NSC LM4682

LM4682
10 Watt Stereo CLASS D Audio Power Amplifier with
Stereo Headphone Amplifier and DC Volume Control
General Description
Key Specifications
The LM4682 is a fully integrated single supply, high efficiency audio power amplifier solution. The LM4682 utilizes a
proprietary balanced pulse-width modulation technique that
lowers output noise and THD and improves PSRR when
compared to conventional pulse width modulators.
The LM4682 also features a stereo headphone amplifier that
delivers 60mW into a 32Ω headset with less than 0.5% THD.
The LM4682’s DC volume control has a +30dB to –48dB
range when speakers are driven and a range of +13dB to
–65dB when headphones are connected. All amplifiers are
protected by thermal shutdown. Additionally, all amplifiers
incorporate output current limiting function to protect their
outputs from short circuit.
n
n
n
n
n
n
n
The LM4682 features a low-power consumption shutdown
mode. And its efficiency reaches 85% for a 10W output
power with an 8Ω load. External heatsink is not required
when playing music. The IC features click and pop reduction
circuitry that minimizes audible popping during device
turn-on and turn-off. The LM4682 is available in a 48-lead
LLP package, ideal for portable and desktop computer applications.
PO at THD+N = 10%, VDD = 14V
10W (typ)
THD+N at 1kHz at 6W into 8Ω (Power Amp) 0.2% (typ)
Efficiency at 7W into 8Ω
84% (typ)
Total quiescent power supply current
52mA (typ)
Total shutdown power supply current
0.1mA (typ)
THD+N 1kHz, 20mW, 32Ω (Headphone)
0.02% (typ)
Single supply range
8.5V to 15V
Features
n
n
n
n
n
n
Pulse-width modulator.
DC Volume Control
Stereo headphone amplifier.
“Click and pop” suppression circuitry.
Micropower shutdown mode.
48 lead LLP package (No heatsink required).
Applications
n Flat Panel Displays
n Televisions
n Multimedia Monitors
Boomer ® is a registered trademark of National Semiconductor Corporation.
© 2006 National Semiconductor Corporation
DS201196
www.national.com
LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and
DC Volume Control
March 2006
LM4682
Block Diagram
20119622
Block Diagram for LM4682
www.national.com
2
LM4682
Connection Diagram
LLP Package
20119618
Top View
Order Number LM4682SQ
See NS Package Number SQA48A
(LLP Package)
3
www.national.com
www.national.com
4
Typical Application
Figure 1: Typical Stereo Audio Amplifier with Headphone Selection Circuit
20119621
LM4682
LLP Package
Vapor Phase (60 sec.)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
15.5V
Power Dissipation (Note 3)
Internally Limited
ESD Susceptibility (Note 4)
2000V
ESD Susceptibility (Note 5)
200V
Junction Temperature (Note 6)
Storage Temperature
220˚C
See AN-450 “Surface Mounting and their Effects on
Product Reliability” for other methods of soldering surface
mount devices.
−0.3V to VDD +0.3V
Input Voltage
215˚C
Infrared (15 sec.)
Operating Ratings (Notes 1, 2)
Temperature Range
150˚C
TMIN ≤ TA ≤ TMAX
−65˚C ≤ TA ≤ 150˚C
−40˚C ≤ TA ≤ +85˚C
8.5V ≤ VDD ≤ 15V
Supply Voltage
Thermal Resistance (LLP Package)
Soldering Information
θJA
28˚C/W
θJC
20˚C/W
Electrical Characteristics (Notes 1, 2, 7)
The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8Ω, LC filter values as shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
LM4682
Units
Typical
Max
Min
Operating Supply Voltage Range
12
15
8.5
Quiescent Power Supply Current,
VIN = 0VRMS, VHPSEL = 0V
Class D Mode
52
70
mA
Quiescent Power Supply Current,
VIN = 0VRMS, VHPSEL = 12V
Headphone Mode
30
40
mA
ISD
Quiescent Power Supply Current,
SDB = 0V
Shutdown Mode
0.1
VDD
IS
RIN
Input Resistance in Both Modes
VOLVDD
DC Reference Supply Voltage
VIH
Minimum Logic High Input
Voltage
VIL
Maximum Logic Low Input
Voltage
VHPIH
HP Sense High Input Voltage
VHPIL
HP Sense Low Input Voltage
V
mA
8
kΩ
5.5
3
V
0.7xVOLVDD
V
SDB, MUTEB pins
V
0.3xVOLVDD
VDD-1
VDD/2
V
V
Power Amplifiers
POR
Output Power, Per Channel
THD+N ≤ 1%, fIN = 1kHz
6.0
PD1
Power Dissipation
PO = 7W/Chan, fIN = 1kHz
2.6
W
EFF1
Efficiency
PO = 7W/Chan, fIN = 1kHz
84.4
%
THD+N
Harmonic Distortion + Noise
PO = 6W/Chan, fIN = 1kHz
0.2
%
Output Noise Voltage, RMS.
