LM4906
1W, Bypass-Capacitor-less Audio Amplifier with Internal
Selectable Gain
General Description
The LM4906 is an audio power amplifier primarily designed
for demanding applications in mobile phones and other por-
table communication device applications. It is capable of
delivering 1W of continuous average power to an 8
BTL
load with less than 1% distortion (THD+N) from a +5V power
supply.
The LM4906 is the first National Semiconductor Boomer
Power Amplifier that does not require an external PSRR
bypass capacitor. The LM4906 also has an internal select-
able gain of either 6dB or 12dB. In addition, no output
coupling capacitors or bootstrap capacitors are required
which makes the LM4906 ideally suited for cell phone and
other low voltage portable applications.
The LM4906 contains advanced pop and click circuitry that
eliminates noise, which would otherwise occur during
turn-on and turn-off transitions.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4906 features a low -power
consumption shutdown mode (the part is enabled by pulling
the SD pin high). Additionally, the LM4906 features an inter-
nal thermal shutdown protection mechanism.
Key Specifications
j
Improved PSRR at 217Hz for +3V
71dB
j
Power Output at +5V, THD+N = 1%, 8
1.0W (typ)
j
Power Output at +3V, THD+N = 1%, 8
390mW (typ)
j
Total shutdown power supply current
0.1A (typ)
Features
n
Selectable gain of 6dB (2V/V) or 12dB (4V/V)
n
No output or PSRR bypass capacitors required
n
Improved "Click and Pop" suppression circuitry
n
Very fast turn on time: 5ms (typ)
n
Minimum external components
n
2.6 - 5.5V operation
n
BTL output can drive capacitive loads
n
Ultra low current shutdown mode (SD Low)
Applications
n
Portable computers
n
Desktop computers
n
Multimedia monitors
Typical Application
Boomer
is a registered trademark of National Semiconductor Corporation.
200571B9
FIGURE 1. Typical Audio Amplifier Application Circuit
May 2003
LM4906
1W
,
Bypass-Capacitor-less
Audio
Amplifier
with
Internal
Selectable
Gain
2003 National Semiconductor Corporation
DS200571
www.national.com
Absolute Maximum Ratings
(Note 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (Note 10)
6.0V
Storage Temperature
-65C to +150C
Input Voltage
-0.3V to V
DD
+0.3V
Power Dissipation (Notes 3, 11)
Internally Limited
ESD Susceptibility (Note 4)
2000V
ESD Susceptibility (Note 5)
200V
Junction Temperature
150C
Thermal Resistance
JC
(MSOP)
56C/W
JA
(MSOP)
190C/W
JC
(LLP)
12C/W
JA
(LLP)
63C/W
Operating Ratings
Temperature Range
T
MIN
T
A
T
MAX
-40C
T
A
85C
Supply Voltage
2.6V
V
DD
5.5V
Electrical Characteristics V
DD
= 5V
(Notes 1, 2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4906
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A, No Load
3.5
7
mA (max)
V
IN
= 0V, I
o
= 0A, 8
Load
4
8
mA (max)
I
SD
Shutdown Current
V
SD
= GND
0.1
2
A (max)
V
OS
Output Offset Voltage
7
35
mV (max)
P
o
Output Power
THD+N = 1% (max); f = 1 kHz
R
L
= 8
1.0
0.9
W (min)
T
WU
Wake-up time
5
ms
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.4 Wrms; f = 1kHz
0.2
%
PSRR
Power Supply Rejection Ratio
V
ripple
= 200mV sine p-p
Input terminated with 10
Gain at 6dB
67 (f =
217Hz)
70 (f = 1kHz)
dB
V
SDIH
Shutdown Voltage Input High
SD Pin High = Part On
1.5
V (min)
V
SDIL
Shutdown Voltage Input Low
SD Pin Low = Part Off
1.3
V (max)
Electrical Characteristics V
DD
= 3V
(Notes 1, 2)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4906
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A, No Load
2.6
6
mA (max)
V
IN
= 0V, I
o
= 0A, 8
Load
3
7
mA (max)
I
SD
Shutdown Current
V
SD
= GND
0.1
2
A (max)
V
OS
Output Offset Voltage
7
35
mV (max)
P
o
Output Power
THD+N = 1% (max); f = 1 kHz
R
L
= 8
390
mW
T
WU
Wake-up time
4
ms
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.15 Wrms; f = 1kHz
0.1
%
PSRR
Power Supply Rejection Ratio
V
ripple
= 200mV sine p-p
Input terminated with 10
Gain at 6dB
71 (f =
217Hz)
73 (f = 1kHz)
dB
V
SDIH
Shutdown Voltage Input High
SD Pin High = Part On
1.1
V (min)
V
SDIL
Shutdown Voltage Input Low
SD Pin Low = Part Off
0.9
V (max)
LM4906
www.national.com
3
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 LM4906, see power derating
curves for additional information.
Note 4: Human body model, 100pF discharged through a 1.5k
resistor.
Note 5: Machine Model, 220pF240pF discharged through all pins.
Note 6: Typicals are measured at 25C and represent the parametric norm.
Note 7: 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: R
OUT
is measured from the output pin to ground. This value represents the parallel combination of the 10k
output resistors and the two 20k resistors.
Note 10: If the product is in Shutdown mode and V
DD
exceeds 6V (to a max of 8V V
DD
), then most of the excess current will flow through the ESD protection circuits.
If the source impedance limits the current to a max of 10mA, then the device will be protected. If the device is enabled when V
DD
is greater than 5.5V and less than
6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage.
Note 11: Maximum power dissipation in the device (P
DMAX
) occurs at an output power level significantly below full output power. P
DMAX
can be calculated using
Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs.
External Components Description
Components
Functional Description
1.
C
2
Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a
highpass filter with R
i
at f
c
= 1 / (2
R
i
C
i
). Refer to the section, Proper Selection of External Components,
for an explanation of how to determine the value of C
i
.
2.
C
1
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.
LM4906
www.national.com
4
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