LM4665
LM4665 Filterless High Efficiency 1W Switching Audio Amplifier
Literature Number: SNAS146D
LM4665
Filterless High Efficiency 1W Switching Audio Amplifier
General Description
The LM4665 is a fully integrated single-supply high efficiency
switching audio amplifier. It features an innovative modulator
that eliminates the LC output filter used with typical switching
amplifiers. Eliminating the output filter reduces parts count,
simplifies circuit design, and reduces board area. The
LM4665 processes analog inputs with a delta-sigma modu-
lation technique that lowers output noise and THD when
compared to conventional pulse width modulators.
The LM4665 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing on a single 3V supply, it is capable of driving 8Ωtrans-
ducer loads at a continuous average output of 400mW with
less than 2%THD+N.
The LM4665 has high efficiency with an 8Ωtransducer load
compared to a typical Class AB amplifier. With a 3V supply,
the IC’s efficiency for a 100mW power level is 75%, reaching
80% at 400mW output power.
The LM4665 features a low-power consumption shutdown
mode. Shutdown may be enabled by either a logic high or
low depending on the mode selection. Connecting the Shut-
down Mode pin to either V
DD
(high) or GND (low) enables
the Shutdown pin to be driven in a likewise manner to
activate shutdown.
The LM4665 has fixed selectable gain of either 6dB or 12dB.
The LM4665 has short circuit protection against a short from
the outputs to V
DD
, GND or across the outputs.
Key Specifications
jEfficiency at 100mW into 8Ωtransducer 75%(typ)
jEfficiency at 400mW into 8Ωtransducer 80%(typ)
jTotal quiescent power supply current (3V) 3mA(typ)
jTotal shutdown power supply current (3V) 0.01µA(typ)
jSingle supply range (MSOP & LD) 2.7V to 5.5V
jSingle supply range (ITL) (Note 11) 2.7V to 3.8V
Features
nNo output filter required for inductive transducers
nSelectable gain of 6dB (2V/V) or 12dB (4V/V)
nVery fast turn on time: 5ms (typ)
nUser selectable shutdown High or Low logic level
nMinimum external components
n"Click and pop" suppression circuitry
nMicro-power shutdown mode
nShort circuit protection
nmicro SMD, LLP, and MSOP packages (no heat sink
required)
Applications
nMobile phones
nPDAs
nPortable electronic devices
Typical Application
Boomer®is a registered trademark of National Semiconductor Corporation.
20027001
FIGURE 1. Typical Audio Amplifier Application Circuit
December 2002
LM4665 Filterless High Efficiency 1W Switching Audio Amplifier
© 2002 National Semiconductor Corporation DS200270 www.national.com
Connection Diagrams
Mini Small Outline (MSOP) Package 9 Bump micro SMD Package
20027023
Top View
Order Number LM4665MM
See NS Package Number MUB10A
20027036
Top View
Order Number LM4665ITL, LM4665ITLX
See NS Package Number TLA09AAA
LLP Package MSOP Marking
200270D0
Top View
Order Number LM4665LD
See NS Package Number LDA10B
200270C5
Top View
G - Boomer Family
C5 - LM4665MM
micro SMD Marking
200270C6
Top View
X - Date Code
T- Die Traceability
G - Boomer Family
A2 - LM4665ITL
200270C9
Top View
Z - Plant Code
XY - Date Code
TT- Die Traceability
Bottom Line-Part Number
LM4665
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Absolute Maximum Ratings (Notes 1,
2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (Note 1) 6.0V
Storage Temperature −65˚C to +150˚C
Voltage at Any Input Pin V
DD
+ 0.3V ≥V≥GND - 0.3V
Power Dissipation (Note 3) Internally Limited
ESD Susceptibility (Note 4) 2.0kV
ESD Susceptibility (Note 5) 200V
Junction Temperature (T
J
) 150˚C
Thermal Resistance
θ
JA
(MSOP) 190˚C/W
θ
JC
(MSOP) 56˚C/W
θ
JA
(micro SMD) 180˚C/W
θ
JA
(LLP) (Note 10) 63˚C/W
θ
JC
(LLP) (Note 10) 12˚C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale
Package."
Operating Ratings (Note 2)
Temperature Range
T
MIN
≤T
A
≤T
MAX
−40˚C ≤T
A
≤85˚C
Supply Voltage (MSOP & LD) 2.7V ≤V
DD
≤5.5V
Supply Voltage (ITL) (Note11) 2.7V ≤V
DD
≤3.8V
Electrical Characteristics V
DD
=5V (Notes 1, 2, 11)
The following specifications apply for V
DD
= 5V, R
L
=8Ω+ 33µH, measurement bandwidth is <10Hz - 22kHz unless other-
wise specified. Limits apply for T
A
= 25˚C.
