LM4924
2 Cell Battery, 40mW Per Channel Output Capacitor-Less
(OCL) Stereo Headphone Audio Amplifier
General Description
Key Specifications
The LM4924 is a Output Capacitor-Less (OCL) stereo headphone amplifier, which when connected to a 3.0V supply,
delivers 40mW per channel to a 16Ω load with less than 1%
THD+N.
With the LM4924 packaged in the MM and SD packages, the
customer benefits include low profile and small size. These
packages minimizes PCB area and maximizes output power.
The LM4924 features circuitry that reduces output transients
(“clicks” and “pops”) during device turn-on and turn-off, and
Mute On and Off. An externally controlled, low-power consumption, active-low shutdown mode is also included in the
LM4924. Boomer audio power amplifiers are designed specifically to use few external components and provide high
quality output power in a surface mount packages.
n
n
n
n
n
OCL output power
(RL = 16Ω, VDD = 3.0V, THD+N = 1%)
40mW (typ)
Micropower shutdown current
0.1µA (typ)
Supply voltage operating range
1.5V < VDD < 3.6V
PSRR 100Hz, VDD = 3.0V, AV = 2.5
66dB (typ)
Features
2-cell 1.5V to 3.6V battery operation
OCL mode for stereo headphone operation
Unity-gain stable
“Click and pop” suppression circuitry for shutdown On
and Off transients
n Active low micropower shutdown
n Thermal shutdown protection circuitry
n
n
n
n
Applications
n Portable two-cell audio products
n Portable two-cell electronic devices
Typical Application
20121057
FIGURE 1. Block Diagram
Boomer ® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS201210
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LM4924 2 Cell Battery, 40mW Per Channel Output Capacitor-Less (OCL) Stereo Headphone Audio
Amplifier
October 2004
LM4924
Connection Diagrams
MSOP Package
MSOP Marking
20121006
Z- Plant Code
X - Date Code
T - Die Traceability
G - Boomer Family
B7 - LM4924MM
20121058
Top View
Order Number LM4924MM
See NS Package Number MUB10A for MSOP
SD Package
SD Marking
20121007
Z - Plant Code
X - Date Code
T - Die Traceability
Bottom Line - Part Number
20121052
Top View
Order Number LM4924SD
See NS Package Number SDA10A
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2
LM4924
Typical Connections
20121059
FIGURE 2. Typical OCL Output Configuration Circuit
3
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LM4924
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.
3.8V
Thermal Resistance
−65˚C to +150˚C
θJA (typ) MUB10A
175˚C/W
−0.3V to VDD +0.3V
θJA (typ) SDA10A
73˚C/W
Supply Voltage
Storage Temperature
Input Voltage
220˚C
Power Dissipation (Note 2)
Internally limited
ESD Susceptibility(Note 3)
2000V
ESD Susceptibility on pin 7, 8, and
9 (Note 3)
Operating Ratings
Temperature Range
2kV
ESD Susceptibility (Note 4)
TMIN ≤ TA ≤ TMAX
200V
Junction Temperature
−40˚C ≤ TA ≤ +85˚C
1.5V ≤ VDD ≤ 3.6V
Supply Voltage
150˚C
Solder Information
Small Outline Package Vapor
Phase (60sec)
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 = 2.5, RL =
16Ω.Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
LM4924
Typical
Limit
(Note 6)
(Note 7)
1.9
IDD
Quiescent Power Supply Current VIN = 0V, IO = 0A, RL = ∞ (Note 8)
1.5
ISD
Shutdown Current
0.1
1
VOS
Output Offset Voltage
1
10
PO
Output Power (Note 9)
40
30
VNO
Output Voltage Noise
VSHUTDOWN = GND
Units
(Limits)
mA (max)
µA (max)
mV (max)
f = 1kHz, per channel
OCL (Figure 2), THD+N = 1%
mW (min)
20Hz to 20kHz, A-weighted, Figure 2
13
THD
PO = 10mW
0.1
0.5
%
Crosstalk
Freq = 1kHz
45
35
dB (min)
Freq = 100Hz, OCL
66
58
dB (min)
230
0.7VDD
V (min)
0.3VDD
V (max)
70
dB
VRIPPLE = 200mVP-P sine wave
PSRR
Power Supply Rejection Ratio
TWAKE-UP
Wake-Up Time
1.5V ≤ VDD ≤ 3.6V, Fig 2
VIH
Control Logic High
1.5V ≤ VDD ≤ 3.6V
VIL
Control Logic Low
Mute
Attenuation
µVRMS
msec
1.5V ≤ VDD ≤ 3.6V
1VPP Reference, RIN = 20k, RFB = 50k
90
Electrical Characteristics VDD = 1.8V (Notes 1, 5)
The following specifications apply for the circuit shown in Figure 2, unless otherwise specified. AV = 2.5, RL = 16Ω.
Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
= 0V, IO = 0A, RL = ∞ (Note 8)
IDD
Quiescent Power Supply Current
VIN
ISD
Shutdown Current
VSHUTDOWN = GND
VOS
Output Offset Voltage
LM4924
Typical
Limit
(Note 6)
(Note 7)
1.4
0.1
Units
(Limits)
mA (max)
µA (max)
1
mV (max)
f = 1kHz
PO
Output Power (Note 9)
OCL Per channel, Fig. 2, Freq = 1kHz
THD+N = 1%
10
mW
VNO
Output Voltage Noise
20Hz to 20kHz, A-weighted, Figure 2
10
µVRMS
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(Continued)
The following specifications apply for the circuit shown in Figure 2, unless otherwise specified. AV = 2.5, RL = 16Ω.
Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
LM4924
Typical
Limit
(Note 6)
(Note 7)
Units
(Limits)
THD
PO = 5mW
0.1
%
Crosstalk
Freq = 1kHz
45
dB (min)
66
dB
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVP-P sine wave
Freq = 100Hz, OCL
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 and must be derated at elevated temperatures. The maximum
allowable power dissipation is PDMAX = (TJMAX − TA)/θJA. For the LM4924, 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, 220pF–240pF 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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LM4924
Electrical Characteristics VDD = 1.8V (Notes 1, 5)
LM4924
Typical Performance Characteristics
THD+N vs Frequency
VDD = 1.8V, PO = 5mW, RL = 32Ω
THD+N vs Frequency
VDD = 1.8V, PO = 5mW, RL = 16Ω
20121013
20121014
THD+N vs Frequency
VDD = 3.0V, PO = 10mW, RL = 32Ω
THD+N vs Frequency
VDD = 3.0V, PO = 10mW, RL = 16Ω
20121015
20121016
THD+N vs Output Power
VDD = 1.8V, RL = 32Ω, f = 1kHz
THD+N vs Output Power
VDD = 1.8V, RL = 16Ω, f = 1kHz
20121017
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20121018
6
LM4924
Typical Performance Characteristics
(Continued)
THD+N vs Output Power
VDD = 3.0V, RL = 16Ω, f = 1kHz
THD+N vs Output Power
VDD = 3.0V, RL = 32Ω, f = 1kHz
20121019
20121020
Power Supply Rejection Ratio
VDD = 3.0V, RL = 16Ω,
Vripple = 200mVp-p, Input Terminated into 10Ω load
Power Supply Rejection Ratio
VDD = 1.8V, RL = 16Ω,
Vripple = 200mVp-p, Input Terminated into 10Ω load
20121011
20121012
Noise Floor
VDD = 3.0V, RL = 16Ω
Noise Floor
VDD = 1.8V, RL = 16Ω
20121009
20121010
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LM4924
Typical Performance Characteristics
(Continued)
VDD
VDD
Channel Sepration
RL = 16Ω
20121008
20121021
Output Power vs Supply Voltage
RL = 32Ω, from top to bottom:
THD+N = 10%; THD+N = 1%
Output Power vs Supply Voltage
RL = 16Ω, from top to bottom:
THD+N = 10%; THD+N = 1%
20121022
20121023
Power Dissipation vs Output Power
VDD = 3.0V, f = 1kHz, from top to bottom:
RL = 16Ω; RL = 32Ω
Power Dissipation vs Output Power
VDD = 1.8V, f = 1kHz, from top to bottom:
RL = 16Ω; RL = 32Ω
20121024
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Output Power vs Load Resistance
f = 1kHz. from top to bottom:
= 3.0V, 10%THD+N; VDD = 3.0V, 1%THD+N
= 1.8V, 10%THD+N; VDD = 1.8V, 1%THD+N
20121025
8
LM4924
Typical Performance Characteristics
(Continued)
Supply Current vs Supply Voltage
20121026
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LM4924
of CBYPASS and the turn-on time. Here are some typical
turn-on times for various values of CBYPASS.
