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 8
trans-
ducer loads at a continuous average output of 400mW with
less than 2%THD+N.
The LM4665 has high efficiency with an 8
transducer 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
j
Efficiency at 100mW into 8
transducer
75%(typ)
j
Efficiency at 400mW into 8
transducer
80%(typ)
j
Total quiescent power supply current (3V)
3mA(typ)
j
Total shutdown power supply current (3V) 0.01A(typ)
j
Single supply range (MSOP & LD)
2.7V to 5.5V
j
Single supply range (ITL) (Note 11)
2.7V to 3.8V
Features
n
No output filter required for inductive transducers
n
Selectable gain of 6dB (2V/V) or 12dB (4V/V)
n
Very fast turn on time: 5ms (typ)
n
User selectable shutdown High or Low logic level
n
Minimum external components
n
"Click and pop" suppression circuitry
n
Micro-power shutdown mode
n
Short circuit protection
n
micro SMD, LLP, and MSOP packages (no heat sink
required)
Applications
n
Mobile phones
n
PDAs
n
Portable 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
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
-65C to +150C
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
)
150C
Thermal Resistance
JA
(MSOP)
190C/W
JC
(MSOP)
56C/W
JA
(micro SMD)
180C/W
JA
(LLP) (Note 10)
63C/W
JC
(LLP) (Note 10)
12C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale
Package."
Operating Ratings
(Note 2)
Temperature Range
T
MIN
T
A
T
MAX
-40C
T
A
85C
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
= 8
+ 33H, measurement bandwidth is
<
10Hz - 22kHz unless other-
wise specified. Limits apply for T
A
= 25C.
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, 8
+ 22H Load
14
14.5
mA
mA
I
SD
Shutdown Current
V
SD
= V
SD Mode
(Note 9)
0.1
5.0
A (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
6
5.5
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
k
V
Gain Select
= GND, Gain = 12dB
65
k
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
V
LM4665
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3
Electrical Characteristics V
DD
= 3V
(Notes 1, 2)
The following specifications apply for V
DD
= 3V, and R
L
= 8
+ 33H, measurement bandwidth is
<
10Hz - 22kHz unless oth-
erwise specified. Limits apply for T
A
= 25C.
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, 8
+ 22H 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
A (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
6
5.5
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
k
V
Gain Select
= GND, Gain = 12dB
65
k
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
V
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 T
JMAX
,
JA
, and the ambient temperature T
A
. The maximum
allowable power dissipation is P
DMAX
= (T
JMAX
T
A
)/
JA
or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4665, T
JMAX
= 150C.
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 k
resistor.
Note 5: Machine Model, 220 pF240 pF discharged through all pins.
Note 6: Typical specifications are specified at 25C 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 I
SD
by a maximum of 2A. The Shutdown Mode pin
should be connected to V
DD
or GND and the Shutdown pin should be driven as close as possible to V
DD
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 8
speaker loads. The supply range may be increased as speaker
impedance is increased. It is not recommended that 4
loads 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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