LM4982
Ground-Referenced, Ultra Low Noise, 80mW Stereo
Headphone Amplifier with IntelliSense and I2C Volume
Control
General Description
The LM4982 is a ground referenced, variable gain audio
power amplifier capable of delivering 80mW of continuous
average power into a 16Ωsingle-ended load with less than
1% THD+N from a 3V power supply. The I
2
C volume control
allows +18 to -76 dB gain settings.
The LM4982 utilizes advanced charge pump technology to
generate the LM4982’s negative supply voltage. This elimi-
nates the need for output-coupling capacitors typically used
with single-ended loads.
IntelliSense is a new circuit technology that allows the
LM4982 to detect whether a mono or stereo headphone plug
has been inserted into the output jack.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4982 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli-
cations where minimal power consumption is a primary re-
quirement.
The LM4982 incorporates selectable low-power consump-
tion shutdown and channel select modes.
The LM4982 contains advanced pop & click circuitry that
eliminates noises which would otherwise occur during
turn-on and turn-off transitions.
Key Specifications
jImproved PSRR at 217Hz 66dB
jStereo Output Power at V
DD
= 3V,
R
L
=32Ω, THD+N = 1% 51mW (typ)
jShutdown current 0.1µA (typ)
Features
nGround referenced outputs
nI
2
C Volume and mode controls
nAvailable in space-saving micro SMD package
nUltra low current shutdown mode
nAdvanced pop & click circuitry eliminates noises during
turn-on and turn-off transitions
n1.6 – 4.0V operation
nNo output coupling capacitors, snubber networks,
bootstrap capacitors or gain-setting resistors required
nMono/Stereo headphone detect
Applications
nNotebook PCs
nDesktop PCs
nMobile Phones
nPDAs
nPortable electronic devices
nMP3 Players
Boomer®is a registered trademark of National Semiconductor Corporation.
July 2006
LM4982 Ground-Referenced, Ultra Low Noise, 80mW Stereo Headphone Amplifier with
IntelliSense and I2C Volume Control
© 2006 National Semiconductor Corporation DS201614 www.national.com
Typical Application
20161466
FIGURE 1. Typical Audio Amplifier Application Circuit
LM4982
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Connection Diagrams
micro SMD Package micro SMD Marking
20161459
Top View
Order Number LM4982TL
20161401
Top View
XY - Date Code
TT - Lot Traceability
GG3 – LM4982
See NS Package Number LM4982TL
Pin Descriptions
Pin Designator Pin Name Pin Function
A1 SGND Amplifier ground
A2 HPE Headphone sende input
A3 PV
DD
Charge pump / digital power supply
A4 C
CP+
Charge pump fly capacitor positive side
B1 OUT_L Left channel output
B2 IN_L Left channel input
B3 I
2
C_V
DD
I
2
C power supply
B4 PGND Charge pump / digital ground
C1 SV
SS
Amplifier negative supply
C2 IN_R Right channel input
C3 SCL I
2
C SCL line
C4 C
CP-
Charge pump fly capacitor negative side
D1 OUT_R Right channel output
D2 SV
DD
Amplifier positive supply
D3 SDA I
2
C SDA line
D4 CP
OUT
Charge pump power output
LM4982
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Absolute Maximum Ratings (Note 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage 4.5V
Storage Temperature −65˚C to +150˚C
Input Voltage −0.3V to V
DD
+0.3V
Power Dissipation (Note 3) Internally Limited
ESD Susceptibility (Note 4) 2000V
ESD Susceptibility (Note 5) 200V
Junction Temperature 150˚C
Thermal Resistance
θ
JA
(typ) - (TLA16XXX) 105˚C/W (Note X)
Operating Ratings
Temperature Range
T
MIN
≤T
A
≤T
MAX
−40˚C ≤T
A
≤+85˚C
Supply Voltage 1.6V ≤V
DD
≤4.0V
Audio Amplifier Electrical Characteristics V
DD
=3V(Notes 1, 2)
The following specifications apply for V
DD
= 3V, R
L
=16Ω,A
V
= 0dB, unless otherwise specified. Limits apply for T
A
= 25˚C.