Symbol Parameter Conditions
LM4665 Units
(Limits)
Typical Limit
(Note 6) (Notes 7, 8)
I
DD
Quiescent Power Supply Current V
IN
= 0V, No Load
V
IN
= 0V, 8Ω+ 22µH Load
14
14.5
mA
mA
I
SD
Shutdown Current V
SD
=V
SD Mode
(Note 9) 0.1 5.0 µA (max)
V
SDIH
Shutdown Voltage Input High V
SD Mode
=V
DD
1.2 1.4 V (min)
V
SDIL
Shutdown Voltage Input Low V
SD Mode
=V
DD
1.1 0.4 V (max)
V
SDIH
Shutdown Voltage Input High V
SD Mode
= GND 1.2 1.4 V (min)
V
SDIL
Shutdown Voltage Input Low V
SD Mode
= GND 1.1 0.4 V (max)
V
GSIH
Gain Select Input High 1.2 1.4 V (min)
V
GSIL
Gain Select Input Low 1.1 0.4 V (max)
A
V
Closed Loop Gain V
Gain Select
=V
DD
65.5
6.5
dB (min)
dB (max)
A
V
Closed Loop Gain V
Gain Select
= GND 12 11.5
12.5
dB (min)
dB (max)
V
OS
Output Offset Voltage 10 mV
T
WU
Wake-up Time 5 ms
P
o
Output Power THD+N = 3% (max), f
IN
= 1kHz 1.4 W
THD+N Total Harmonic Distortion+Noise P
O
= 400mW
RMS
,f
IN
= 1kHz 0.8 %
R
IN
Differential Input Resistance V
Gain Select
=V
DD
, Gain = 6dB 100 kΩ
V
Gain Select
= GND, Gain = 12dB 65 kΩ
PSRR Power Supply Rejection Ratio V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz, A
V
= 6dB
Inputs Terminated
52 dB
CMRR Common Mode Rejection Ratio V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz, A
V
= 6dB 43 dB
e
N
Output Noise Voltage A-Weighted filter, V
IN
= 0V 350 µV
LM4665
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Electrical Characteristics V
DD
=3V (Notes 1, 2)
The following specifications apply for V
DD
= 3V, and R
L
=8Ω+ 33µH, measurement bandwidth is <10Hz - 22kHz unless oth-
erwise specified. Limits apply for T
A
= 25˚C.
Symbol Parameter Conditions
LM4665 Units
(Limits)
Typical Limit
(Note 6) (Notes 7, 8)
I
DD
Quiescent Power Supply Current V
IN
= 0V, No Load
V
IN
= 0V, 8Ω+ 22µH Load
3.0
3.5
7.0 mA (max)
mA
I
SD
Shutdown Current V
SD
=V
SD Mode
(Note 9) 0.01 5.0 µA (max)
V
SDIH
Shutdown Voltage Input High V
SD Mode
=V
DD
1.0 1.4 V (min)
V
SDIL
Shutdown Voltage Input Low V
SD Mode
=V
DD
0.8 0.4 V (max)
V
SDIH
Shutdown Voltage Input High V
SD Mode
= GND 1.0 1.4 V (min)
V
SDIL
Shutdown Voltage Input Low V
SD Mode
= GND 0.8 0.4 V (max)
V
GSIH
Gain Select Input High 1.0 1.4 V (min)
V
GSIL
Gain Select Input Low 0.8 0.4 V (max)
A
V
Closed Loop Gain V
Gain Select
=V
DD
65.5
6.5
dB (min)
dB (max)
A
V
Closed Loop Gain V
Gain Select
= GND 12 11.5
12.5
dB (min)
dB (max)
V
OS
Output Offset Voltage 10 mV
T
WU
Wake-up Time 5 ms
P
o
Output Power THD+N = 2% (max), f
IN
= 1kHz 400 350 mW (min)
THD+N Total Harmonic Distortion+Noise P
O
= 100mW
RMS
,f
IN
= 1kHz 0.4 % (max)
R
IN
Differential Input Resistance V
Gain Select
=V
DD
, Gain = 6dB 100 kΩ
V
Gain Select
= GND, Gain = 12dB 65 kΩ
PSRR Power Supply Rejection Ratio
V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz, A
V
= 6dB,
Inputs Terminated
52 dB
CMRR Common Mode Rejection Ratio V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz, A
V
= 6dB 39 dB
e
N
Output Noise Voltage A-Weighted filter, V
IN
= 0V 350 µV
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: 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–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4665, TJMAX = 150˚C.