A−Weighted
RSOURCE = 50Ω, CIN = 1µF,
BW = 8Hz to 22kHz
A-weighted, input referred
13
µV
VNOISE
5.5
W
VRIPPLE = 200mVpp, 1kHz,
VIN = 0, input referred
f = 50Hz
PSRR
Power Supply Rejection Ratio
94
f = 60Hz
94
f 100Hz
93
f = 120Hz
93
f = 1kHz
84
dB
Headphone Amplifiers
5
www.national.com
LM4682
Absolute Maximum Ratings (Note 2)
LM4682
Electrical Characteristics (Notes 1, 2, 7)
(Continued)
The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8Ω, LC filter values as shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
Symbol
PO
Parameter
Power Out Per Channel
Conditions
LM4682
Typical
THD+N ≤ 1%, RL = 32Ω, fIN =
1kHz
Max
Min
80
60
Units
mW
THD+N
Distortion + Noise
PO = 20mW, RL = 32Ω, fIN =
1kHz
0.02
%
VNOISE
Output Noise Voltage, RMS
RIN = 50Ω, CIN = 1µF, BW =
20Hz to 20kHz
A-weighted, input referred
9
µV
PSRR
Power Supply Rejection Ratio
(Referred to Input)
200mV, 1kHz, VIN = 0, RL = 32Ω
88
dB
Electrical Characteristics for Volume Control (Notes 1, 2)
The following specifications apply for VDD = 12V. Limits apply for TA = 25˚C.
LM4682
Symbol
CRANGE
AM
Parameter
Gain Range
Mute Gain
Conditions
Units
(Limits )
Typical
(Note 8)
Limit
(Note 7)
VOL_CTL voltage = VOLVDD voltage,
No Load
Power Amplifier
Headphone Amplifier
30
13
29
12
dB (min)
dB (min)
VOL_CTL voltage = 0.069 x VOLVDD
No Load
Power Amplifier
Headphone Amplifier
–48
–65
–46
–63
dB (min)
dB (min)
VMUTE voltage = 0V, No Load
Power Amplifier
Headphone Amplifier
–80
–70
–60
–60
dB (max)
dB (max)
Note 1: All voltages are measured with respect to the ground 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: For operating at case temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance
of θJA = 28˚C/W (junction to ambient).
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Device pin 16 has ESD HBM rating = 1500V.
Note 5: Machine Model 220pF−240pF discharged through all pins.
Note 6: The operating junction temperature maximum is 150˚C.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Typicals are measured at 25˚C and represent the parametric norm.
www.national.com
6
LM4682
Typical Performance Characteristics (Power Amplifier)
THD+N vs Frequency
VDD = 12V, RL = 8Ω, PO = 1W
THD+N vs Frequency
VDD = 9V, RL = 8Ω, PO = 1W
20119658
20119659
THD+N vs Output Power Per Channel
VDD = 9V, fIN = 1kHz, RL = 8Ω
THD+N vs Frequency
VDD = 15V, RL = 8Ω, PO = 1W
20119661
20119660
THD+N vs Output Power Per Channel
VDD = 15V, fIN = 1kHz, RL = 8Ω
THD+N vs Output Power Per Channel
VDD = 12V, fIN = 1kHz, RL = 8Ω
20119662
20119663
7
www.national.com
LM4682
Typical Performance Characteristics (Power Amplifier)
THD+N vs Output Power Per Channel
VDD = 12V, fIN = 10kHz, RL = 8Ω
(Continued)
THD+N vs Output Power Per Channel
VDD = 12V, fIN = 20Hz, RL = 8Ω
20119664
20119665
Amplifiers Gain vs Frequency
VDD = 9V, RL = 8Ω, PO = 1W
Output Power vs Supply Voltage
fIN = 1kHz, RL = 8Ω
20119667
20119647
Amplifiers Gain vs Frequency
VDD = 15V, RL = 8Ω, PO = 1W
Amplifiers Gain vs Frequency
VDD = 12V, RL = 8Ω, PO = 1W
20119648
www.national.com
20119649
8
PSRR vs Frequency
VDD = 9V
LM4682
Typical Performance Characteristics (Power Amplifier)
(Continued)
PSRR vs Frequency
VDD = 12V
20119644
20119645
Class-D Amplifier Dissipation vs Load Dissipation
Per Channel, VDD = 9V, RL = 8Ω
(both channels driven and measured)
PSRR vs Frequency
VDD = 15V
20119638
20119646
Class-D Amplifier Dissipation vs Load Dissipation
Per Channel, VDD = 15V, RL = 8Ω
(both channels driven and measured)
Class-D Amplifier Dissipation vs Load Dissipation
Per Channel, VDD = 12V, RL = 8Ω
(both channels driven and measured)
20119640
20119639
9
www.national.com
LM4682
Typical Performance Characteristics (Power Amplifier)
