LM4980
2 Cell Battery, 1mA, 42mW Per Channel High Fidelity
Stereo Headphone Audio Amplifier for MP3 players
General Description
Key Specifications
The LM4980 is a stereo headphone audio amplifier, which
when connected to a 3.0V supply, delivers 42mW to a 16Ω
load with less than 1% THD+N. With the LM4980 packaged
in the SD package, the customer benefits include low profile
and small size. This package minimizes PCB area and maximizes output power.
The LM4980 features circuitry that significantly reduces output transients (“clicks” and “pops”) while driving headphones
during device turn-on and turn-off without costly external
additional circuitry. The LM4980 also includes an externally
controlled low-power consumption active-low shutdown
mode, and thermal shutdown. Boomer audio power amplifiers are designed specifically to use few external components and provide high quality output power in a surface
mount package.
j Output power
(RL = 16Ω, VDD = 3.0V, THD+N = 1%)
42mW (typ)
j Quiescent current (VDD = 3V)
1mA (typ)
j Micropower shutdown current
0.1µA (typ)
j Supply voltage operating range
j PSRR @ 1kHz, VDD = 3.0V
j PSRR @ 217Hz, VDD = 3.0V
1.5V < VDD < 3.3V
90dB (typ)
100dB (typ)
Features
n 2-cell 1.5V to 3.3V battery operation
n Unity-gain stable
n “Click and pop” suppression circuitry for shutdown and
power on/off transient with headphone loads
n Active low micro-power shutdown
n Thermal shutdown protection circuitry
Applications
n Portable two-cell audio products
n Portable two-cell electronic devices
n Portable MP3 player/recorders
Typical Application
20142901
FIGURE 1. Block Diagram
Boomer ® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation
DS201429
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LM4980 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier
for MP3 players
July 2005
LM4980
Connection Diagram
SD Package
20142902
Top View
Order Number LM4980SD
See NS Package Number SDA10A
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2
LM4980
Typical Connection
20142903
FIGURE 2. Typical Application Circuit
3
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LM4980
Absolute Maximum Ratings (Note 1)
Infrared (15 sec)
See AN-450 “Surface Mounting and their Effects on
Product Reliablilty” for other methods of soldering
surface mount devices.
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
3.6V
Thermal Resistance
−65˚C to +150˚C
θJA (typ) SDA10A
Supply Voltage
Storage Temperature
220˚C
73˚C/W
−0.3V to VDD +0.3V
Input Voltage
Power Dissipation (Note 2)
Internally limited
ESD Susceptibility(Note 3)
2000V
ESD Susceptibility (Note 4)
200V
Junction Temperature
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
150˚C
Solder Information
Small Outline Package Vapor Phase (60sec)
−40˚C ≤ TA ≤ +85˚C
1.5V ≤ VDD ≤ 3.3V
Supply Voltage
215˚C
Electrical Characteristics VDD = 3.0V (Notes 1, 5)
The following specifications apply for the circuit shown in Figure 2, unless otherwise specified. AV = 0dB, RL = 32Ω.
Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
LM4980
Typical
Limit
Units
(Limits)
(Note 6)
(Note 7)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A, RL = ∞ (Note 8)
1.0
1.5
mA (max)
ISD
Shutdown Current
VSHDN = GND
0.1
1
µA (max)
VOS
Output Offset Voltage
PO
Output Power (Note 9)
1
5
mV
RL = 16Ω,
THD+N = 1%, f = 1kHz, per channel
42
35
mW (min)
RL = 32Ω,
THD+N = 1%, f = 1kHz, per channel
28
mW (min)
µVRMS
VNO
Output Voltage Noise
20Hz to 20kHz, A-weighted, Fig. 2
10
THD+N
Total Harmonic Distortion + Noise
RL = 32Ω, POUT = 10mW, f = 1kHz
Crosstalk
PSRR
Power Supply Rejection Ratio
0.02
%
Freq = 1kHz, POUT = 28mW, RL = 32Ω
77
dB
VRIPPLE = 200mVP-P sine wave
fRIPPLE = 1kHz, CMIDCAP = 4.7µF,
VMID Voltage is Ripple-Free
90
dB
VRIPPLE = 200mVP-P sine wave
fRIPPLE = 217Hz, CMIDCAP = 4.7µF,
VMID Voltage is Ripple-Free
100
dB
dB
CMRR
Common-Mode Rejection Ratio
Input coupling capacitors with 5%
tolerance, VIN = VMID,
fRIPPLE = 1kHz
47
TWAKE-UP
Wake-up Time
CMIDCAP = 4.7µF, Fig 2.
