LM4781 Overture
TM
Audio Power Amplifier Series
3 Channel 35W Audio Power Amplifier with Mute
General Description
The LM4781 is a three channel audio amplifier capable of
typically delivering 35W per channel of continuous average
output power into an 8
load with less than 0.5% THD+N
from 20Hz - 20kHz.
The LM4781 is fully protected utilizing National's Self Peak
Instantaneous Temperature (Ke) (SPiKe
TM
) protection cir-
cuitry. SPiKe provides a dynamically optimized Safe Operat-
ing Area (SOA). SPiKe protection completely safeguards the
LM4781's outputs against over-voltage, under-voltage, over-
loads, shorts to the supplies or GND, thermal runaway and
instantaneous temperature peaks. The advanced protection
features of the LM4781 places it in a class above discrete
and hybrid amplifiers.
Each amplifier of the LM4781 has an independent smooth
transition fade-in/out mute.
The LM4781 can easily be configured for bridge or parallel
operation for higher power and bi-amp solutions.
Key Specifications
j
Output Power/Channel with 0.5% THD+N,
1kHz into 8
35W (typ)
j
THD+N at 3 x 20W into 8
(20Hz - 20kHz) 0.2% (typ)
j
THD+N at 3 x 20W into 6
(20Hz - 20kHz) 0.3% (typ)
j
THD+N at 3 x 20W into 4
(20Hz - 20kHz) 0.5% (typ)
j
Mute Attenuation
110dB (typ)
j
PSRR
85dB (min)
j
Slew Rate
9V/s (typ)
Features
n
SPiKe Protection
n
Low external component count
n
Quiet fade-in/out mute mode
n
Wide supply range: 20V - 70V
n
Signal-to-Noise Ratio
93dB (ref. to P
O
= 1W)
Applications
n
Audio amplifier for component stereo
n
Audio amplifier for compact stereo
n
Audio amplifier for self-powered speakers
n
Audio amplifier for high-end and HD TVs
Typical Application
SPiKe
TM
Protection and Overture
TM
are trademarks of National Semiconductor Corporation.
200673B5
FIGURE 1. Typical Audio Amplifier Application Circuit
August 2003
LM4781
Overture
TM
Audio
Power
Amplifier
Series
3
Channel
35W
Audio
Power
Amplifier
with
Mute
2003 National Semiconductor Corporation
DS200673
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 |V
+
| + |V
-
|
(No Signal)
72V
Supply Voltage |V
+
| + |V
-
|
(Input Signal)
70V
Common Mode Input Voltage
(V
+
or V
-
) and
|V
+
| + |V
-
|
60V
Differential Input Voltage (Note 13)
60V
Output Current
Internally Limited
Power Dissipation (Note 3)
125W
ESD Susceptability (Note 4)
2.0kV
ESD Susceptability (Note 5)
200V
Junction Temperature (T
JMAX
) (Note 9)
150C
Soldering Information
TA Package (10 seconds)
260C
Storage Temperature
-40C to +150C
Thermal Resistance
JA
30C/W
JC
0.9C/W
Operating Ratings
(Notes 1, 2)
Temperature Range
T
MIN
T
A
T
MAX
-20C
T
A
+85C
Supply Voltage |V
+
| + |V
-
|
20V
V
TOTAL
70V
Note: Operation is guaranteed up to 70V; however, distor-
tion may be introduced from SPiKe protection circuitry if
proper thermal considerations are not taken into account.
Refer to the Thermal Considerations section for more
information.
Electrical Characteristics
(Notes 1, 2)
The following specifications apply for V
+
= +28V, V
-
= -28V, I
MUTE
= -1mA/channel and R
L
= 8
unless otherwise specified.
Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4781
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
|V
+
| + |V
-
|
Power Supply Voltage (Note
10)
GND - V
-
9V
18
20
70
V (min)
V (max)
A
M
Mute Attenuation
I
MUTE
= 0mA
110
80
dB (min)
P
O
Output Power (RMS)
THD+N = 0.5% (max)
f = 1kHz
|V
+
| = |V
-
| = 20V, R
L
= 4
|V
+
| = |V
-
| = 24V, R
L
= 6
|V
+
| = |V
-
| = 28V, R
L
= 8
25
30
35
20
25
30
W (min)
W (min)
W (min)
THD+N
Total Harmonic Distortion +
Noise
P
O
= 20W, f = 20Hz - 20kHz
A
V
= 26dB
|V
+
| = |V
-
| = 20V, R
L
= 4
|V
+
| = |V
-
| = 24V, R
L
= 6
|V
+
| = |V
-
| = 28V, R
L
= 8
0.5
0.3
0.2
%
%
%
X
talk
Channel Separation (Note 11)
P
O
= 10W, f = 1kHz
70
dB
P
O
= 10W, f = 10kHz
66
dB
SR
Slew Rate
V
IN
= 1.2V
RMS
, f = 10kHz square
Wave.R
L
= 2k
9
5
V/s (min)
I
DD
Total Quiescent Power
V
CM
= 0V
75
150
mA (max)
Supply Current
V
O
= 0V, I
O
= 0A
V
OS
Input Offset Voltage
V
CM
= 0V, I
O
= 0mA
1
10
mV (max)
I
B
Input Bias Current
V
CM
= 0V, I
O
= 0mA
0.2
1
A (max)
I
O
Output Current Limit
|V
+
| = |V
-
| = 20V, t
ON
= 10ms
4
3
A (min)
V
OD
Output Dropout Voltage (Note
12)
|V
+
- V
O
|, V
+
= 20V, I
O
= +100mA
|V
O
- V
-
|, V
-
= -20V, I
O
= -100mA
1.5
2.5
4
4
V (max)
V (max)
PSRR
Power Supply Rejection Ratio
(Note 15)
V
+
= 30V to 10V, V
-
= -30V
V
CM
= 0V, I
O
= 0mA
125
85
dB (min)
V
+
= 30V, V
-
= -30V to -10V
V
CM
= 0V, I
O
= 0mA
110
85
dB (min)
LM4781
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3
Electrical Characteristics
(Notes 1, 2) (Continued)
The following specifications apply for V
+
= +28V, V
-
= -28V, I
MUTE
= -1mA/channel and R
L
= 8
unless otherwise specified.
Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4781
Units
(Limits)
Typical
Limit
(Note 6)
(Notes 7, 8)
CMRR
Common Mode Rejection Ratio
(Note 15)
V
+
= 30V to 10V, V
-
= -10V to -30V
V
CM
= 20V to -20V, I
O
= 0mA
110
75
dB (min)
A
VOL
Open Loop Voltage Gain
|V
+
| = |V
-
| = 28V, R
L
= 2k
V
O
= 20V
115
80
dB (min)
GBWP
Gain Bandwidth Product
|V
+
| = |V
-
| = 28V, f
IN
= 100kHz
V
IN
= 50mV
RMS
8
2
MHz (min)
e
IN
Input Noise
IHF-A-Weighting Filter,
R
IN
= 600
(Input Referred)
3.0
8
V (max)
SNR
Signal-to-Noise Ratio
P
O
= 1W
RMS
; A-Weighted Filter
f
IN
= 1kHz, R
S
= 25
93
dB
P
O
= 25W
RMS
; A-Weighted Filter
f
IN
= 1kHz, R
S
= 25
107
dB
IMD
Intermodulation Distortion
60Hz, 7kHz, 4:1 (SMPTE)
60Hz, 7kHz, 1:1 (SMPTE)
0.004
0.006
%
%
Note 1: All voltages are measured with respect to the ground pins, 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 de-rated at elevated temperatures and is dictated by T
JMAX
,
JC
, and the ambient temperature T
A
. The maximum
allowable power dissipation is P
DMAX
= (T
JMAX
-T
A
)/
JC
or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4781, T
JMAX
= 150C
and the typical
JC
is 0.9C/W. Refer to the DETERMINING THE CORRECT HEAT SINK section for more information.
Note 4: Human body model, 100pF discharged through a 1.5k
resistor.
Note 5: Machine Model: a 220pF - 240pF discharged through all pins.
Note 6: Typical specifications are measured 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: The maximum operating junction temperature is 150C. However, the instantaneous Safe Operating Area temperature is 250C.
Note 10: V
-
must have at least - 9V at its pin with reference to GND in order for the under-voltage protection circuitry to be disabled. In addition, the voltage
differential between V
+
and V
-
must be greater than 14V.
Note 11: Cross talk performance was measured using the demo board shown in the datasheet. PCB layout will affect cross talk. It is recommended that the input
and output traces be separated by as much distance as possible. Return ground traces from outputs should also be independent back to sinlge ground point and
use as wide of traces as possible.
Note 12: The output dropout voltage is the supply voltage minus the clipping voltage. Refer to the Clipping Voltage vs. Supply Voltage graph in the Typical
Performance Characteristics section.
Note 13: The Differential Input Voltage Absolute Maximum Rating is based on supply voltages V
+
= 30V and V
-
= - 30V.
Note 14: The TA27A is a non-isolated package. The package's metal back and any heat sink to which it is mounted are connected to the V
-
potential when using
only thermal compound. If a mica washer is used in addition to thermal compound,
CS
(case to sink) is increased, but the heat sink will be electrically isolated from
V
-
.
Note 15: DC electrical test.
LM4781
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4
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