LM4938
Stereo 2W Audio Power Amplifiers
with DC Volume Control and Selectable Gain
General Description
The LM4938 is a monolithic integrated circuit that provides
DC volume control, and stereo bridged audio power amplifi-
ers capable of producing 2W into 4
(Note 1) with less than
1.0% THD or 2.2W into 3
(Note 2) with less than 1.0%
THD.
Boomer
audio integrated circuits were designed specifically
to provide high quality audio while requiring a minimum
amount of external components. The LM4938 incorporates a
DC volume control, stereo bridged audio power amplifiers
and a selectable gain or bass boost, making it optimally
suited for multimedia monitors, portable radios, desktop, and
portable computer applications.
The LM4938 features an externally controlled, low-power
consumption shutdown mode, and both a power amplifier
and headphone mute for maximum system flexibility and
performance.
Note 1: When properly mounted to the circuit board, LM4938MH will deliver
2W into 4
. See Application Information section Exposed-DAP package
PCB Mounting Considerations for more information.
Note 2: An LM4938MH that has been properly mounted to the circuit board
and forced-air cooled will deliver 2.2W into 3
.
Key Specifications
n
P
O
at 1% THD+N
n
into 3
2.2W (typ)
n
into 4
2.0W (typ)
n
into 8
1.3W (typ)
n
Single-ended mode - THD+N at 92mW into
32
1.0%(typ)
n
Shutdown current
0.5A (typ)
Features
n
Improved click and pop circuitry virtually eliminates
noise during turn on/off transitions
n
DC Volume Control Interface
n
System Beep Detect
n
Stereo switchable bridged/single-ended power amplifiers
n
Selectable internal/external gain and bass boost
n
Thermal shutdown protection circuitry
n
Unity gain stable
Applications
n
Flat Panel Displays
n
Portable and Desktop Computers
n
Multimedia Monitors
n
Portable Radios, PDAs, and Portable TVs
Block Diagram
Boomer
is a registered trademark of NationalSemiconductor Corporation.
20095601
FIGURE 1. LM4938 Block Diagram
February 2005
LM4938
Stereo
2W
Audio
Power
Amplifiers
with
DC
V
olume
Control
and
Selectable
Gain
2005 National Semiconductor Corporation
DS200956
www.national.com
Connection Diagram
TSSOP Package
20095602
Top View
Order Number LM4938MH
See NS Package Number MXA28A for Exposed-DAP TSSOP
LM4938
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2
Absolute Maximum Ratings
(Note 10)
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 11)
Internally limited
ESD Susceptibility (Note 12)
2000V
ESD Susceptibility (Note 13)
200V
Junction Temperature
150C
Soldering Information
Small Outline Package
Vapor Phase (60 sec.)
215C
Infrared (15 sec.)
220C
See AN-450 "Surface Mounting and their Effects on
Product Reliability" for other methods of soldering surface
mount devices.
JC
(typ) - MXA28A
2C/W
JA
(typ) - MXA28A (exposed DAP) (Note 3)
41C/W
JA
(typ) - MXA28A (exposed DAP) (Note 4)
54C/W
JA
(typ) - MXA28A (exposed DAP) (Note 5)
59C/W
JA
(typ) - MXA28A (exposed DAP) (Note 6)
93C/W
Operating Ratings
Temperature Range
T
MIN
T
A
T
MAX
-20C
TA 85C
Supply Voltage
2.7V
V
DD
5.5V
Electrical Characteristics for Entire IC
(Notes 7, 10)
The following specifications apply for V
DD
= 5V unless otherwise noted. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4938
Units
(Limits)
Typical
(Note 14)
Limit
(Note 15)
V
DD
Supply Voltage
2.7
V (min)
5.5
V (max)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
O
= 0A
11
30
mA (max)
I
SD
Shutdown Current
V
shutdown
= V
DD
0.5
2.0
A (max)
V
IH
Headphone Sense High Input Voltage
4
V (min)
V
IL
Headphone Sense Low Input Voltage
0.8
V (max)
Electrical Characteristics for Volume Attenuators
(Notes 7, 10)
The following specifications apply for V
DD
= 5V. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4938
Units
(Limits)
Typical
(Note 14)
Limit
(Note 15)
C
RANGE
Attenuator Range
Gain accuracy with V
DCVol
= 5V,
No Load
0.5
0.75
dB (max)
Gain accuracy with V
DCVol
<
0.5V,
No Load
2