Symbol Parameter Conditions LM4982 Units
(Limits)
Typical
(Note 6)
Limits (Notes 7,
8)
I
DD
Quiescent Power Supply
Current Full Power Mode
V
IN
= 0V, inputs terminated,
both channels enabled 8.1 11.5 mA (max)
V
IN
= 0V, inputs terminated,
one channel enabled 5.1 7.3 mA
V
IN
= 0V, inputs terminated,
No headphone inserted 2.15 mA
I
SD
Shutdown Current With SD enabled 0.1 1.5 µA (max)
V
OS
Output Offset Voltage R
L
=32Ω0.7 4.5 mV (max)
A
V
Gain Max and Min settings [B0:B4] = 00000 –70 dB
[B0:B4] = 11111 +18 dB
R
IN
Input Resistance gain setting 18dB 22 15
29
kΩ(min)
kΩ(max)
gain setting –76dB 200 kΩ
P
OUT
Stereo Output Power
THD+N = 1% (max); f = 1kHz,
R
L
=16Ω, per channel
47 40 mW (min)
THD+N = 1% (max); f = 1kHz,
R
L
=32Ω, per channel
51 mW
THD+N Total Harmonic Distortion +
Noise
P
O
= 50mW, f = 1kHz
R
L
=16Ω, single channel
0.05
%
P
O
= 50mW, f = 1kHz
R
L
=32Ω, single channel
0.025
PSRR Power Supply Rejection Ratio
Full Power Mode
V
RIPPLE
= 200mV
P-P
, input referred
f = 217Hz 66 56
dBf = 1kHz 55
f = 20kHz 40
SNR Signal-to-Noise-Ratio R
L
=32Ω,P
OUT
= 20mW,
f = 1kHz, BW = 20Hz to 22kHz 100 dB
T
WU
Wake Up Time From
Shutdown Charge Pump Wake-Up Time 300 µs
T
WU
Wake Up Time Headphone Sense Debounce Time 200 ms
X
TALK
Crosstalk R
L
=16Ω,P
OUT
= 1.6mW,
f = 1kHz, A-weighted filter 70 dB
Z
OUT
Output Impedance In Shutdown Mode 180 kΩ
I
L
Input Leakage ±0.1 nA
Vih HPS in threshold 0.9xV
DD
[min] V
Vil HPS in threshold 0.7xV
DD
[max] V
LM4982
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Audio Amplifier Electrical Characteristics V
DD
=3V(Notes 1, 2) (Continued)
The following specifications apply for V
DD
= 3V, R
L
=16Ω,A
V
= 0dB, unless otherwise specified. Limits apply for T
A
= 25˚C.
Symbol Parameter Conditions LM4982 Units
(Limits)
Typical
(Note 6)
Limits (Notes 7,
8)
R
INT
Intellisense Threshold
Resistance 63
9
Ω(min)
Ω(max)
Control Interface Electrical Characteristics (Notes 1, 2)
The following specifications apply for 1.6V <V
DD
<4.0V, unless otherwise specified. Limits apply for T
A
= 25˚C.
Symbol Parameter Conditions LM4982 Units
(Limits)
Typical
(Note 6)
Limits (Notes 7,
8)
t
1
SCL period 2.5 µs (min)
t
2
SDA Setup Time 100 ns (min)
t
3
SDA Stable Time 0 ns (min)
t
4
Start Condition Time 100 ns (min)
t
5
Stop Condition Time 100 ns (min)
V
IH
0.7xI
2
CV
DD
V (min)
V
IL
0.3xI
2
CV
DD
V (max)
Note 1: All voltages are measured with respect to the GND pin unless otherwise specified.
Note 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 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 3: 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 =(T
JMAX -T
A)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4982, see power
derating currents for more information.
Note 4: Human body model, 100pF discharged through a 1.5kΩresistor.
Note 5: Machine Model, 220pF - 240pF discharged through all pins.