See the Efficiency and Power Dissipation versus Output Power curves for more information.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩresistor.
Note 5: Machine Model, 220 pF–240 pF discharged through all pins.
Note 6: Typical specifications are specified at 25˚C and represent the parametric norm.
Note 7: Tested 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.
Note 9: Shutdown current is measured in a normal room environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. The Shutdown Mode pin
should be connected to VDD or GND and the Shutdown pin should be driven as close as possible to VDD or GND for minimum shutdown current and the best THD
performance in PLAY mode. See the Application Information section under SHUTDOWN FUNCTION for more information.
Note 10: The exposed-DAP of the LDA10B package should be electrically connected to GND.
Note 11: The LM4665 in the micro SMD package (ITL) has an operating range of 2.7V - 3.8V for 8Ωspeaker loads. The supply range may be increased as speaker
impedance is increased. It is not recommended that 4Ωloads be used with the micro SMD package. To increase the supply voltage operating range, see Figure 2
and INCREASING SUPPLY VOLTAGE RANGE in the Application Information section for more information.
External Components Description
(Figure 1)
Components Functional Description
1. C
S
Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing
section for information concerning proper placement and selection of the supply bypass capacitor.
LM4665
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Typical Performance Characteristics
THD+N vs Frequency
V
DD
= 5V, R
L
=8Ω+ 33µH
P
OUT
= 400mW, 30kHz BW
THD+N vs Frequency
V
DD
= 3V, R
L
=8Ω+ 33µH
P
OUT
= 100mW, 30kHz BW
200270E0 200270D9
THD+N vs Frequency
V
DD
= 3.3V, R
L
=4Ω+ 33µH
P
OUT
= 300mW, 30kHz BW
THD+N vs Power Out
V
DD
= 5V, R
L
=8Ω+ 33µH
f = 1kHz, 22kHz BW
200270D8 200270D5
THD+N vs Power Out
V
DD
= 3V, R
L
=8Ω+ 33µH
f = 1kHz, 22kHz BW
THD+N vs Power Out
V
DD
= 3.3V, R
L
=4Ω+ 33µH
f = 1kHz, 22kHz BW
200270E2 200270E1
LM4665
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Typical Performance Characteristics (Continued)
THD+N vs Common-Mode Voltage
V
DD
= 5V, R
L
=8Ω+ 33µH, f = 1kHz
P
OUT
= 400mW, 22kHz BW
THD+N vs Common-Mode Voltage
V
DD
= 3V, R
L
=8Ω+ 33µH, f = 1kHz
P
OUT
= 100mW, 22kHz BW
20027032
20027031
CMRR vs Frequency
V
DD
= 5V, R
L
=8Ω+ 33µH
V
CM
= 100mV
RMS
Sine Wave, 80kHz BW
CMRR vs Frequency
V
DD
= 3V, R
L
=8Ω+ 33µH
V
CM
= 100mV
RMS
Sine Wave, 80kHz BW
20027095 20027098
PSRR vs DC Common-Mode Voltage
V
DD
= 5V, R
L
=8Ω+ 33µH
V
Ripple
= 100mV
RMS
,f
Ripple
= 217Hz Sine Wave
PSRR vs DC Common-Mode Voltage
V
DD
= 3V, R
L
=8Ω+ 33µH
V
Ripple
= 100mV
RMS
,f
Ripple
= 217Hz Sine Wave
20027097
20027096
LM4665
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Typical Performance Characteristics (Continued)
PSRR vs Frequency
V
DD
= 5V, R
L
=8Ω+ 33µH
V
CM
= 100mV
RMS
Sine Wave, 22kHz BW
PSRR vs Frequency
V
DD
= 3V, R
L
=8Ω+ 33µH
V
CM
= 100mV
RMS
Sine Wave, 22kHz BW
20027099 20027094
Efficiency (top trace) and
Power Dissipation (bottom trace) vs Output Power
V
DD
= 5V, R
L
=8Ω+ 33µH, f = 1kHz, THD <3%
Efficiency (top trace) and
Power Dissipation (bottom trace) vs Output Power
V
DD
= 3V, R
L
=8Ω+ 33µH, f = 1kHz, THD <2%
200270A2
200270A1
Efficiency (top trace) and
Power Dissipation (bottom trace) vs Output Power
V
DD
= 3.3V, R
L
=4Ω+ 33µH, f = 1kHz, THD <2%
Gain Threshold Voltages
V
DD
=3V-5V
200270A5
200270A3
LM4665
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Typical Performance Characteristics (Continued)
Output Power vs Supply Voltage
R
L
=16Ω+ 33µH, f = 1kHz
Output Power vs Supply Voltage
R
L
=8Ω+ 33µH, f = 1kHz
200270E3 200270D7
Output Power vs Supply Voltage
R
L
=4Ω+ 33µH, f = 1kHz
Shutdown Hysteresis Voltage
V
DD
= 5V, SD Mode = GND (SD Low)
200270D6
200270A7
Shutdown Hysteresis Voltage
V
DD
= 3V, SD Mode = GND (SD Low)
