LM4891
1 Watt Audio Power Amplifier
General Description
The LM4891 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 1 watt of continuous average power to an 8
BTL
load with less than 1% distortion (THD+N) from a 5V
DC
power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4891 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli-
cations where minimal power consumption is a primary re-
quirement.
The LM4891 features a low-power consumption shutdown
mode, which is achieved by driving the shutdown pin with
logic high. Additionally, the LM4891 features an internal ther-
mal shutdown protection mechanism.
The LM4891 contains advanced pop & click circuitry which
eliminates noises which would otherwise occur during
turn-on and turn-off transitions.
The LM4891 is unity-gain stable and can be configured by
external gain-setting resistors.
Key Specifications
j
PSRR at 217Hz, V
DD
= 5V, 8
Load
62dB (typ)
j
Power Output at 5.0V & 1% THD
1.0W (typ)
j
Power Output at 3.3V & 1% THD
400mW (typ)
j
Shutdown Current
0.1A (typ)
Features
n
Available in space-saving packages: micro SMD, MSOP,
SOIC, and LLP
n
Ultra low current shutdown mode
n
BTL output can drive capacitive loads
n
Improved pop & click circuitry eliminates noises during
turn-on and turn-off transitions
n
2.2 to 5.5V operation
n
No output coupling capacitors, snubber networks or
bootstrap capacitors required
n
Thermal shutdown protection
n
Unity-gain stable
n
External gain configuration capability
Applications
n
Mobile Phones
n
PDAs
n
Portable electronic devices
Typical Application
Boomer
is a registered trademark of National Semiconductor Corporation.
20007401
FIGURE 1. Typical Audio Amplifier Application Circuit
October 2002
LM4891
1
W
att
Audio
Power
Amplifier
2002 National Semiconductor Corporation
DS200074
www.national.com
Connection Diagrams
8 Bump micro SMD
Small Outline (SO) Package
20007423
Top View
Order Number LM4891IBP, LM4891IBPX
See NS Package Number BPA08DDB
20007435
Top View
Order Number LM4891M
See NS Package Number M08A
8 Bump micro SMD Marking
SO Marking
20007470
Top View
X - Date Code
T - Die Traceability
G - Boomer Family
G - LM4891IBP
20007472
Top View
XY - Date Code
TT - Die Traceability
Bottom 2 lines - Part Number
Mini Small Outline (MSOP) Package
MSOP Marking
20007436
Top View
Order Number LM4891MM
See NS Package Number MUA08A
20007471
Top View
G - Boomer Family
91 - LM4891MM
LLP Package
10 Pin LLP Marking
20007480
Top View
Order Number LM4891LD
See NS Package Number LDA10B
20007479
Top View
Z - Assembly Plant Code (M for Malacca)
XY - 2 Digit Datecode
TT - 2 Letter Code for Traceability
L4891 - LM4891LD
LM4891
www.national.com
2
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 11)
6.0V
Storage Temperature
-65C to +150C
Input Voltage
-0.3V to V
DD
+0.3V
Power Dissipation (Note 3)
Internally Limited
ESD Susceptibility (Note 4)
2000V
ESD Susceptibility (Note 5)
250V
Junction Temperature
150C
Thermal Resistance
JC
(SOP)
35C/W
JA
(SOP)
150C/W
JA
(micro SMD)
220C/W
JC
(MSOP)
56C/W
JA
(MSOP)
190C/W
JA
(LLP)
220C/W
Soldering Information
See AN-1112 "microSMD Wafers Level Chip Scale
Package".
See AN-1187 "Leadlesss
Leadframe Package (LLP)".