Note 6: Typicals are measured at +25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
LM4982
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Typical Performance Characteristics
THD+N vs Frequency
V
DD
= 1.8V, R
L
=16Ω,
P
O
= 7mW, Mono
THD+N vs Frequency
V
DD
= 1.8V, R
L
=16Ω,
P
O
= 2mW, Stereo
20161475 20161474
THD+N vs Frequency
V
DD
= 1.8V, R
L
=32Ω,
P
O
= 7mW, Mono
THD+N vs Frequency
V
DD
= 1.8V, R
L
=32Ω,
P
O
= 2mW, Stereo
20161477 20161476
THD+N vs Frequency
V
DD
= 3V, R
L
=16Ω,
P
O
= 50mW, Mono
THD+N vs Frequency
V
DD
= 3V, R
L
=16Ω,
P
O
= 25mW, Stereo
20161482 20161483
LM4982
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Typical Performance Characteristics (Continued)
THD+N vs Frequency
V
DD
= 3V, R
L
=32Ω,
P
O
= 50mW, Mono
THD+N vs Frequency
V
DD
= 3V, R
L
=32Ω,
P
O
= 25mW, Stereo
20161484 20161485
THD+N vs Frequency
V
DD
= 3.6V, R
L
=16Ω,
P
O
= 100mW, Mono
THD+N vs Frequency
V
DD
= 3.6V, R
L
=16Ω,
P
O
= 60mW, Stereo
20161478 20161479
THD+N vs Frequency
V
DD
= 3.6V, R
L
=32Ω,
P
O
= 100mW, Mono,
THD+N vs Frequency
V
DD
= 3.6V, R
L
=32Ω,
P
O
= 60mW, Stereo
20161480 20161481
LM4982
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Typical Performance Characteristics (Continued)
THD+N vs Output Power
V
DD
= 1.8V, R
L
=16Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 1.8V, R
L
=16Ω,
f = 1kHz, Stereo
20161486 20161487
THD+N vs Output Power
V
DD
= 1.8V, R
L
=32Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 1.8V, R
L
=32Ω,
f = 1kHz, Stereo
20161488 20161489
THD+N vs Output Power
V
DD
= 3V, R
L
=16Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 3V, R
L
=16Ω,
f = 1kHz, Stereo
20161494 201614B2
LM4982
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Typical Performance Characteristics (Continued)
THD+N vs Output Power
V
DD
= 3V, R
L
=32Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 3V, R
L
=32Ω,
f = 1kHz, Stereo
20161495 20161496
THD+N vs Output Power
V
DD
= 3.6V, R
L
=16Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 3.6V, R
L
=16Ω,
f = 1kHz, Stereo
20161490 20161491
THD+N vs Output Power
V
DD
= 3.6V, R
L
=32Ω,
f = 1kHz, Mono
THD+N vs Output Power
V
DD
= 3.6V, R
L
=32Ω,
f = 1kHz, Stereo
20161492 20161493
LM4982
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Typical Performance Characteristics (Continued)
Power Dissipation vs Output Power
V
DD
= 1.8V, R
L
=16Ω, f = 1kHz
Power Dissipation vs Output Power
V
DD
= 1.8V, R
L
=32Ω, f = 1kHz
20161497 20161498
Power Dissipation vs Output Power
V
DD
= 3V, R
L
=16Ω, f = 1kHz
Power Dissipation vs Output Power
V
DD
= 3V, R
L
=32Ω, f = 1kHz
201614A4 201614A5
Power Dissipation vs Output Power
V
DD
= 3.6V, R
L
=16Ω, f = 1kHz
Power Dissipation vs Output Power
V
DD
= 3.6V, R
L
=32Ω, f = 1kHz
201614A2 201614A3
LM4982
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Typical Performance Characteristics (Continued)
Output Power vs Power Supply Voltage
R
L
=16Ω, f = 1kHz, Mono
Output Power vs Power Supply Voltage
R
L
=16Ω, f = 1kHz, Stereo
201614B5 201614B6
Output Power vs Power Supply Voltage
R
L
=32Ω, f = 1kHz, Mono
Output Power vs Power Supply Voltage
R
L
=32Ω, f = 1kHz, Stereo
201614B7 201614B8
Power Supply Current vs Power Supply Voltage
V
IN
= 0V, Mono
Power Supply Current vs Power Supply Voltage
V
IN
= 0V, Stereo
201614A6 201614A7
LM4982
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Typical Performance Characteristics (Continued)
PSRR vs Frequency
V
DD
= 1.8V, Vripple = 200mVp-p
PSRR vs Frequency
V
DD
= 3V, Vripple = 200mVp-p
201614A8 201614B1
PSRR vs Frequency
V
DD
= 3.6V, Vripple = 200mVp-p
Crosstalk
V
DD
= 3V, RL = 16Ω,P
O
= 50mW
201614B0 201614B3
Crosstalk
V
DD
= 3V, RL = 32Ω,P
O
= 50mW
201614B4
LM4982