Efficiency vs Output Power
VDD = 9V, RL = 8Ω
(both channels driven and measured)
Efficiency vs Output Power
VDD = 12V, RL = 8Ω
(both channels driven and measured)
20119641
20119642
Output Power vs Load Resistance
VDD = 9V, fIN = 1kHz
(both channels driven and measured)
Efficiency vs Output Power
VDD = 15V, RL = 8Ω
(both channels driven and measured)
20119643
20119655
Output Power vs Load Resistance
VDD = 15V, fIN = 1kHz
(both channels driven and measured)
Output Power vs Load Resistance
VDD = 12V, fIN = 1kHz
(both channels driven and measured)
20119657
20119656
www.national.com
(Continued)
10
LM4682
Typical Performance Characteristics (Power Amplifier)
(Continued)
Power Supply Current vs Power Supply Voltage
20119654
Typical Performance Characteristics (Headphone Amplifier)
THD+N vs Frequency
VDD = 12V, RL = 32Ω, PO = 20mW
THD+N vs Frequency
VDD = 9V, RL = 32Ω, PO = 20mW
20119651
20119652
THD+N vs Output Power
VDD = 9V, RL = 32Ω, fIN = 1kHz
THD+N vs Frequency
VDD = 15V, RL = 32Ω, PO = 20mW
20119668
20119653
11
www.national.com
LM4682
Typical Performance Characteristics (Headphone Amplifier)
THD+N vs Output Power
VDD = 12V, RL = 32Ω, fIN = 1kHz
THD+N vs Output Power
VDD = 15V, RL = 32Ω, fIN = 1kHz
20119669
20119670
Power Supply Current vs Power Supply Voltage
Output Power vs Supply Voltage Per Channel
fIN = 1kHz, RL = 32Ω
20119671
www.national.com
(Continued)
20119650
12
SYSTEM FUNCTIONAL INFORMATION
Modulation Technique
TABLE 1. Headphone Controls
Unlike typical Class D amplifiers that use single-ended comparators to generate a pulse-width modulated switching
waveform and RC timing circuits to set the switching frequency, the LM4682 uses a balanced differential floating
modulator. Oscillation is a result of injecting complimentary
currents onto the respective plates of a floating, on-die capacitor. The value of the floating capacitor and value of the
components in the modulator’s feedback network set the
nominal switching frequency at 450kHz. Modulation results
from imbalances in the injected currents. The amount of
current imbalance is directly proportional to the applied input
signal’s magnitude and frequency.
Using a balanced, floating modulator produces a Class D
amplifier that is immune to common mode noise sources
such as substrate noise. This noise occurs because of the
high frequency, high current switching in the amplifier’s output stage. The LM4682 is immune to this type of noise
because the modulator, the components that set its switching frequency, and even the load all float with respect to
ground.
The balanced modulator’s pulse width modulated output
drives the gates of the LM4682’s H-bridge configured output
power MOSFETs. The pulse-train present at the power
MOSFETs’ output is applied to an LC low pass filter that
removes the 450kHz energy component. The filter’s output
signal, which is applied to the driven load, is an amplified
replica of the audio input signal.
HP Sense Pin, HPSEL
Output Stage Configuration
0
Class D Amps Active
1
Class D Amps Inactive
Under Voltage Protection
The under voltage protection disables the output driver section of the LM4682 while the supply voltage is below 8V. This
condition may occur as power is first applied or during low
line conditions, changes in load resistance, or when power
supply sag occurs. The under voltage protection ensures
that all of the LM4682’s power MOSFETs are off. This action
eliminates shoot-through current and minimizes output transients during turn-on and turn-off. The under voltage protection gives the digital logic time to stabilize into known states,
further minimizing turn on output transients.