Shutdown Hysteresis Voltage
V
DD
= 5V, SD Mode = GND (SD High)
200270A8 200270A9
LM4665
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Typical Performance Characteristics (Continued)
Shutdown Hysteresis Voltage
V
DD
= 3V, SD Mode = GND (SD High)
Supply Current
vs Supply Voltage
R
L
=8Ω+ 33µH
200270B0
20027002
Application Information
GENERAL AMPLIFIER FUNCTION
The output signals generated by the LM4665 consist of two,
BTL connected, output signals that pulse momentarily from
near ground potential to V
DD
. The two outputs can pulse
independently with the exception that they both may never
pulse simultaneously as this would result in zero volts across
the BTL load. The minimum width of each pulse is approxi-
mately 160ns. However, pulses on the same output can
occur sequentially, in which case they are concatenated and
appear as a single wider pulse to achieve an effective 100%
duty cycle. This results in maximum audio output power for a
given supply voltage and load impedance. The LM4665 can
achieve much higher efficiencies than class AB amplifiers
while maintaining acceptable THD performance.
The short (160ns) drive pulses emitted at the LM4665 out-
puts means that good efficiency can be obtained with mini-
mal load inductance. The typical transducer load on an audio
amplifier is quite reactive (inductive). For this reason, the
load can act as it’s own filter, so to speak. This "filter-less"
switching amplifier/transducer load combination is much
more attractive economically due to savings in board space
and external component cost by eliminating the need for a
filter.
POWER DISSIPATION AND EFFICIENCY
In general terms, efficiency is considered to be the ratio of
useful work output divided by the total energy required to
produce it with the difference being the power dissipated,
typically, in the IC. The key here is “useful” work. For audio
systems, the energy delivered in the audible bands is con-
sidered useful including the distortion products of the input
signal. Sub-sonic (DC) and super-sonic components
(>22kHz) are not useful. The difference between the power
flowing from the power supply and the audio band power
being transduced is dissipated in the LM4665 and in the
transducer load. The amount of power dissipation in the
LM4665 is very low. This is because the ON resistance of the
switches used to form the output waveforms is typically less
than 0.25Ω. This leaves only the transducer load as a po-
tential "sink" for the small excess of input power over audio
band output power. The LM4665 dissipates only a fraction of
the excess power requiring no additional PCB area or cop-
per plane to act as a heat sink.
DIFFERENTIAL AMPLIFIER EXPLANATION
As logic supply voltages continue to shrink, designers are
increasingly turning to differential analog signal handling to
preserve signal to noise ratios with restricted voltage swing.
The LM4665 is a fully differential amplifier that features
differential input and output stages. A differential amplifier
amplifies the difference between the two input signals. Tra-
ditional audio power amplifiers have typically offered only
single-ended inputs resulting in a 6dB reduction in signal to
noise ratio relative to differential inputs. The LM4665 also
offers the possibility of DC input coupling which eliminates
the two external AC coupling, DC blocking capacitors. The
LM4665 can be used, however, as a single ended input
amplifier while still retaining it’s fully differential benefits. In
fact, completely unrelated signals may be placed on the
input pins. The LM4665 simply amplifies the difference be-
tween the signals. A major benefit of a differential amplifier is
the improved common mode rejection ratio (CMRR) over
single input amplifiers. The common-mode rejection charac-
teristic of the differential amplifier reduces sensitivity to
ground offset related noise injection, especially important in
high noise applications.
