LM4664
Filterless High Efficiency 1.1W Switching Audio
Amplifier
General Description
The LM4664 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
LM4664 processes analog inputs with a delta-sigma modu-
lation technique that lowers output noise and THD when
compared to conventional pulse width modulators.
The LM4664 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 425mW with
less than 1%THD+N. Its flexible power supply requirements
allow operation from 2.7V to 5.5V.
The LM4664 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 74%, reaching
84% at 425mW output power.
The LM4664 features a low-power consumption shutdown
mode. Shutdown may be enabled by driving the Shutdown
pin to a logic low (GND).
The LM4664 has fixed selectable gain of either 6dB or 12dB.
The LM4664 has short circuit protection against a short from
the outputs to V
DD
, GND, or across the outputs.
Key Specifications
j
Efficiency at 3V, 100mW into 8
transducer 74% (typ)
j
Efficiency at 3V, 425mW into 8
transducer 84% (typ)
j
Efficiency at 5V, 1W into 8
transducer
86% (typ)
j
Total quiescent power supply current
3.5mA (typ)
j
Total shutdown power supply current
0.4A (typ)
j
Single supply range
2.7V to 5.5V
Features
n
No output filter required for inductive transducers
n
Selectable gain of 6dB or 12dB
n
Very fast turn on time: 7ms (typ)
n
Minimum external components
n
"Click and pop" suppression circuitry
n
Micro-power shutdown mode
n
Short circuit protection
n
Available in space-saving micro SMD package
Applications
n
Mobile phones
n
PDAs
n
Portable electronic devices
Typical Application
Boomer
is a registered trademark of National Semiconductor Corporation.
200960G5
FIGURE 1. Typical Audio Amplifier Application Circuit
March 2004
LM4664
Filterless
High
Efficiency
1.1W
Switching
Audio
Amplifier
2004 National Semiconductor Corporation
DS200960
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 (Note1)
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)
7.0kV
ESD Susceptibility (Note 5)
250V
Junction Temperature (T
J
)
150C
Thermal Resistance
JA
(micro SMD)
220C/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
2.7V
V
DD
5.5V
Electrical Characteristics V
DD
= 3V
(Notes 1, 2)
The following specifications apply for V
DD
= 3V and R
L
= 15H + 8
+ 15H unless otherwise specified. Limits apply for T
A
=
25C.
Symbol
Parameter
Conditions
LM4664
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, No Load
V
IN
= 0V, R
L
= 15H + 8
+ 15H
3.50
3.75
5.0
mA
mA (max)
I
SD
Shutdown Current
V
SD
= GND (Note 9)
0.4
2.0
A (max)
V
SDIH
Shutdown Voltage Input High
1.0
1.4
V (min)
V
SDIL
Shutdown Voltage Input Low
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
dB
A
V
Closed Loop Gain
V
Gain Select
= GND
12
dB
V
OS
Output Offset Voltage
10
25
mV (max)
T
WU
Wake-up Time
7
ms
P
o
Output Power
THD = 1% (max), f = 1kHz
425
mW
THD+N
Total Harmonic Distortion+Noise
P
O
= 100mW
RMS
; f
IN
= 1kHz
0.35
%
R
IN
Differential Input Resistance
V
Gain Select
= V
DD
90
k
V
Gain Select
= GND
60
k
PSRR
Power Supply Rejection Ratio
V
Ripple
= 100mV
RMS
sine wave
Inputs terminated to GND
56
(f = 217Hz)
dB
V
Ripple
= 100mV
RMS
sine wave
P
OUT
= 10mW,1kHz
65
(f = 217Hz)
dB
CMRR
Common Mode Rejection Ratio
V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz
41
dB
SNR
Signal to Noise Ratio
P
O
= 400mW
RMS
; A-Weighted Filter
83
dB
e
OUT
Output Noise
A-Weighted filter, V
in
= 0V
125
V
LM4664
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3
Electrical Characteristics V
DD
= 5V
(Notes 1, 2)
The following specifications apply for V
DD
= 5V and R
L
= 15H + 8
+ 15H unless otherwise specified. Limits apply for T
A
=
25C.
Symbol
Parameter
Conditions
LM4664
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, No Load
V
IN
= 0V, R
L
= 15H + 8
+ 15H
8
9
mA
mA
I
SD
Shutdown Current
V
SD
= GND (Note 9)
0.4
A
V
SDIH
Shutdown Voltage Input High
1.2
V
V
SDIL
Shutdown Voltage Input Low
1.1
V
V
GSIH
Gain Select Input High
1.2
V
V
GSIL
Gain Select Input Low
1.1
V
A
V
Closed Loop Gain
V
Gain Select
= V
DD
6
dB
A
V
Closed Loop Gain
V
Gain Select
= GND
12
dB
V
OS
Output Offset Voltage
10
mV
T
WU
Wake-up Time
7
ms
P
o
Output Power
THD = 2% (max); f = 1kHz
1.1
W
THD+N
Total Harmonic Distortion+Noise
P
O
= 100mW
RMS
; f
IN
= 1kHz
0.8
%
R
IN
Differential Input Resistance
V
Gain Select
= V
DD
90
k
V
Gain Select
= GND
60
k
PSRR
Power Supply Rejection Ratio
V
ripple
= 100mV
RMS
sine wave
Inputs terminated to GND
55
(f = 217Hz)
dB
V
Ripple
= 100mV
RMS
sine wave
P
OUT
= 10mW,1kHz
65
(f = 217Hz)
dB
CMRR
Common Mode Rejection Ratio
V
Ripple
= 100mV
RMS
,
f
Ripple
= 217Hz
41
dB
SNR
Signal to Noise Ratio
P
O
= 1W
RMS
, A-Weighted Filter
83
dB
e
OUT
Output Noise
A-Weighted filter, V
in
= 0V
200
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 LM4664, 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.
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.
LM4664
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