dB (max)
Attenuation with V
DCVol
= 0V
(BM & SE)
89
75
dB (min)
A
M
Mute Attenuation
V
mute
= 5V, Bridged Mode (BM)
89
78
dB (min)
V
mute
= 5V, Single-Ended Mode (SE)
78
dB (min)
Electrical Characteristics for Bridged Mode Operation
(Notes 7, 10)
The following specifications apply for V
DD
= 5V, unless otherwise noted. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4938
Units
(Limits)
Typical
(Note 14)
Limit
(Note 15)
V
OS
Output Offset Voltage
V
IN
= 0V, No Load
5
50
mV (max)
LM4938
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3
Electrical Characteristics for Bridged Mode Operation
(Notes 7, 10) (Continued)
The following specifications apply for V
DD
= 5V, unless otherwise noted. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4938
Units
(Limits)
Typical
(Note 14)
Limit
(Note 15)
P
O
Output Power
THD + N = 1.0%; f = 1kHz
R
L
= 3
(Note 8)
2.2
W
THD + N = 1.0%; f = 1kHz
R
L
= 4
(Note 9)
2
W
THD = 1% (max); f = 1kHz
R
L
= 8
1.3
1.0
W (min)
THD+N = 10%; f = 1 kHz; R
L
= 8
1.5
W
THD+N
Total Harmonic Distortion + Noise
P
O
= 0.4W, f = 1kHz,
R
L
= 8
, A
VD
= 2
0.05
%
PSRR
Power Supply Rejection Ratio
C
B
= 1.0 F, f = 120 Hz,
V
RIPPLE
= 200 mVrms; R
L
= 8
,
Floating
78
dB
C
B
= 1.0 F, f = 120 Hz,
V
RIPPLE
= 200 mVrms; R
L
= 8
,
Terminated
60
dB
SNR
Signal to Noise Ratio
V
DD
= 5V, P
OUT
= 1.2W, R
L
= 8
,
A-Wtd Filter, 1kHz
100
dB
X
talk
Channel Separation
f = 1kHz, C
B
= 1.0F, 1W
76
dB
Electrical Characteristics for Single-Ended Mode Operation
(Notes 7, 10)
The following specifications apply for V
DD
= 5V. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4938
Units
(Limits)
Typical
(Note 14)
Limit
(Note 15)
P
O
Output Power
THD = 1.0%; f = 1kHz; R
L
= 32
92
mW
THD+N
Total Harmonic Distortion + Noise
V
OUT
= 1V
RMS
, f = 1kHz,
R
L
= 10k
, A
VD
= 1
0.065
%
PSRR
Power Supply Rejection Ratio
C
B
= 1.0 F, f = 120 Hz,
V
RIPPLE
= 200 mVrms, Floating
63
dB
C
B
= 1.0 F, f = 120 Hz,
V
RIPPLE
= 200 mVrms, Terminated
59
dB
SNR
Signal to Noise Ratio
P
OUT
= 75mW, R
L
= 32
,
A-Wtd Filter
100
dB
X
talk
Channel Separation
f = 1kHz, C
B
= 1.0 F
73
dB
LM4938
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4
Electrical Characteristics for Single-Ended Mode Operation
(Notes 7,
10) (Continued)
Note 3: The
JA
given is for an MXA28A package whose exposed-DAP is soldered to an exposed 2in
2
piece of 1 ounce printed circuit board copper.
Note 4: The
JA
given is for an MXA28A package whose exposed-DAP is soldered to a 2in
2
piece of 1 ounce printed circuit board copper on a bottom side layer
through 21 8mil vias.
Note 5: The
JA
given is for an MXA28A package whose exposed-DAP is soldered to an exposed 1in
2
piece of 1 ounce printed circuit board copper.
Note 6: The
JA
given is for an MXA28A package whose exposed-DAP is not soldered to any copper.
Note 7: All voltages are measured with respect to the ground pins, unless otherwise specified. All specifications are tested using the typical application as shown
in Figure 1.
Note 8: When driving 3
loads from a 5V supply the LM4938MH must be mounted to the circuit board and forced-air cooled.
Note 9: When driving 4
loads from a 5V supply the LM4938MH must be mounted to the circuit board.
Note 10: 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 11: 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
. For the LM4938, T
JMAX
= 150C, and the typical junction-to-ambient thermal resistance for each package
can be found in the Absolute Maximum Ratings section above.
Note 12: Human body model, 100pF discharged through a 1.5k
resistor.
Note 13: Machine Model, 200pF 220pF discharged through all pins.
Note 14: Typicals are measured at 25C and represent the parametric norm.
Note 15: Limits are guaranteed to National's AOQL ( Average Outgoing Quality Level). Datasheet min/max specification limits are guaranteed by design, test, or
statistical analysis.
LM4938
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