LM4671
Filterless High Efficiency 2.5W Switching Audio
Amplifier
General Description
The LM4671 is a single supply, high efficiency 2.5W switch-
ing audio amplifier. A low noise, filterless PWM architecture
eliminates the output filter, reducing external component
count, board area consumption, system cost, and simplifying
design.
The LM4671 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing on a single 5V supply, it is capable of driving a 4
speaker load at a continuous average output of 2.1W with
less than 1% THD+N. Its flexible power supply requirements
allow operation from 2.4V to 5.5V.
The LM4671 has high efficiency with speaker loads com-
pared to a typical Class AB amplifier. With a 3V supply
driving an 8
speaker, the IC's efficiency for a 100mW
power level is 80%, reaching 88% at 400mW output power.
The LM4671 features a low-power consumption shutdown
mode. Shutdown may be enabled by driving the Shutdown
pin to a logic low (GND).
The gain of the LM4671 is externally configurable which
allows independent gain control from multiple sources by
summing the signals.
Key Specifications
j
Efficiency at 3.6V, 100mW into 8
speaker 80% (typ)
j
Efficiency at 3.6V, 400mW into 8
speaker 88% (typ)
j
Efficiency at 5V, 1W into 8
speakerr
86% (typ)
j
Quiescent current, 3.6V supply
2.8mA (typ)
j
Total shutdown power supply current
0.01A (typ)
j
Single supply range
2.4V to 5.5V
Features
n
No output filter required for inductive loads
n
Externally configurable gain
n
Very fast turn on time: 1ms (typ)
n
Minimum external components
n
"Click and pop" suppression circuitry
n
Micro-power shutdown mode
n
Available in space-saving microSMD package
Applications
n
Mobile phones
n
PDAs
n
Portable electronic devices
Typical Application
Boomer
is a registered trademark of National Semiconductor Corporation.
201073J3
FIGURE 1. Typical Audio Amplifier Application Circuit
March 2005
LM4671
Filterless
High
Efficiency
2.5W
Switching
Audio
Amplifier
2005 National Semiconductor Corporation
DS201073
www.national.com
Connection Diagrams
9 Bump micro SMD Package
micro SMD Marking
20107336
Top View
Order Number LM4671ITL, LM4671ITLX
See NS Package Number TLA09AAA
201073C6
Top View
X -- Date Code
T -- Die Traceability
G -- Boomer Family
E7 -- LM4671ITL
LM4671
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2
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, all other pins (Note 4)
2.0kV
ESD Susceptibility (Note 5)
200V
Junction Temperature (T
JMAX
)
150C
Thermal Resistance
JA
(micro SMD)
220C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale
Package."
Operating Ratings
(Note 1) (Note 2)
Temperature Range
T
MIN
T
A
T
MAX
-40C
T
A
85C
Supply Voltage
2.4V
V
DD
5.5V
Electrical Characteristics
(Notes 1, 2)
The following specifications apply for A
V
= 2V/V (R
I
= 150k
), R
L
= 15H + 8
+ 15H unless otherwise specified. Limits ap-
ply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4671
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
|V
OS
|
Differential Output Offset Voltage
V
I
= 0V, A
V
= 2V/V,
V
DD
= 2.4V to 5.0V
5
mV (max)
PSRR
GSM
GSM Power Supply Rejection Ratio V
DD
= 2.4V to 5.0V
61
dB (min)
CMRR
GSM
GSM Common Mode Rejection
Ratio
V
DD
= 2.4V to 5.0V
V
IC
= V
DD
/2 to 0.5V,
V
IC
= V
DD
/2 to V
DD
0.8V
68
dB (min)
|I
IH
|
Logic High Input Current
V
DD
= 5.0V, V
I
= 5.5V
17
100