Power Supply Sequencing
In order to stabilize LM4682 before any operation, a
power-up sequence for the power supplies is recommended.
The Power VDD should be applied first. Without deactivating
the mute and shutdown function of the amplifiers, the
VOLVDD is then applied. Prior to removing the two supply
voltages, activate shutdown and mute.
Turn-On Time
The LM4682 has an internal timer that determines the amplifier’s turn-on time. After power is first applied or the part
returns from shutdown, the nominal turn-on time is 600ms.
This delay allows all externally applied capacitors to charge
to a final value of VDD/2. Further, during turn-on, the outputs
are muted. This minimizes output transients that may occur
while the part settles into its quiescent operating mode.
Shutdown Function
The LM4682’s active-low shutdown function allows the user
to place the amplifier in a shutdown mode while the system
power supply remains active. Activating shutdown stops the
output switching waveform and minimizes the quiescent current. Applying logic “0” to SDB pin enables the shutdown
function. Applying logic “1” to SDB pin disables the shutdown
function and restores full amplifier operation.
Output Stage Current Limit and Fault Detection
Protection
The output stage MOSFETs are protected against output
conditions that could otherwise compromise their operational
status. The first stage of protection is output current limiting.
When conditions that require high currents to drive a load,
the LM4682’s current limit circuitry clamps the output current
at a nominal value of 2.5A. The output waveform is present,
but may be clipped or its amplitude reduced. The same 2.5A
nominal current limit also occurs if the amplifier outputs are
shorted together or either output is shorted to VDD or GND.
The second stage of protection is an onboard fault detection
circuit that continuously monitors the signal on each output
MOSFET’s gate and compares it against the respective
drain voltage. When a condition is detected that violates a
MOSFET’s Safe Operating Area (SOA) and the drive signal
is disconnected from the output MOSFETs’ gates. The fault
detect circuit maintains this protective condition for approximately 600ms, at which time the drive signal is reconnected.
If the fault condition is no longer present, normal operation
resumes. If the fault condition remains, however, the drive
signal is again disconnected.
Mute Function
The LM4682’s active-low mute function allows the user to
place the amplifier outputs in muted mode while the amplifier’s analog input signals remain active. Activating mute internally removes the analog input signal from the Class D
and headphone amplifier inputs. While muted the amplifier
inputs and outputs retain in their VDD/2 operational bias.
Applying logic “0” to MUTEB pin activates mute. Applying
logic “1” to MUTEB pin deactivates mute. The MUTEB pin is
pull-down internally to put both Class D and headphone
amplifier outputs mute.
Stereo Headphone Amplifier
The LM4682’s stereo headphone amplifier operates continuously, even while the Class D amplifiers are active. When
using headphones to listen to program material, it is usually
desirable to stop driving external speakers. This is easily
achieved by using the active high HPSEL input. As shown in
typical application schematic in Figure 1, with no headphones connected to the headphone jack, the input voltage
applied to the HPSEL pin is a logic low. In this state, the
Class D amplifiers are active and able to drive external
speakers. When headphones are plugged into the headphone jack, the switch inside the jack is opened. This
13
www.national.com
LM4682
changes the voltage applied to the HPSEL pin to a logic
high, shutting off the LM4682’s Class D amplifiers. The
headphone control of the output configuration is shown in
Table 1.
General Features
LM4682
General Features
The LM4682 volume control consists of 31 steps, which are
individually selected by a variable DC voltage level on the
VOLCTL pin. The gain range of Class D amplifiers are from
–48dB to 30dB. The gain range of headphone amplifiers are
from –65dB to 13dB. Each gain step corresponds to specific
input voltage of both Class D amplifiers and headphone
amplifiers are shown in Table 2.
(Continued)
Thermal Protection
The LM4682 has thermal shutdown circuitry that monitors
the die temperature. Once the LM4682 die temperature
reaches 170˚C, the LM4682 disables the output switching
waveform and remains disabled until the die temperature
falls below 140˚C (typ).
To minimize the effect of noise on the volume control
VOLCTL pin, which can affect the selected gain level, hysteresis has been implemented. The amount of hysteresis
corresponds to half of the step width. For highest accuracy,
the voltage shown in the “recommended voltage” column of
the table is used to select a desired gain. The recommended
voltage is exactly halfway between the two closest transitions to the next highest or next lowest gain levels.
