LM4892
1 Watt Audio Power Amplifier with Headphone Sense
General Description
The LM4892 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. Switching between bridged speaker mode and
headphone (single-ended) mode is accomplished using the
headphone sense pin.
Boomer audio power amplifiers are designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4892 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 LM4892 features a low-power consumption shutdown
mode, which is achieved by driving the shutdown pin with
logic low. Additionally, the LM4892 features an internal ther-
mal shutdown protection mechanism.
The LM4892 contains advanced pop & click circuitry which
eliminates noise which would otherwise occur during turn-on
and turn-off transitions.
The LM4892 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: LLP, micro SMD,
MSOP, and SOIC
n
Ultra low current shutdown mode
n
BTL output can drive capacitive loads up to 500pF
n
Improved pop & click circuitry eliminates noise during
turn-on and turn-off transitions
n
2.2 - 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
n
Headphone amplifier mode
Applications
n
Mobile Phones
n
PDAs
n
Portable electronic devices
Typical Application
Boomer
is a registered trademark of National Semiconductor Corporation.
20012701
FIGURE 1. Typical Audio Amplifier Application Circuit (Pin #'s apply to M & MM packages)
October 2002
LM4892
1
W
att
Audio
Power
Amplifier
with
Headphone
Sense
2002 National Semiconductor Corporation
DS200127
www.national.com
Connection Diagrams
8 Bump micro SMD
Small Outline (SO) Package
20012723
Top View
Order Number LM4892IBP, LM4892IBPX
See NS Package Number BPA08DDB
20012735
Top View
Order Number LM4892M
See NS Package Number M08A
Mini Small Outline (MSOP) Package
micro SMD Marking
20012736
Top View
Order Number LM4892MM
See NS Package Number MUA08A
20012770
Top View
X - Date Code
T - Die Traceability
G - Boomer Family
H - LM4892IBP
SO Marking
MSOP Marking
20012772
Top View
XY - Date Code
TT - Die Traceability
Bottom 2 lines - Part Number
20012771
Top View
G - Boomer Family
92 - LM4892MM
LLP Package
20012789
Top View
Order Number LM4892LD
See NS Package Number LDA10B
LM4892
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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
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)
2500V
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 (Note 9)
Soldering Information
See AN-1112 'microSMD Wafers Level Chip Scale
Package'.
See AN-1187 'Leadless 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)
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
LM4892
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A, HP sense = 0V
4
10
mA (max)
V
IN
= 0V, I
o
= 0A, HP sense = 5V
2.5
mA (max)
I
SD
Shutdown Current
Vshutdown = GND (Note 8)
0.1
A (max)
P
o
Output Power
THD = 2% (max), f = 1kHz,
R
L
= 8
, HP Sense
<
0.8V
1
W
THD = 1% (max), f = 1kHz,
R
L
= 32
, HP Sense
>
4V
90
mW
V
IH
HP Sense high input voltage
4
V (min)
V
IL
HP Sense low input voltage
0.8
V (max)
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.4 W
rms
; f = 1kHz 10Hz
BW
80kHz
0.1
%
PSSR
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)
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
LM4892
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A, HP sense = 0V
3.5
mA (max)
V
IN
= 0V, I
o
= 0A, HP sense = 3.3V
2.0
mA (max)
I
SD
Shutdown Current
Vshutdown = GND (Note 8)
0.1
A (max)
P
o
Output Power
THD = 1% (max), f = 1kHz,
R
L
= 8
, HP Sense
<
0.8V
0.4
W
THD = 1% (max), f = 1kHz,
R
L
= 32
, HP Sense
>
3V
35
mW
V
IH
HP Sense high input voltage
2.6
V (min)
V
IL
HP Sense low input voltage
0.8
V (max)
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.15 W
rms
; f = 1kHz 10Hz
BW
80kHz
0.1
%
LM4892
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3
Electrical Characteristics V
DD
= 3.3V
(Notes 1, 2)
The following specifications apply for V
DD
= 3.3V, A
V
= 2, and 8
load unless otherwise specified. Limits apply for T
A
=
25C. (Continued)
Symbol
Parameter
Conditions
LM4892
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
PSSR
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)
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
LM4892
Units
(Limits)
Typical
Limit
(Note 6)
(Note 7)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
o
= 0A, HP sense = 0V
2.6
mA (max)
V
IN
= 0V, I
o
= 0A, HP sense = 2.6V
1.5
mA (max)
I
SD
Shutdown Current
Vshutdown = GND (Note 8)
0.1
A (max)
P
o
Output Power
THD = 1% (max), f = 1kHz,
R
L
= 8
, HP Sense
<
0.8V
0.25
W
THD = 1% (max), f = 1kHz,
R
L
= 4
, HP Sense
<
0.8V
0.28
W
THD = 1% (max), f = 1kHz, R
L
=
32
, HP Sense
>
2.5V
20
mW
V
IH
HP Sense high input voltage
2.0
V (min)
V
IL
HP Sense low input voltage
0.8
V (max)
THD+N
Total Harmonic Distortion+Noise
P
o
= 0.1 W
rms
; f = 1kHz 10Hz
BW
80kHz
0.1
%
PSSR
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 LM4892, see power derating
currents 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: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.
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: The Exposed-DAP of the LDA10B package should be electrically connected to GND or an electrically isolated copper area. The LM4892LD demo board
(views featured in the Application Information section) has the Exposed-DAP connected to GND with a PCB area of 353mils x 86.7mils (8.97mm x 2.20mm) on
the copper top layer and 714.7mils x 368mils (18.15mm x 9.35mm) on the copper bottom layer.
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
.
LM4892
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4
External Components Description
(Figure 1) (Continued)
Components
Functional Description
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
.
6.
C
OUT
This output coupling capacitor blocks DC voltage while coupling the AC audio signal to the headphone
speaker. Combined with R
L
, the headphone impedance, it creates a high pass filter at f
c
= 1/(2
R
L
C
OUT
).
Refer to the section, Proper Selection of External Components for an explanation of how to determine the
value of C
OUT
.
7.
R
PU
This is the pull up resistor to activate headphone operation when a headphone plug is plugged into the
headphone jack.
8.
R
S
This is the current limiting resistor for the headphone input pin.
9.
R
PD
This is the pull down resistor to de-activate headphone operation when no headphone is plugged into the
headphone jack.
Typical Performance Characteristics
THD+N vs Frequency
at V
DD
= 5V, 8
R
L
, and PWR = 250mW
THD+N vs Frequency
at V
DD
= 3.3V, 8
R
L
, and PWR = 150mW
20012737
20012738
THD+N vs Frequency
at V
DD
= 2.6V, 8
R
L
, and PWR = 100mW
THD+N vs Frequency
at V
DD
= 2.6V, 4
R
L
, and PWR = 100mW
20012739
20012740
LM4892
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