A (max)
|I
IL
|
Logic Low Input Current
V
DD
= 5.0V, V
I
= 0.3V
0.9
5
A (max)
V
IN
= 0V, No Load, V
DD
= 5.0V
6.4
mA (max)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, No Load, V
DD
= 3.6V
3.8
6.2
mA
V
IN
= 0V, No Load, V
DD
=2.4V
2.0
3.0
mA (max)
I
SD
Shutdown Current
V
SHUTDOWN
= 0V
V
DD
= 2.4V to 5.0V
0.01
1
A (max)
V
SDIH
Shutdown voltage input high
1.2
1.4
V (min)
V
SDIL
Shutdown voltage input low
1.1
0.4
V (max)
R
OSD
Output Impedance
V
SHUTDOWN
= 0.4V
100
k
A
V
Gain
300k
/R
I
270k
/R
I
330k
/R
I
V/V (min)
V/V (max)
R
SD
Resistance from Shutdown Pin to
GND
300
k
P
O
Output Power
R
L
= 15H + 4
+ 15H
THD = 10% (max)
f = 1kHz, 22kHz BW
V
DD
= 5V
V
DD
= 3.6V
V
DD
= 2.5V
2.5
1.3
520
W
W
mW
R
L
= 15H + 4
+ 15H
THD = 1% (max)
f = 1kHz, 22kHz BW
V
DD
= 5V
V
DD
= 3.6V
V
DD
= 2.5V
2.21
1.06
420
W
W
mW
LM4671
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3
Electrical Characteristics
(Notes 1, 2)
The following specifications apply for A
V
= 2V/V (R
I
= 150k
), R
L
= 15H + 8
+ 15H unless otherwise specified. Limits
apply for T
A
= 25C. (Continued)
Symbol
Parameter
Conditions
LM4671
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
P
O
Output Power
R
L
= 15H + 8
+ 15H
THD = 10% (max)
f = 1kHz, 22kHz BW
V
DD
= 5V
1.7
W
V
DD
= 3.6V
870
mW
V
DD
= 2.5V
425
mW
R
L
= 15H + 8
+ 15H
THD = 1% (max)
f = 1kHz, 22kHz BW
V
DD
= 5V
1.19
W
V
DD
= 3.6V
700
600
mW
V
DD
= 2.5V
350
mW
THD+N
Total Harmonic Distortion + Noise
V
DD
= 5V, P
O
= 0.1W
RMS
,
f = 1kHz
0.09
%
V
DD
= 3.6V, P
O
= 0.1W
RMS
,
f = 1kHz
0.04
%
V
DD
= 3.6V, P
O
= 0.1W
RMS
,
f = 5kHz
0.12
%
V
DD
= 3.6V, P
O
= 0.1W
RMS
,
f = 10kHz
0.05
%
V
DD
= 3.6V, 5V
V
Ripple
= 200mV
PP
Sine,
f
Ripple
= 217Hz
Inputs to AC GND, C
I
= 2F
61.8
dB
PSRR
Power Supply Rejection Ratio
V
DD
= 3.6V, 5V
V
Ripple
= 200mV
PP
Sine,
f
Ripple
= 1kHz
Inputs to AC GND, C
I
= 2F
59.8
dB
V
DD
= 3.6V, 5V
V
Ripple
= 200mV
PP
Sine,
f
Ripple
= 10kHz
Inputs to AC GND, C
I
= 2F
48.7
dB
V
DD
= 3.6V, 5V
V
Ripple
= 200mV
PP
Sine,
f
Ripple
= 217Hz
f
IN
= 1kHz, P
O
= 10mW
RMS
65.7
dB
SNR
Signal to Noise Ratio
V
DD
= 5V, P
O
= 1W
RMS
93
dB
e
OUT
Output Noise
V
DD
= 3.6V, f = 20Hz 20kHz
Inputs to AC GND, C
I
= 2F
No Weighting
58
V
RMS
V
DD
= 3.6V, Inputs to AC GND
C
I
= 2F, A Weighted
38
V
RMS
CMRR
Common Mode Rejection Ratio
V
DD
= 3.6V, V
Ripple
= 1V
PP
Sine
f
Ripple
= 217Hz
68.3
dB
T
WU
Wake-up Time
V
DD
= 3.6V
17
s
T
SD
Shutdown Time
140
s
LM4671
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4
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 LM4671, T
JMAX
= 150C.
The typical
JA
is 220C/W for the microSMD package.
Note 4: Human body model, 100pF discharged through a 1.5k
resistor.
Note 5: Machine Model, 220pF240pF 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 pin should
be driven as close as possible to GND for minimal shutdown current and to V
DD
for the best THD performance in PLAY mode. See the Application Information
section under SHUTDOWN FUNCTION for more information.
Note 10: The performance graphs were taken using the Audio Precision AUX-0025 Switching Amplifier measurement Filter in series with the LC filter on the demo
board.
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.
2.
C
I
Input AC coupling capacitor which blocks the DC voltage at the amplifier's input terminals.
LM4671
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