Application Information
ELIMINATING OUTPUT COUPLING CAPACITORS
AMPLIFIER CONFIGURATION EXPLANATION
Typical single-supply audio amplifiers that drive singleended (SE) headphones use a coupling capacitor on each
SE output. This output coupling capacitor blocks the halfsupply voltage to which the output amplifiers are typically
biased and couples the audio signal to the headphones. The
signal return to circuit ground is through the headphone
jack’s sleeve.
The LM4924 eliminates these output coupling capacitors.
VoC is internally configured to apply a 1/2VDD bias voltage to
a stereo headphone jack’s sleeve. This voltage matches the
quiescent voltage present on the VoA and VoB outputs that
drive the headphones. The headphones operate in a manner
similar to a bridge-tied-load (BTL). The same DC voltage is
applied to both headphone speaker terminals. This results in
no net DC current flow through the speaker. AC current flows
through a headphone speaker as an audio signal’s output
amplitude increases on the speaker’s terminal.
As shown in Figure 1, the LM4924 has three operational
amplifiers internally. Two of the amplifier’s have externally
configurable gain while the other amplifier is internally fixed
at the bias point acting as a unity-gain buffer. The closedloop gain of the two configurable amplifiers is set by selecting the ratio of Rf to Ri. Consequently, the gain for each
channel of the IC is
AV = -(Rf/Ri)
By driving the loads through outputs VO1 and VO2 with VO3
acting as a buffered bias voltage the LM4924 does not
require output coupling capacitors. The typical single-ended
amplifier configuration where one side of the load is connected to ground requires large, expensive output coupling
capacitors.
A configuration such as the one used in the LM4924 has a
major advantage over single supply, single-ended amplifiers.
Since the outputs VO1, VO2, and VO3 are all biased at 1/2
VDD, no net DC voltage exists across each load. This eliminates the need for output coupling capacitors that are required in a single-supply, single-ended amplifier configuration. Without output coupling capacitors in a typical singlesupply, single-ended amplifier, the bias voltage is placed
across the load resulting in both increased internal IC power
dissipation and possible loudspeaker damage.
The headphone jack’s sleeve is not connected to circuit
ground. Using the headphone output jack as a line-level
output will place the LM4924’s bandgap 1/2VDD bias on a
plug’s sleeve connection. This presents no difficulty when
the external equipment uses capacitively coupled inputs. For
the very small minority of equipment that is DC-coupled, the
LM4924 monitors the current supplied by the amplifier that
drives the headphone jack’s sleeve. If this current exceeds
500mAPK, the amplifier is shutdown, protecting the LM4924
and the external equipment.