250
VIH
Control Logic High
1.5V ≤ VDD ≤ 3.3V
1.4V
V (min)
VIL
Control Logic Low
1.5V ≤ VDD ≤ 3.3V
0.4V
V (max)
ms
Electrical Characteristics VDD = 1.8V (Notes 1, 5)
The following specifications apply for the circuit shown in Figure 2, unless otherwise specified. AV = 0dB, RL = 32Ω.
Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
LM4980
Typical
Limit
(Note 6)
(Note 7)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A, RL = ∞ (Note 8)
0.9
mA
ISD
Shutdown Current
VSHDN = GND
0.1
µA
VOS
Output Offset Voltage
1
mV
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4
(Continued)
The following specifications apply for the circuit shown in Figure 2, unless otherwise specified. AV = 0dB, RL = 32Ω.
Limits apply for TA = 25˚C.
Symbol
PO
Parameter
Output Power (Note 9)
Conditions
LM4980
Typical
Limit
(Note 6)
(Note 7)
Units
(Limits)
RL = 16Ω,
THD+N = 1%, f = 1kHz, per channel
11
mW (min)
RL = 32Ω,
THD+N = 1%, f = 1kHz, per channel
9
mW (min)
µVRMS
VNO
Output Voltage Noise
20Hz to 20kHz, A-weighted, Fig. 2
9
THD+N
Total Harmonic Distortion + Noise
RL = 32Ω, POUT = 10mW, f = 1kHz
0.03
%
Freq = 1kHz, POUT = 9mW, RL = 32Ω
79
dB
VRIPPLE = 200mVP-P sine wave
fRIPPLE = 1kHz, CMIDCAP = 4.7µF,
VMID Voltage is Ripple-Free
78
dB
VRIPPLE = 200mVP-P sine wave
fRIPPLE = 217Hz, CMIDCAP = 4.7µF,
VMID Voltage is Ripple-Free
85
dB
Crosstalk
PSRR
Power Supply Rejection Ratio
CMRR
Common-Mode Rejection Ratio
Input coupling capacitors with 5%
tolerance, VIN = VMID,
fRIPPLE = 1kHz
47
dB
TWAKE-UP
Wake-up Time
CMIDCAP = 4.7µF, Fig 2.
320
ms
VIH
Control Logic High
1.5V ≤ VDD ≤ 3.3V
1.4V
V (min)
VIL
Control Logic Low
1.5V ≤ VDD ≤ 3.3V
0.4V
V (max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 2: The maximum power dissipation is dictated by TJMAX, θJA, and the ambient temperature TA must be derated at elevated temperatures. The maximum
allowable power dissipation is PDMAX = (TJMAX − TA) / θJA. For the LM4980, TJMAX = 150˚C. For the θJAs, please see the Application Information section or the
Absolute Maximum Ratings section.
Note 3: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 4: Machine model, 200pF – 220pF discharged through all pins.
Note 5: All voltages are measured with respect to the ground (GND) pins unless otherwise specified.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 8: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier.
Note 9: Output power is measured at the device terminals.
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LM4980
Electrical Characteristics VDD = 1.8V (Notes 1, 5)
LM4980
Typical Performance Characteristics (TA = 25˚C)
THD+N vs Frequency
VDD = 2.4V, RL = 32Ω, POUT = 14mW
THD+N vs Frequency
VDD = 1.8V, RL = 32Ω, PO = 7.3mW
20142905
20142913
THD+N vs Frequency
VDD = 1.8V, RL = 16Ω, POUT = 9.3mW
THD+N vs Frequency
VDD = 3V, RL = 32Ω, POUT = 23mW
20142918
20142922
THD+N vs Frequency
VDD = 3V, RL = 16Ω, POUT = 27mW
THD+N vs Frequency
VDD = 2.4V, RL = 16Ω, POUT = 20mW
20142927
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20142928
6
THD+N vs Output Power
VDD = 1.8V, RL = 32Ω
LM4980
Typical Performance Characteristics (TA = 25˚C)
(Continued)
THD+N vs Output Power
VDD = 2.4V, RL = 32Ω
20142935
20142936
THD+N vs Output Power
VDD = 1.8V, RL = 16Ω
THD+N vs Output Power
VDD = 3V, RL = 32Ω
20142938
20142937
THD+N vs Output Power
VDD = 3V, RL = 16Ω
THD+N vs Output Power
VDD = 2.4V, RL = 16Ω
20142939
20142940
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LM4980
Typical Performance Characteristics (TA = 25˚C)
PSRR vs Frequency
VDD = 1.8V, RL = 32Ω, 4.7µ
(Continued)
PSRR vs Frequency
VDD = 2.4V, RL = 32Ω, 4.7µ
20142941
20142942
PSRR vs Frequency
VDD = 1.8V, RL = 32Ω, 1µ
PSRR vs Frequency
VDD = 3V, RL = 32Ω, 4.7µ
20142943
20142944
PSRR vs Frequency