Over-Modulation Protection
The LM4682’s over-modulation protection is a result of the
preamplifier’s (AMP1 and AMP2, Figure 1) inability to produce signal magnitudes that equal the power supply voltages. Since the preamplifier’s output magnitude will always
be less than the supply voltage, the duty cycle of the amplifier’s switching output will never reach zero. Peak modulation is limited to a nominal 95%.
DC Volume Control
The LM4682 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the volume
control pin VOLCTL.
www.national.com
14
LM4682
General Features
(Continued)
TABLE 2. Volume Control Table
Step
Voltage Range (% of VOLVDD)
Voltage Range (V), VOLVDD = 5V
Low (%)
High (%)
Recommended (%)
Low (%)
High (%)
Recommended (%)
1
77.50%
100.00%
100.000%
3.875
5.000
5.000
2
75.00%
78.50%
76.875%
3.750
3.925
3.844
3
72.50%
76.25%
74.375%
3.625
3.813
3.719
4
70.00%
73.75%
71.875%
3.500
3.688
3.594
5
67.50%
71.25%
69.375%
3.375
3.563
3.469
6
65.00%
68.75%
66.875%
3.250
3.438
3.344
7
62.50%
66.25%
64.375%
3.125
3.313
3.219
8
60.00%
63.75%
61.875%
3.000
3.188
3.094
9
57.50%
61.25%
59.375%
2.875
3.063
2.969
10
55.00%
58.75%
56.785%
2.750
2.983
2.844
11
52.50%
56.25%
54.375%
2.625
2.813
2.719
12
50.00%
53.75%
51.875%
2.500
2.688
2.594
13
47.50%
51.25%
49.375%
2.375
2.563
2.469
14
45.00%
48.75%
46.875%
2.250
2.438
2.344
15
42.50%
46.25%
44.375%
2.125
2.313
2.219
16
40.00%
43.75%
41.875%
2.000
2.188
2.094
17
37.50%
41.25%
39.375%
1.875
2.063
1.969
18
35.00%
38.75%
36.875%
1.750
1.938
1.844
19
32.50%
36.25%
34.375%
1.625
1.813
1.719
20
30.00%
33.75%
31.875%
1.500
1.688
1.594
21
27.50%
31.25%
29.375%
1.375
1.563
1.469
22
25.00%
28.75%
26.875%
1.250
1.438
1.344
23
22.50%
26.25%
24.375%
1.125
1.313
1.219
24
20.00%
23.75%
21.875%
1.000
1.188
1.094
25
17.50%
21.25%
19.375%
0.875
1.063
0.969
26
15.00%
18.75%
16.875%
0.750
0.938
0.844
27
12.50%
16.25%
14.375%
0.625
0.813
0.719
28
10.00%
13.75%
11.875%
0.500
0.688
0.594
29
7.50%
11.25%
9.375%
0.375
0.563
0.469
30
5.00%
8.75%
6.875%
0.250
0.438
0.344
31
0.00%
6.25%
0.000%
0.000
0.313
0.000
15
www.national.com
LM4682
THD+N MEASUREMENTS AND OUT OF AUDIO BAND
NOISE
THD+N (Total Harmonic Distortion plus Noise) is a very
important parameter by which all audio amplifiers are measured. Often it is shown as a graph where either the output
power or frequency is changed over the operating range. A
very important variable in the measurement of THD+N is the
bandwidth-limiting filter at the input of the test equipment.
Class D amplifiers, by design, switch their output power
devices at a much higher frequency than the accepted audio
range (20Hz - 20kHz). Alternately switching the output voltage between VDD and GND allows the LM4682 to operate at
much higher efficiency than that achieved by traditional
Class AB amplifiers. Switching the outputs at high frequency
also increases the out-of-band noise. Under normal circumstances the output lowpass filter significantly reduces this
out-of-band noise. If the low pass filter is not optimized for a
given switching frequency, there can be significant increase
in out-of-band noise. THD+N measurements can be significantly affected by out-of-band noise, resulting in a higher
than expected THD+N measurement. To achieve a more
accurate measurement of THD, the test equipment’s input
bandwidth of the must be limited. Some common upper filter
points are 22kHz, 30kHz, and 80kHz. The input filter limits
the noise component of the THD+N measurement to a
smaller bandwidth resulting in a more real-world THD+N
value.