BYPASS CAPACITOR VALUE SELECTION
Besides minimizing the input capacitor size, careful consideration should be paid to value of CBYPASS, the capacitor
connected to the BYPASS pin. Since CBYPASS determines
how fast the LM4924 settles to quiescent operation, its value
is critical when minimizing turn-on pops. The slower the
LM4924’s outputs ramp to their quiescent DC voltage (nominally VDD/2), the smaller the turn-on pop. Choosing CB equal
to 4.7µF along with a small value of Ci (in the range of 0.1µF
to 0.47µF), produces a click-less and pop-less shutdown
function. As discussed above, choosing Ci no larger than
necessary for the desired bandwidth helps minimize clicks
and pops. This ensures that output transients are eliminated
when power is first applied or the LM4924 resumes operation after shutdown.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier. A direct consequence of the increased
power delivered to the load by a bridge amplifier is an
increase in internal power dissipation. The maximum power
dissipation for a given application can be derived from the
power dissipation graphs or from Equation 1.
PDMAX = 4(VDD)
/ (π2RL)
(1)
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 3.3V supply
the maximum power dissipation is only 138mW. Therefore,
power dissipation is not a major concern.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4924 contains circuitry that eliminates turn-on and
shutdown 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.
As the VDD/2 voltage present at the BYPASS pin ramps to its
final value, the LM4924’s internal amplifiers are configured
as unity gain buffers. An internal current source charges the
capacitor connected between the BYPASS pin and GND in a
controlled, linear manner. Ideally, the input and outputs track
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches VDD/2. As soon as the voltage on the
bypass pin is stable, the device becomes fully operational
and the amplifier outputs are reconnected to their respective
output pins. Although the BYPASS pin current cannot be
modified, changing the size of CBYPASS alters the device’s
turn-on time. There is a linear relationship between the size
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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 bypassing the supply nodes of the LM4924. A
bypass capacitor value in the range of 0.1µF to 1µF is
recommended for CS.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4924’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN
10
USING EXTERNAL POWERED SPEAKERS
The LM4924 is designed specifically for headphone operation. Often the headphone output of a device will be used to
drive external powered speakers. The LM4924 has a differential output to eliminate the output coupling capacitors. The
result is a headphone jack sleeve that is connected to VO3
instead of GND. For powered speakers that are designed to
have single-ended signals at the input, the click and pop
circuitry will not be able to eliminate the turn-on/turn-off click
and pop. Unless the inputs to the powered speakers are fully
differential the turn-on/turn-off click and pop will be very
large.
(Continued)
pin. When active, the LM4924’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 1.5V (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 SHUTDOWN pin. A
voltage that is higher than ground may increase the shutdown current.
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
SHUTDOWN pin and VDD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the
SHUTDOWN pin to ground, activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN 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
SHUTDOWN pin. Driving the SHUTDOWN pin with active
circuitry eliminates the pull-up resistor.
AUDIO POWER AMPLIFIER DESIGN
A 30mW/32Ω Audio Amplifier
Given:
Power Output
30mWrms
Load Impedance
32Ω
Input Level
1Vrms
Input Impedance
20kΩ
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be
easily found.
Since 3.3V is a standard supply voltage in most applications,
it is chosen for the supply rail in this example. Extra supply
voltage creates headroom that allows the LM4924 to reproduce peaks in excess of 30mW without producing audible
distortion. At this time, the designer must make sure that the
power supply choice along with the output impedance does
no 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 2.
SELECTING EXTERNAL COMPONENTS
Selecting proper external components in applications using
integrated power amplifiers is critical to optimize device and
system performance. While the LM4924 is tolerant of external component combinations, consideration to component
values must be used to maximize overall system quality.
The LM4924 is unity-gain stable which gives the designer
maximum system flexibility. The LM4924 should be used in
low gain configurations to minimize THD+N values, and
maximize the 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. Very large values
should not be used for the gain-setting resistors. Values for
Ri and Rf should be less than 1MΩ. Please refer to the
section, Audio Power Amplifier Design, for a more complete explanation of proper gain selection
Besides gain, one of the major considerations is the closedloop bandwidth of the amplifier. The input coupling capacitor,
Ci, forms a first order high pass filter which limits low frequency response. This value should be chosen based on
needed frequency response and turn-on time.