PCB LAYOUT CONSIDERATIONS
As output power increases, interconnect resistance (PCB
traces and wires) between the amplifier, load and power
supply create a voltage drop. The voltage loss on the traces
between the LM4665 and the load results is lower output
power and decreased efficiency. Higher trace resistance
between the supply and the LM4665 has the same effect as
a poorly regulated supply, increase ripple on the supply line
also reducing the peak output power. The effects of residual
trace resistance increases as output current increases due
to higher output power, decreased load impedance or both.
To maintain the highest output voltage swing and corre-
sponding peak output power, the PCB traces that connect
LM4665
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Application Information (Continued)
the output pins to the load and the supply pins to the power
supply should be as wide as possible to minimize trace
resistance.
The rising and falling edges are necessarily short in relation
to the minimum pulse width (160ns), having approximately
2ns rise and fall times, typical, depending on parasitic output
capacitance. The inductive nature of the transducer load can
also result in overshoot on one or both edges, clamped by
the parasitic diodes to GND and V
DD
in each case. From an
EMI standpoint, this is an aggressive waveform that can
radiate or conduct to other components in the system and
cause interference. It is essential to keep the power and
output traces short and well shielded if possible. Use of
ground planes, beads, and micro-strip layout techniques are
all useful in preventing unwanted interference.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor (C
S
) location should be
as close as possible to the LM4665. Typical applications
employ a voltage regulator with a 10µF and a 0.1µF bypass
capacitors that increase supply stability. These capacitors do
not eliminate the need for bypassing on the supply pin of the
LM4665. A 1µF tantalum capacitor is recommended.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4665 contains shutdown circuitry that reduces current
draw to less than 0.01µA. In addition, the LM4665 contains a
Shutdown Mode pin allowing the designer to designate
whether the shutdown circuitry is activated by either a High
level logic signal or a Low level logic signal. The Shutdown
Mode pin should be permanently connected to either GND
(Low) or V
DD
(High). The LM4665 may then be placed into
shutdown by toggling the Shutdown pin to the same state as
the Shutdown Mode pin. For simplicity’s sake, this is called
"Shutdown same", as the LM4665 enters into a shutdown
state whenever the two pins are in the same logic state. The
trigger point for either shutdown high or shutdown low is
shown as a typical value in the Electrical Characteristics
Tables and in the Shutdown Hysteresis Voltage graphs
found in the Typical Performance Characteristics section.
It is best to switch between ground and supply for minimum
current usage while in the shutdown state. While the
LM4665 may be disabled with shutdown voltages in between
ground and supply, the idle current will be greater than the
typical 0.01µA value. Increased THD may also be observed
with voltages greater than GND and less than V
DD
on the
Shutdown pin when in PLAY mode.
The LM4665 has an internal resistor connected between the
Shutdown Mode and Shutdown pins. The purpose of this
resistor is to eliminate any unwanted state changes when
the Shutdown pin is floating, as long as the Shutdown Mode
pin is connected to GND or V
DD
. When the Shutdown Mode
pin is properly connected, the LM4665 will enter the shut-
down state when the Shutdown pin is left floating or if not
floating, when the shutdown voltage has crossed the corre-
sponding threshold for the logic level assigned by the Shut-
down Mode pin voltage. To minimize the supply current while
in the shutdown state, the Shutdown pin should be driven to
the same potential as the Shutdown Mode pin or left floating.
The amount of additional current due to the internal shut-
down resistor can be found by Equation (1) below.
(V
SD MODE
-V
SD
) / 60kΩ(1)
With only a 0.5V difference between the Shutdown Mode
voltage and the Shutdown voltage an additional 8.3µA of
current will be drawn while in the shutdown state.
GAIN SELECTION FUNCTION
The LM4665 has fixed selectable gain to minimize external
components, increase flexibility and simplify design. For a
differential gain of 6dB (2V/V), the Gain Select pin should be
permanently connected to V
DD
or driven to a logic high level.
For a differential gain of 12dB (4V/V), the Gain Select pin
should be permanently connected to GND or driven to a
logic low level. The gain of the LM4665 can be switched
while the amplifier is in PLAY mode driving a load with a
signal without damage to the IC. The voltage on the Gain
Select pin should be switched quickly between GND (logic
low) and V
DD
(logic high) to eliminate any possible audible
artifacts from appearing at the output. For typical threshold
voltages for the Gain Select function, refer to the Gain
Threshold Voltages graph in the Typical Performance
Characteristics section.
INCREASING SUPPLY VOLTAGE RANGE
When using the micro SMD package (ITL), the operating
supply voltage range is 2.7V - 3.8V with an 8Ωspeaker load.