VDD = 3V, RL = 32Ω, 1µ
PSRR vs Frequency
VDD = 2.4V, RL = 32Ω, 1µ
20142945
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20142946
8
Crosstalk vs Frequency
VDD = 1.8V, RL = 32Ω, POUT = 9mW
Channel A Driven, Channel B Measured
(Continued)
Crosstalk vs Frequency
VDD = 1.8V, RL = 32Ω,POUT = 9mW
Channel B Driven, Channel A Measured
20142947
20142948
Crosstalk vs Frequency
VDD = 2.4V, RL = 32Ω, POUT = 17mW
Channel B Driven, Channel A Measured
Crosstalk vs Frequency
VDD = 2.4V, RL = 32Ω, POUT = 17mW
Channel A Driven, Channel B Measured
20142950
20142949
Crosstalk vs Frequency
VDD = 3V, RL = 32Ω, POUT = 27mW
Channel B Driven, Channel A Measured
Crosstalk vs Frequency
VDD = 3V, RL = 32Ω, POUT = 27mW
Channel A Driven, Channel B Measured
20142951
20142953
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LM4980
Typical Performance Characteristics (TA = 25˚C)
LM4980
Typical Performance Characteristics (TA = 25˚C)
Crosstalk vs Frequency
VDD = 1.8V, RL = 16Ω, POUT = 11mW
Channel A Driven, Channel B Measured
Crosstalk vs Frequency
VDD = 1.8V, RL = 16Ω, POUT = 11mW
Channel B Driven, Channel A Measured
20142954
20142956
Crosstalk vs Frequency
VDD = 2.4V, RL = 16Ω, POUT = 24mW
Channel B Driven, Channel A Measured
Crosstalk vs Frequency
VDD = 2.4V, RL = 16Ω, POUT = 24mW
Channel A Driven, Channel B Measured
20142960
20142968
Crosstalk vs Frequency
VDD = 3V, RL = 16Ω, POUT = 42mW
Channel B Driven, Channel A Measured
Crosstalk vs Frequency
VDD = 3V, RL = 16Ω, POUT = 42mW
Channel A Driven, Channel B Measured
20142969
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(Continued)
20142970
10
Output Power vs Supply Voltage
RL = 32Ω
LM4980
Typical Performance Characteristics (TA = 25˚C)
(Continued)
Output Power vs Supply Voltage
RL = 16Ω
20142990
20142991
Output Power vs Load Resistance
VDD = 2.4V
Output Power vs Load Resistance
VDD = 1.8V
20142973
20142974
Load Dissipation vs Amplifier Dissipation
VDD = 1.8V
Output Power vs Load Resistance
VDD = 3.0V
20142975
20142976
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LM4980
Typical Performance Characteristics (TA = 25˚C)
Amplifier Dissipation vs Load Dissipation
VDD = 2.4V
(Continued)
Amplifier Dissipation vs Load Dissipation
VDD = 3.0V
20142978
20142977
Power Supply Current vs Power Supply Voltage
VIN = 0V
20142979
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12
AMPLIFIER CONFIGURATION
As shown in Figure 1, the LM4980 consists of a stereo pair
of audio amplifiers. These amplifiers operate on a single
supply and have single-ended inputs and outputs. The quiescent operating point of each amplifier input and output is
equal to the voltage applied to the VMID pin (usually VDD/2).
TABLE 1. Typical turn-on time versus CMIDCAP value
CMIDCAP VALUE SELECTION
Careful consideration should be paid to value of CMIDCAP,
the capacitor connected between the MIDCAP pin and
ground. The value of CMIDCAP determines how fast the
LM4980 settles to quiescent operation and determines the
amount of output transient suppression. Choosing CMIDCAP
equal to 4.7µF along with a small value of CIN (in the range
of 0.1µF to 1.0µF), produces shutdown function that is essentially output-transient free. Choosing CIN no larger than
necessary for the desired bandwidth helps minimize clicks
and pops. This ensures that output transients are minimized
when power is first applied or the LM4980 resumes operation after shutdown. The MIDCAP offers the following benefits: better linearity for reduced THD+N, reduced channelto-channel crosstalk, and less susceptibility to ground noise.
For the ultimate suppression of output transient when power
is applied or removed, ensure that the voltage applied to the
SHDN pin is a logic low. This will activate the micro-power
shutdown.