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Application Information
TABLE 1. Chip Address
D7 D6 D5 D4 D3 D2 D1 D0
Chip Address 11101100
TABLE 2. Control Registers
D7 D6 D5 D4 D3 D2 D1 D0
Mode Control 0000CD3CD2CD1CD0
Volume Control 1 0 0 VD4 VD3 VD2 VD1 VD0
TABLE 3. Mode Control
CD3 1 Intellisense Enabled
0 Intellisense Disabled
CD2 1 Mute Enabled
0 Mute Disabled
CD1 1 Stereo
0 Mono *
CD0 1 Normal Operation
0 Shutdown Enabled
* Mono mode mixes (Left + Right) / 2, into Left output
I
2
C VOLUME CONTROL
The LM4982 can be configured in 32 different gain steps by forcing I2C volume control bits to a desired gain according to the table
below:
20161468
FIGURE 2. I
2
C Bus Format
20161467
FIGURE 3. I
2
C Timing Diagram
LM4982
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Application Information (Continued)
TABLE 4. Volume Control
VD4 VD3 VD2 VD1 VD0 Gain (dB)
00000 –70
00001 –60
00010 –52
00011 –44
00100 –38
00101 –34
00110 –30
00111 –27
01000 –24
01001 –21
01010 –18
01011 –16
01100 –14
01101 –12
01110 –10
01111 –8
10000 –6
10001 –4
10010 –2
10011 0
10100 2
10101 4
10110 6
10111 8
11000 10
11001 12
11010 13
11011 14
11100 15
11101 16
11110 17
11111 18
LM4982
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Application Information (Continued)
HP SENSE FUNCTION
Connecting headphones to the headphone jack disconnects
the headphone jack contact pin from OUT_L and allows Rpu
to pull the HP Sense pin up to V
DD
. This enables the device.
A microprocessor or a switch can replace the headphone
jack contact pin.
Shutdown
(Bit CD0)
HPS pin Operational Mode
Logic High Logic Low Standby Mode
Logic High Logic High Full Power Mode
Logic Low Logic Low Micro-Power Shutdown
Logic Low Logic High Micro-Power Shutdown
INTELLISENSE
National’s Intellisense technology allows the LM4982 to de-
tect whether a mono or stereo headphone has been inster-
ted in to the headphone jack. If a mono headphone is
inserted into a device that is designed for a stereo head-
phone, one of the amplifiers will be shorted to ground. With-
out Intellisense, this may damage the device or, best case,
the device will draw excessive current, shortening battery
life.
Intellisense works by first waiting for one of the following
events:
•When the device powers up, if a headphone is already
inserted
•When a headphone is inserted, if the device is already
powered up
•After the thermal shutdown circuitry is activated.
The occurrence of one of these events triggers the Intel-
lisense circuitry to apply a small voltage on both left and right
outputs and sense the resulting current through the load. If
the load connected to the amplifier is greater than 9Ω, the
amplifier driving it will be in full power mode. If the load is
less than 3Ω, the LM4982 will assume a short to ground and
shutdown the driving amplifier. Intellisense puts the LM4982
in mono mode when the right channel is shorted. For extra
protection both amplifiers will be shutdown when the left
channel is shorted to ground. The Intellisense feature can be
enabled and disabled through an I2C command.
This Intellisense feature is designed for headphones with a
nominal impedance of 16Ωor greater, using lower imped-
ance loads may cause this feature to operate incorrectly.
MONO/STEREO OPERATION
When Intellisense is disabled the value of the CD1 bit of the
mode control determines if the LM4982 is in mono or stereo
mode. When the LM4982 is in mono mode the left and right
input signals are mixed to the left channel amplifier and
attenuated by -6dB. The right channel amplifier is put in
shutdown to save power. The mixing function allows full
reproduction of a stereo input signal in a mono headphone
and optimum headroom is kept by attenuating by a factor of
two.