To increase the operating supply voltage range, four Schot-
tky diodes (D
1
-D
4
) can be used to control the over and
undershoot of the output pulse waveform (See Figure 2
below). To reduce THD+N, small value capacitors in the
range of 10pF - 33pF (C
N1
&C
N2
) can also be added as
needed. The diodes should be placed as close to the micro
SMD package as possible.
LM4665
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Application Information (Continued)
SINGLE-ENDED CIRCUIT CONFIGURATIONS
200270E5
FIGURE 2. Increased Supply Voltage Operating Range for the micro SMD package
200270C4
FIGURE 3. Single-Ended Input, Shutdown High and Gain of 6dB Configuration
LM4665
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Application Information (Continued)
200270C2
FIGURE 4. Single-Ended Input, Shutdown High and Gain of 12dB Configuration
200270C3
FIGURE 5. Single-Ended Input, Shutdown Low and Gain of 6dB Configuration
LM4665
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Application Information (Continued)
REFERENCE DESIGN BOARD SCHEMATIC
200270C1
FIGURE 6. Single-Ended Input, Shutdown Low and Gain of 12dB Configuration
200270B1
FIGURE 7.
LM4665
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Application Information (Continued)
In addition to the minimal parts required for the application
circuit, a measurement filter is provided on the evaluation
circuit board so that conventional audio measurements can
be conveniently made without additional equipment. This is a
balanced input / grounded differential output low pass filter
with a 3dB frequency of approximately 35kHz and an on
board termination resistor of 300Ω(see schematic). Note
that the capacitive load elements are returned to ground.
This is not optimal for common mode rejection purposes, but
due to the independent pulse format at each output there is
a significant amount of high frequency common mode com-
ponent on the outputs. The grounded capacitive filter ele-
ments attenuate this component at the board to reduce the
high frequency CMRR requirement placed on the analysis
instruments.
Even with the grounded filter the audio signal is still differ-
ential, necessitating a differential input on any analysis in-
strument connected to it. Most lab instruments that feature
BNC connectors on their inputs are NOT differential re-
sponding because the ring of the BNC is usually grounded.
The commonly used Audio Precision analyzer is differential,
but its ability to accurately reject fast pulses of 160nS width
is questionable necessitating the on board measurement
filter. When in doubt or when the signal needs to be single-
ended, use an audio signal transformer to convert the differ-
ential output to a single ended output. Depending on the
audio transformer’s characteristics, there may be some at-
tenuation of the audio signal which needs to be taken into
account for correct measurement of performance.
Measurements made at the output of the measurement filter
suffer attenuation relative to the primary, unfiltered outputs
even at audio frequencies. This is due to the resistance of
the inductors interacting with the termination resistor (300Ω)
and is typically about -0.35dB (4%). In other words, the
voltage levels (and corresponding power levels) indicated
through the measurement filter are slightly lower than those
that actually occur at the load placed on the unfiltered out-
puts. This small loss in the filter for measurement gives a
lower output power reading than what is really occurring on
the unfiltered outputs and its load.
LM4665 MSOP BOARD ARTWORK
Composite View Silk Screen
200270B2 200270B3
Top Layer Bottom Layer
200270B4 200270B5
LM4665
www.national.com 14
Application Information (Continued)
LM4665 LLP BOARD ARTWORK
Composite View Silk Screen
200270D1 200270D2
Top Layer Bottom Layer
200270D3 200270D4
LM4665
www.national.com15
Application Information (Continued)
LM4665 micro SMD BOARD ARTWORK
Composite View Silk Screen
200270C7 200270C8
Top Layer Bottom Layer
200270B9 200270C0
LM4665
www.national.com 16
Physical Dimensions inches (millimeters) unless otherwise noted
9 Bump micro SMD
Order Number LM4665ITL, LM4665ITLX
NS Package Number TLA09AAA
X
1
= 1.514 X
2
= 1.514 X
3
= 0.600
Mini Small Outline (MSOP)
Order Number LM4665MM
NSPackage Number MUB10A
LM4665
www.national.com17
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
LLP
Order Number LM4665LD
NSPackage Number LDA10B
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.
National Semiconductor
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
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Support Center
Fax: 65-6250 4466
Email: ap.support@nsc.com
Tel: 65-6254 4466
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Japan Customer Support Center
Fax: 81-3-5639-7507
Email: nsj.crc@jksmtp.nsc.com
Tel: 81-3-5639-7560
www.national.com
LM4665 Filterless High Efficiency 1W Switching Audio Amplifier
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.
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