CMIDCAP VALUE (µF)
Turn-On Time (ms)
4.7
250
6.8
360
10.0
530
STAND-ALONE VMID VOLTAGE GENERATION
The LM4980 is designed to take advantage of audio DACs
(digital-to-analog converters) and other signal sources that,
in addition to generating an analog signal, also create an AC
ground potential. This AC ground potential is typically VDD/2.
This VDD/2 is applied to the LM4980’s VMID pin (pin 4).
Using two external resistors allows the LM4980 to be easily
used in applications where the VMID voltage is not internally
generated and supplied to the LM4980 by other circuits.
Figure 4 shows this configuration.
OPTIMIZING OUTPUT-GROUND NOISE REDUCTION
In addition to the output-ground noise reduction afforded by
CMIDCAP, further reduction can be achieved by the inclusion
of a ferrite bead. The ferrite bead (FB) is placed between
ground and common connection between the CMIDCAP and
the headphone ground connection. This is shown in Figure
3. The ferrite bead is beneficial in environments where the
headphone and CMIDCAP ground connection is shared with
circuitry (such as video) that may inject noise on a common
ground.
20142980
FIGURE 4. Simple circuit generates LM4980’s VMID
voltage
SELECTING THE OUTPUT COUPLING CAPACITOR
VALUE
To ensure that no performance degrading DC current flows
through the load (something with which speakers would just
as soon not have to tolerate), coupling capacitors are necessary between the amplifier output pins and the load. Besides blocking DC current, the output coupling capacitor
value, together with the load resistance, produces a low
frequency amplitude rolloff, whose cutoff frequency is found
using Equation 1.
20142981
FIGURE 3. Adding a ferrite bead improves
ground-noise suppression
OPTIMIZING OUTPUT TRANSIENT SUPPRESSION
The LM4980 contains circuitry that eliminates turn-on and
shutdown output 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. The turn-on time delay is the time duration that occurs
between the application of the power supply voltage or deactivating shutdown and when the applied input signal appears at the amplifier outputs.
CMIDCAP’s value plays a significant role in the suppression of
output transients. The amount of suppression increases as
(1)
When driving 32Ω headphones, the 220µF CCOUPLING capacitors shown in Figure 2 produce a cutoff frequency equal
to 23Hz.
The output coupling capacitors also influence the output
transient behavior at power-up and when activating or deac13
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LM4980
CMIDCAP’s value increases. However, changing the value of
CMIDCAP alters the LM4980’s turn-on time. There is a linear
relationship between the value of CMIDCAP and the turn-on
time. Here are some typical turn-on times for various values
of CMIDCAP.
Application Information
LM4980
Application Information
MICRO POWER SHUTDOWN
The voltage applied to the shutdown (SHDN) pin controls the
LM4980’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHDN pin. When
active, the LM4980’s micro-power shutdown feature turns off
the amplifier’s bias circuitry, reducing the supply current. The
trigger point is 0.4V (max) for a logic-low level, and 1.4V
(min) for a logic-high level. The low 0.1µA (typ) shutdown
current is achieved by applying a voltage that is as near as
ground as possible to the SHDN pin. A voltage that is higher
than ground may increase the shutdown current.
(Continued)
tivating shutdown. As CCOUPLING’s value increases, output
transient magnitude can also increase. This increase can be
mitigated by a corresponding increase in CMIDCAP’s value. A
minimum starting point when selecting CMIDCAP’s value is
6.8µF when using 220µF output coupling capacitors.
SELECTING THE INPUT CAPACITOR VALUE
Amplifiying the lowest audio frequencies requires a relatively
high value input coupling capacitor, (CIN in Figure 2). A high
value capacitor can be expensive and may compromise
space efficiency in portable designs. In many cases, however, the headphones used in portable systems have limited
ability to reproduce signals below 60Hz. Applications using
headphones with this limited frequency response reap little
improvement by using a high value input capacitor. A small
value of Ci (in the range of 0.1µF to 1.0µF), is recommended.
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 100kΩ pull-up resistor between the
SHDN pin and GND. Connect the switch between the SHDN
pin and VDD. Select normal amplifier operation by closing the
switch. Opening the switch connects the SHDN pin to
ground, activating micro-power shutdown. The switch and
resistor guarantee that the SHDN pin will not float. This
prevents unwanted state changes. In a system with a microprocessor or microcontroller, use a digital output to apply the
control voltage to the SHDN pin. Driving the SHDN pin with
active circuitry eliminates the pull-up resistor.