Application Hints
SUPPLY BYPASSING
The major source of noises to be taken care and applying
bypassing technique in using LM4682 are those transients
response coming from its output stage. During the switching
operations of the output stage of LM4682, the switching
frequencies vary when the internal modulator react to the
input signals. This creates a band of switching transients
giving back to the power supply terminals of LM4682. A
single capacitor may not bypass those transients well. Two
capacitors which values are closed to each other are used to
bypass this range of frequencies to the ground. 10µF tantalum capacitors and 4.7µF ceramic capacitors are needed for
this kind of decoupling of LM4682 switching operation. This
results an improvement in terms of both stability and audio
performance of LM4682. In addition, these capacitors should
be placed as close as possible to each IC’s supply pin(s)
using leads as short as possible. Apart from the power
supply de-coupling capacitors, the four bootstrapping capacitors (at pins BST1_A, BST2_A, BST1_B and BST2_B)
should also be placed close to their corresponding pins. This
could minimize the undesirable switching noise coupled to
the supply rail.
The LM4682 has two different sets of VDD pins: a set for
power VDD (PVDD_A and P VDD _B) and a set for signal VDD
_A and HP_ VDD. The parallel combination of the low value
ceramic (4.7µF) and high value tantalum (10µF) should be
used to bypass the power VDD pins. A small value (1µF)
ceramic or tantalum can be used to bypass the signal VDD
_A and HP_ VDD pin.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 2 through 6 show the recommended four-layer PCB
board layout that is optimized for the 48-pin LLP packaged
LM4682 and associated external components. This circuit is
designed for use with an external 12V supply and 8Ω speakers (or load resistors). Apply 12V and ground to board’s VDD
and GND terminals respectively. And apply 5V to the
VOLVDD (refer to power supply sequencing for details). Connect speakers (or load resistors) between the board’s
OUTA+ and OUTA-, and between the board’s OUTB+ and
OUTB-. Apply the stereo input signals to IN_A and IN_B.
When designing the layout of the PCB layout, please pay
attention to the output terminals of LM4682.
OUTPUT STAGE FILTERING
The LM4682 requires a low pass filter connected between
the amplifier’s bridge output and the load. Figure 1 shows
the recommended LC filter. A minimum value of 22µH is
recommended. As shown in Figure 1, using the values of the
components connected between the amplifier BTL outputs
and the load achieves a 2nd-order lowpass filter response
which optimizes the amplifier’s performance within the audio
band.
www.national.com
16
LM4682
Application Hints
(Continued)
20119626
Figure 2: Top Layer
20119627
Figure 3: Top Silkscreen Layer
17
www.national.com
LM4682
Application Hints
(Continued)
20119623
Figure 4: Upper Middle Layer
20119624
Figure 5: Lower Middle Layer
www.national.com
18
LM4682
Application Hints
(Continued)
20119625
Figure 6: Bottom Layer
19
www.national.com
LM4682
Revision History
www.national.com
Rev
Date
Description
1.1
6/02/05
Added the TSSOP pkg drawing, edited
the block diagram, input some texts and
limits values on the Electrical Char
table.
1.2
6/06/05
1) Replaced the Block Diagram per
Kevin H.
2) Edited CRANGErow (under Elect Char
for Volume table) (per Alex W.) MC
1.3
12/19/05
Added the Typical Appl Circuit Diagram,
General Features section, and the Appl
Hints section. Also input some texts
edits.
1.4
12/21/05
Changed the Block Diagram. Also input
some texts edits.
1.5
01/03/06
Replaced the Typ Appl Ckt Dg and the
Block Dg (per Alex.).
1.6
02/16/06
Added the Typical Perf. Curves and inpt
some text edits.
1.7
02/22/06
Input some text edits. Modified X-axes
on some of the curves.
Initial WEB release of the document.
1.8
02/24/06
Edited art 201196 71 (changed the
y-axis unit from mA to mW.
1.9
03/08/06
Did few texts clean-up and re-released
D/S to the WEB (per Kevin H.).
20
inches (millimeters) unless otherwise noted
Order Number LM4682SQ
NS Package Number SQA48A
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.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain
no ‘‘Banned Substances’’ as defined in CSP-9-111S2.
Leadfree products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
Email: [email protected]
Tel: 1-800-272-9959
www.national.com
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: [email protected]
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: [email protected]
Tel: 81-3-5639-7560
LM4682 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and
DC Volume Control
Physical Dimensions