I
2
C COMPATIBLE INTERFACE
The LM4982 uses a serial bus, which conforms to the I
2
C
protocol, to control the chip’s functions with two wires: clock
(SCL) and data (SDA). The clock line is uni-directional. The
data line is bi-directional (open-collector). The maximum
clock frequency specified by the I
2
C standard is 400kHz. In
this discussion, the master is the controlling microcontroller
and the slave is the LM4982.
The bus format for the I
2
C interface is shown in Figure 2. The
bus format diagram is broken up into six major sections:
The "start" signal is generated by lowering the data signal
while the clock signal is high. The start signal will alert all
devices attached to the I
2
C bus to check the incoming ad-
dress against their own address.
The 8-bit chip address is sent next, most significant bit first.
The data is latched in on the rising edge of the clock. Each
address bit must be stable while the clock level is high.
After the last bit of the address bit is sent, the master
releases the data line high (through a pull-up resistor). Then
the master sends an acknowledge clock pulse. If the
LM4982 has received the address correctly, then it holds the
data line low during the clock pulse. If the data line is not
held low during the acknowledge clock pulse, then the mas-
ter should abort the rest of the data transfer to the LM4982.
The 8 bits of data are sent next, most significant bit first.
Each data bit should be valid while the clock level is stable
high.
After the data byte is sent, the master must check for another
acknowledge to see if the LM4982 received the data.
If the master has more data bytes to send to the LM4982,
then the master can repeat the previous two steps until all
data bytes have been sent.
The "stop" signal ends the transfer. To signal "stop", the data
signal goes high while the clock signal is high. The data line
should be held high when not in use.
201614A1
FIGURE 4.
20161460
FIGURE 5.
LM4982
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Application Information (Continued)
I
2
C INTERFACE POWER SUPPLY PIN (I
2
CV
DD
)
The LM4982’s I
2
C interface is powered up through the
I
2
CV
DD
pin. The LM4982’s I
2
C interface operates at a volt-
age level set by the I
2
CV
DD
pin which can be set indepen-
dent to that of the main power supply pin V
DD
. This is ideal
whenever logic levels for the I
2
C interface are dictated by a
microcontroller or microprocessor that is operating at a lower
supply voltage than the main battery of a portable system.
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 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
presence does not eliminate the need for a local 1.0µF
tantalum bypass capacitance connected between the
LM4982’s supply pins and ground. Keep the length of leads
and traces that connect capacitors between the LM4982’s
power supply pins and ground as short as possible.
ELIMINATING THE OUTPUT COUPLING CAPACITOR
The LM4982 features a low noise inverting charge pump that
generates an internal negative supply voltage. This allows
the outputs of the LM4982 to be biased about GND instead
of a nominal DC voltage, like traditional headphone amplifi-
ers. Because there is no DC component, the large DC
blocking capacitors (typically 220µF) are not necessary. The
coupling capacitors are replaced by two, small ceramic
charge pump capacitors, saving board space and cost.
Eliminating the output coupling capacitors also improves low
frequency response. In traditional headphone amplifiers, the
headphone impedance and the output capacitor form a high
pass filter that not only blocks the DC component of the
output, but also attenuates low frequencies, impacting the
bass response. Because the LM4982 does not require the
output coupling capacitors, the low frequency response of
the device is not degraded by external components.
In addition to eliminating the output coupling capacitors, the
ground referenced output nearly doubles the available dy-
namic range of the LM4982 when compared to a traditional
headphone amplifier operating from the same supply volt-
age.
OUTPUT TRANSIENT (’CLICK AND POPS’)
ELIMINATED
The LM4982 contains advanced circuitry that virtually elimi-
nates output transients (’clicks and pops’). This circuitry
prevents all traces of transients when the supply voltage is
first applied or when the part resumes operation after coming
out of shutdown mode.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. Equation 1 states the maximum power
dissipation point for a single-ended amplifier operating at a
given supply voltage and driving a specified output load.