DRIVING POWERED SPEAKERS
Though the LM4980 is design primarily to drive headphones,
in many cases, it may be called on to act as a line level driver
when powered speakers or other devices may be connected
to the amplifier outputs. For powered speakers or other
devices with typical input resistances (10kΩ) that are significantly higher than the typical headphone resistance (32Ω),
the output transients may not sufficiently suppressed when
using the Figure 2 circuit. If this is anticipated, a minor
modification of an additional resistor (a nominal value of
1kΩ) between each output and ground in the Figure 2 circuit
is needed to ensure that the output transient suppression is
not compromised. This reduces both the load resistance
seen by the LM4980 and the magnitude of power-on and
shutdown output transients.
SUGGESTED PCB SCHEMATIC
Figure 5 is the schematic for the suggested PCB Layout.
This schematic and its associated PCB provide both a lean
tested layout and platform that can be used to verify the
LM4980’s outstanding audio performance.
Suggested PCB Design and Layout
Figures 6 through 9 show a suggested PCB layout for a
headphone amplifier circuit using the LM4980 .
POWER DISSIPATION
Power dissipation has to be evaluated and considered when
designing a successful amplifier. A direct consequence of the
power delivered to a load an amplifier is internal power
dissipation. The maximum per-amplifier power dissipation
for a given application can be derived from the power dissipation graphs or from Equation 2.
PDMAX = VDD2 / 2πRLOAD
PCB Layout Guidelines
This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
ground traces. Designers should note that these are only
"rule-of-thumb" recommendations and the actual results will
depend heavily on the final layout.
(2)
MINIMIZING THD+N
PCB trace impedance on the power, ground, and all output
traces should be minimized to achieve optimal THD performance. Therefore, use PCB traces that are as wide as
possible for these connections. As the gain of the amplifier is
increased, the trace impedance will have an ever increasing
adverse affect on THD performance. At unity-gain (0dB) the
parasitic trace impedance effect on THD performance is
reduced but still a negative factor in the THD performance of
the LM4980 in a given application.
It is critical that the maximum junction temperature TJMAX of
150˚C is not exceeded. Since the typical application is for
headphone operation (16Ω impedance) using a 3.0V supply
the maximum power dissipation is less than 29mW. Therefore, in the case of this headphone amplifier, the power
dissipation is not a major concern.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is important
for low noise performance and high power supply rejection.
The capacitor location on the power supply pins should be
as close to the device as possible. Typical applications employ a 3.0V regulator with 10µF tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply
stability. This does not eliminate the need for local power
supply bypassing connected as close as possible to the
LM4980’s supply pin. A power supply bypass capacitor value
in the range of 1.0µF to 10µF is recommended.
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GENERAL MIXED SIGNAL LAYOUT
RECOMMENDATION
Power and Ground Circuits
For two layer mixed signal design, it is important to isolate
the digital power and ground trace paths from the analog
power and ground trace paths. Star trace routing techniques
(bringing individual traces back to a central point rather than
daisy chaining traces together in a serial manner) can
greatly enhance low level signal performance. Star trace
14
Placement of Digital and Analog Components
(Continued)
All digital components and high-speed digital signal traces
should be located as far away as possible from analog
components and circuit traces.
routing refers to using individual traces to feed power and
ground to each circuit or even device. This technique will
require a greater amount of design time but will not increase
the final price of the board. The only extra parts required may
be some jumpers.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces
parallel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other do it at 90 degrees.
Running digital and analog traces at 90 degrees to each
other from the top to the bottom side as much as possible will
minimize capacitive noise coupling and cross talk.
Single-Point Power and Ground Connections
The analog power traces should be connected to the digital
traces through a single point (link). A "PI-filter" can be helpful
in minimizing high frequency noise coupling between the
analog and digital sections. Further, place digital and analog
power traces over the corresponding digital and analog
ground traces to minimize noise coupling.
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LM4980
Application Information
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16
Schematic for the LM4980 Suggested PCB Layout
FIGURE 5.
20142986
LM4980
LM4980
Suggested PCB Layout
20142982
FIGURE 6. Top Layer
20142983
FIGURE 7. Bottom Layer
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LM4980
Suggested PCB Layout
(Continued)
20142984
FIGURE 8. Silkscreen Layer
20142988
FIGURE 9. Top Layer Pads
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18
LM4980
Revision History
Rev
Date
1.0
6/08/05
Initial release.
Description
1.1
6/29/05
Correct typographical and schematic errors.
Re-released D/S to the WEB.
1.2
7/18/05
Replaced curves 20142971 and 72 with 20142990 and 91 respectively, then re-released D/S to the WEB.
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LM4980 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier
for MP3 players
Physical Dimensions
inches (millimeters) unless otherwise noted
SD Package
Order Number LM4980SD
NS Package Number SDA10A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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