(2)
From Equation 2, the minimum AV is 0.98; use AV = 1. Since
the desired input impedance is 20kΩ, and with AV equal to 1,
a ratio of 1:1 results from Equation 1 for Rf to Ri. The values
are chosen with Ri = 20kΩ and Rf = 20kΩ.
SELECTION OF INPUT CAPACITOR SIZE
Amplifiying the lowest audio frequencies requires a high
value input coupling capacitor, Ci. 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 little ability to reproduce
signals below 60Hz. Applications using headphones with this
limited frequency response reap little improvement by using
a high value input capacitor.
In addition to system cost and size, turn-on time is affected
by the size of the input coupling capacitor Ci. A larger input
coupling capacitor requires more charge to reach its quiescent DC voltage. This charge comes from the output via the
feedback Thus, by minimizing the capacitor size based on
necessary low frequency response, turn-on time can be
minimized. A small value of Ci (in the range of 0.1µF to
0.39µF), is recommended.
The last step in this design example is setting the amplifier’s
−3dB frequency bandwidth. To achieve the desired ± 0.25dB
pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the ± 0.25dB
desired limit. The results are an
fL = 100Hz/5 = 20Hz
(3)
fH = 20kHz x 5 = 100kHz
(4)
and an
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LM4924
Application Information
LM4924
Application Information
1/(2π*20kΩ*20Hz) = 0.397µF
Use a 0.39µF capacitor, the closest standard value.
(Continued)
As mentioned in the Selecting Proper External Components section, Ri and Ci create a highpass filter that sets the
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (3).
Ci ≥ 1/(2πR ifL)
The high frequency pole is determined by the product of the
desired frequency pole, fH, and the differential gain, AV. With
an AV = 1 and fH = 100kHz, the resulting GBWP = 100kHz
which is much smaller than the LM4924 GBWP of 11MHz.
This figure displays that if a designer has a need to design
an amplifier with higher differential gain, the LM4924 can still
be used without running into bandwidth limitations.
(5)
The result is
HIGHER GAIN AUDIO AMPLIFIER
20121029
FIGURE 3.
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ates a low pass filter that eliminates possible high frequency
oscillations. Care should be taken when calculating the -3dB
frequency in that an incorrect combination of Rf and Cf will
cause frequency response roll off before 20kHz. A typical
combination of feedback resistor and capacitor that will not
produce audio band high frequency roll off is Rf = 20kΩ and
Cf = 25pF. These components result in a -3dB point of
approximately 320kHz.
(Continued)
The LM4924 is unity-gain stable and requires no external
components besides gain-setting resistors, input coupling
capacitors, and proper supply bypassing in the typical application. However, if a very large closed-loop differential gain
is required, a feedback capacitor (Cf) may be needed to
bandwidth limit the amplifier. This feedback capacitor creREFERENCE DESIGN BOARD and LAYOUT GUIDELINES
MSOP & SD BOARDS
20121030
FIGURE 4.
(Note: RPU2 is not required. It is used for test measurement purposes only.)
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LM4924
Application Information
LM4924
Application Information
daisy chaining traces together in a serial manner) can
greatly enhance low level signal performance. Star trace
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.
(Continued)
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.
Single-Point Power / 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.
Minimization of THD
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 LM4924 in a given application.
Placement of Digital and Analog Components
All digital components and high-speed digital signal traces
should be located as far away as possible from analog
components and circuit traces.
GENERAL MIXED SIGNAL LAYOUT
RECOMMENDATION
Avoiding Typical Design / Layout Problems
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
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.
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LM4924
Physical Dimensions
inches (millimeters) unless otherwise noted
MSOP Package
Order Number LM4924MM
NS Package Number MUB10A
SD Package
Order Number LM4924SD
NS Package Number SDA10A
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LM4924 2 Cell Battery, 40mW Per Channel Output Capacitor-Less (OCL) Stereo Headphone Audio
Amplifier
Notes
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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National Semiconductor
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Fax: 81-3-5639-7507
Email: [email protected]
Tel: 81-3-5639-7560