P
DMAX
= (2V
DD
)
2
/(2π
2
R
L
) (1)
Since the LM4982 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. Even
with large internal power dissipation, the LM4982 does not
require heat sinking over a large range of ambient tempera-
tures. The maximum power dissipation point obtained must
not be greater than the power dissipation that results from
Equation 2:
P
DMAX
=(T
JMAX
-T
A
)/(θ
JA
) (2)
For the micro SMD package, θ
JA
= 105˚C/W. T
JMAX
= 150˚C
for the LM4982. Depending on the ambient temperature, T
A
,
of the system surroundings, Equation 2 can be used to find
the maximum internal power dissipation supported by the IC
packaging. If the result of Equation 1 is greater than that of
Equation 2, then either the supply voltage must be de-
creased, the load impedance increased or T
A
reduced.
Power dissipation is a function of output power and thus, if
typical operation is not around the maximum power dissipa-
tion point, the ambient temperature may be increased ac-
cordingly.
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4982’s performance requires properly se-
lecting external components. Though the LM4982 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
Charge Pump Capacitor Selection
Use low ESR (equivalent series resistance) (<100mΩ) ce-
ramic capacitors with an X7R dielectric for best perfor-
mance. Low ESR capacitors keep the charge pump output
impedance to a minimum, extending the headroom on the
negative supply. Higher ESR capacitors result in reduced
output power from the audio amplifiers.
Charge pump load regulation and output impedance are
affected by the value of the flying capacitor (C1). A larger
valued C1 (up to 3.3uF) improves load regulation and mini-
mizes charge pump output resistance. Beyond 3.3uF, the
switch-on resistance dominates the output impedance for
capacitor values above 2.2uF.
The output ripple is affected by the value and ESR of the
output capacitor (C2). Larger capacitors reduce output ripple
on the negative power supply. Lower ESR capacitors mini-
mize the output ripple and reduce the output impedance of
the charge pump.
The LM4982 charge pump design is optimized for 2.2uF, low
ESR, ceramic, flying, and output capacitors.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitors (C
i
in Figure 1). A high value ca-
pacitor can be expensive and may compromise space effi-
ciency in portable designs. In many cases, however, the
speakers used in portable systems, whether internal or ex-
ternal, have little ability to reproduce signals below 150Hz.
Applications using speakers with this limited frequency re-
sponse reap little improvement by using high value input and
output capacitors.
Besides affecting system cost and size, C
i
has an effect on
the LM4982’s click and pop performance. The magnitude of
the pop is directly proportional to the input capacitor’s size.
LM4982
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Application Information (Continued)
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 1, the internal input resistor, R
i
and the
input capacitor, C
i
, produce a -3dB high pass filter cutoff
frequency that is found using Equation (3). Conventional
headphone amplifiers require output capacitors; Equation (3)
can be used, along with the value of R
L
, to determine to-
wards the value of output capacitor needed to produce a
–3dB high pass filter cutoff frequency.
f
i-3dB
=1/2πR
i
C
i
(3)
Also, careful consideration must be taken in selecting a
certain type of capacitor to be used in the system. Different
types of capacitors (tantalum, electrolytic, ceramic) have
unique performance characteristics and may affect overall
system performance. (See the section entitled Charge Pump
Capacitor Selection.)
LM4982
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Demo Board Artwork
201614A0
Top Layer
20161470
Mid Layer 1
LM4982
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Demo Board Artwork (Continued)
20161471
Mid Layer 2
20161469
Bottom Layer
LM4982
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Revision History
Rev Date Description
1.0 2/09/06 Initial WEB release.
1.1 7/27/06 Edited the mktg outline descriptions (X1, X2, and
X3), then re-released the D/S to the WEB per
Nisha P.
LM4982
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Physical Dimensions inches (millimeters) unless otherwise noted
16-Bump micro SMD
Order Number LM4982TL
NS Package Number TLA1611A
X
1
= 1.965 ±0.03 X
2
= 1.965 ±0.03 X
3
= 0.6 ±0.075
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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in a significant injury to the user.
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device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
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LM4982 Ground-Referenced, Ultra Low Noise, 80mW Stereo Headphone Amplifier with
IntelliSense and I2C Volume Control
