rf+(Ri)/(Rf)-VDD*(Ri/2Rf)
Rf/Ri=AVD
(5)
(6)
Special care must be taken to match the values of the feedback resistors (Rf1 and Rf2) to each other as well as
matching the input resistors (Ri1 and Ri2) to each other (see Figure 4). Because of the balanced nature of
differential amplifiers, resistor matching differences can result in net DC currents across the load. This DC
current can increase power consumption, internal IC power dissipation, reduce PSRR, and possibly damaging
the loudspeaker. The chart below demonstrates this problem by showing the effects of differing values between
the feedback resistors while assuming that the input resistors are perfectly matched. The results below apply to
the application circuit shown in Figure 4, and assumes that VDD = 5V, RL = 8Ω, and the system has DC coupled
inputs tied to ground.
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LM4898, LM4898MMBD
SNAS216E – MAY 2003 – REVISED APRIL 2013
Tolerance
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Rf1
Rf2
Vo2-Vo1
ILOAD
20%
0.8R
1.2R
-0.5V
62.5mA
10%
0.9R
1.1R
-0.250V
31.25mA
5%
0.95R
1.05R
-0.125V
15.63mA
1%
0.99R
1.01R
-0.025V
3.125mA
0
R
R
R
0
Similar results would occur if the input resistors were not carefully matched. Adding input coupling capacitors in
between the signal source and the input resistors will eliminate this problem, however, to achieve best
performance with minimum component count it is highly recommended that both the feedback and input resistors
matched to 1% tolerance or better.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8Ω Audio Amplifier
Given:
• Power Output 1W
• Load Impedance 8Ω
• Input Level 1Vrms
• Input Impedance 20kΩ
• Bandwidth 100Hz–20kHz ± 0.25dB
A designer must first determine the minimum supply rail to obtain the specified output power. The supply rail can
easily be found by extrapolating from the Output Power vs. Supply Voltage graphs in the Typical Performance
Characteristics section. A second way to determine the minimum supply rail is to calculate the required Vopeak
using Equation 7 and add the dropout voltages. Using this method, the minimum supply voltage is (Vopeak +(VDO
TOP+(VDO BOT )),where VDO BOT and VDO TOP are extrapolated from the Dropout Voltage vs. Supply Voltage curve
in the Typical Performance Characteristics section.
(7)
Using the Output Power vs. Supply Voltage graph for an 8Ω load, the minimum supply rail just about 5V. Extra
supply voltage creates headroom that allows the LM4898 to reproduce peaks in excess of 1W without producing
audible distortion. At this time, the designer must make sure that the power supply choice along with the output
impedance does not violate the conditions explained in the Power Dissipation section. Once the power
dissipation equations have been addressed, the required differential gain can be determined from Equation 8.
(8)
Rf / Ri = AVD
From Equation 8, the minimum AVD is 2.83. Since the desired input impedance was 20kΩ, a ratio of 2.83:1 of Rf
to Ri results in an allocation of Ri = 20kΩ for both input resistors and Rf= 60kΩ for both feedback resistors. The
final design step is to address the bandwidth requirement which must be stated as a single -3dB frequency point.
Five times away from a -3dB point is 0.17dB down from passband response which is better than the required
±0.25dB specified.
fH = 20kHz * 5 =100kHz
The high frequency pole is determined by the product of the desired frequency pole, fH , and the differential gain,
AVD .With a AVD = 2.83 and fH = 100kHz, the resulting GBWP = 150kHz which is much smaller than the LM4898
GBWP of 10MHz. This figure displays that if a designer has a need to design an amplifier with a higher
differential gain, the LM4898 can still be used without running into bandwidth limitations.
14
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SNAS216E – MAY 2003 – REVISED APRIL 2013
REVISION HISTORY
Changes from Revision D (April 2013) to Revision E
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 14
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15
PACKAGE OPTION ADDENDUM
www.ti.com
26-Aug-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
LM4898LD/NOPB
ACTIVE
WSON
NGZ
10
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-3-260C-168 HR
-40 to 85
L4898
LM4898MM/NOPB
ACTIVE
VSSOP
DGS
10
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
-40 to 85
GB3
(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)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device 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 Device 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.
Addendum-Page 1
Samples
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Aug-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM4898LD/NOPB
WSON
NGZ
10
1000
178.0
12.4
4.3
3.3
1.0
8.0
12.0
Q1
LM4898MM/NOPB
VSSOP
DGS
10
1000
178.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
12-Aug-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM4898LD/NOPB
WSON
NGZ
10
1000
213.0
191.0
55.0
LM4898MM/NOPB
VSSOP
DGS
10
1000
210.0
185.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
NGZ0010B
LDA10B (Rev B)
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