Operating Ratings
Temperature Range
T
MIN
T
A
T
MAX
-40C
T
A
85C
Supply Voltage
2.2V
V
DD
5.5V
Electrical Characteristics V
DD
= 5V
(Notes 1, 2, 8)
The following specifications apply for V
DD
= 5V, A
V
= 2, and 8
load unless otherwise specified. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4891
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A
4
10
mA (max)
I
SD
Shutdown Current
V
shutdown
= V
DD
0.1
A (max)
P
o
Output Power
THD = 2% (max); f = 1 kHz
1
W
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.4 Wrms; f = 1kHz
0.1
%
PSRR
Power Supply Rejection Ratio
V
ripple
= 200mV sine p-p
62 (f =
217Hz)
66 (f = 1kHz)
dB
Electrical Characteristics V
DD
= 3.3V
(Notes 1, 2, 8)
The following specifications apply for V
DD
= 3.3V, A
V
= 2, and 8
load unless otherwise specified. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4891
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A
3.5
mA (max)
I
SD
Shutdown Current
V
shutdown
= V
DD
0.1
A (max)
P
o
Output Power
THD = 1% (max); f = 1kHz
0.4
W
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.15Wrms; f = 1kHz
0.1
%
PSRR
Power Supply Rejection Ratio
V
ripple
= 200mV sine p-p
60 (f =
217Hz)
62 (f = 1kHz)
dB
Electrical Characteristics V
DD
= 2.6V
(Notes 1, 2, 8)
The following specifications apply for V
DD
= 2.6V, A
V
= 2, and 8
Load unless otherwise specified. Limits apply for T
A
=
25C.
Symbol
Parameter
Conditions
LM4891
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A
2.6
mA (max)
I
SD
Shutdown Current
V
shutdown
= V
DD
0.1
A (max)
LM4891
www.national.com
3
Electrical Characteristics V
DD
= 2.6V
(Notes 1, 2, 8)
The following specifications apply for V
DD
= 2.6V, A
V
= 2, and 8
Load unless otherwise specified. Limits apply for T
A
=
25C. (Continued)
Symbol
Parameter
Conditions
LM4891
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
P
0
Output Power ( 8
)
Output Power ( 4
)
THD = 1% (max); f = 1 kHz THD =
1% (max); f = 1 kHz
0.25
0.28
W
W
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.1Wrms; f = 1kHz
0.08
%
PSRR
Power Supply Rejection Ratio
V
ripple
= 200mV sine p-p
44 (f =
217Hz)
44 (f = 1kHz)
dB
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 LM4891, see power derating
curves for additional 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: 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: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase I
SD
by a maximum of 2A.
Note 9: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 10: ROUT is measured from each of the output pins to ground. This value represents the parallel combination of the 10k ohm output resistors and the two 20k
ohm resistors.
Note 11: 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 10 ma, then the part will be protected. If the part is enabled when V
DD
is greater than 5.5V and less than 6.5V,
no damage will occur, although operational life will be reduced. Operation above 6.5V with no current limit will result in permanent damage.
Note 12: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. All bumps must be connected to achieve
specified thermal resistance.
Note 13: Maximum power dissipation (P
DMAX
) in the device occurs at an output power level significantly below full output power. P
DMAX
can be calculated using
Equation 1 shown in the Application section. It may also be obtained from the power dissipation graphs.
Note 14: PSRR is a function of system gain. Specifications apply to the circuit in Figure 1 where A
V
= 2. Higher system gains will reduce PSRR value by the amount
of gain increase. A system gain of 10 represents a gain increase of 14dB. PSRR will be reduced by 14dB and applies to all operating voltages.
External Components Description
(Figure 1)
Components
Functional Description
1.
R
i
Inverting input resistance which sets the closed-loop gain in conjunction with R
f
. This resistor also forms a
high pass filter with C
i
at f
C
= 1/(2
R
i
C
i
).
2.
C
i
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
.
3.
R
f
Feedback resistance which sets the closed-loop gain in conjunction with R
i
.
4.
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.
5.
C
B
Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External
Components, for information concerning proper placement and selection of C
B
.
LM4891
www.national.com
4
PDF 
ZIP