NSC LM3875T, LM3875MWC, LM3875DWF, LM3875TF Datasheet
LM3875
Overture
™
Audio Power Amplifier Series
High-Performance 56W Audio Power Amplifier
General Description
The LM3875 is a high-performance audio power amplifier
capable of delivering 56W of continuous average power to
an 8Ω load with 0.1%(THD + N) from 20 Hz–20 kHz.
The performance of the LM3875, utilizing its Self Peak Instantaneous Temperature (˚Ke) (SPiKe
™
) Protection Circuitry, puts it in a class above discrete and hybrid amplifiers
by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe Protection means that these parts
are completely safeguarded at the output against overvoltage, undervoltage, overloads, including shorts to the supplies, thermal runaway, and instantaneous temperature
peaks.
The LM3875 maintains an excellent Signal-to-Noise Ratio of
greater than 95 dB(min) with a typical low noise floor of
2.0 µV. It exhibits extremely low (THD + N) values of 0.06
%
at the rated output into the rated load over the audio spectrum, and provides excellent linearity with an IMD (SMPTE)
typical rating of 0.004%.
Features
n 56W continuous average output power into 8Ω
n 100W instantaneous peak output power capability
n Signal-to-Noise Ratio
>
95 dB (min)
n Output protection from a short to ground or to the
supplies via internal current limiting circuitry
n Output over-voltage protection against transients from
inductive loads
n Supply under-voltage protection, not allowing internal
biasing to occur when |V
EE
|+|VCC| ≤ 12V, thus
eliminating turn-on and turn-off transients
n 11 lead TO-220 package
Applications
n Component stereo
n Compact stereo
n Self-powered speakers
n Surround-sound amplifiers
n High-end stereo TVs
Typical Application
Overture™and SPiKe™Protection are trademarks of National Semiconductor Corporation.
DS011449-1
*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function
description.
FIGURE 1. Typical Audio Amplifier Application Circuit
June 1999
LM3875 Overture Audio Power Amplifier Series High-Performance 56W Audio Power Amplifier
© 1999 National Semiconductor Corporation DS011449 www.national.com
Connection Diagram
Plastic Package (Note 8)
DS011449-2
Top View
Order Number LM3875T or LM3875TF
See NS Package Number TA11B for
Staggered Lead Non-Isolated Package
or TF11B for Staggered Lead Isolated Package
www.national.com 2
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) 94V
Supply Voltage |V
+
|+|V−| (Input Signal) 84V
Common Mode Input Voltage (V
+
or V−) and
|V
+
|+|V−|≤80V
Differential Input Voltage 60V
Output Current Internally Limited
Power Dissipation (Note 3) 125W
ESD Susceptibility (Note 4) 2500V
Junction Temperature (Note 5) 150˚C
Soldering Information
T package (10 seconds) 260˚C
Storage Temperature −40˚C to +150˚C
Thermal Resistance
θ
JC
1˚C/W
θ
JA
43˚C/W
Operating Ratings (Notes 1, 2)
Temperature Range
T
MIN
≤ TA≤ T
MAX
−20˚C ≤ TA≤ +85˚C
Supply Voltage |V
+
|+|V−| 20V to 84V
Note: Operation is guaranteed up to 84V, however, distortion may be introduced from the SPiKe Protection Circuitry when operating above 70V if
proper thermal considerations are not taken into account. Refer to the Thermal Considerations section for more information. (See SPiKe Protection Response)
Electrical Characteristics (Notes 1, 2)
The following specifications apply for V
+
=
+35V, V
−
=
−35V with R
L
=
8Ω unless otherwise specified. Limits apply for T
A
=
25˚C.
Symbol Parameter Conditions
LM3875
Units
(Limits)
Typical
(Note 6)
Limit
(Note 7)
|V
+
|+|V−| Power Supply Voltage 20
84
V (Min)
V (Max)
**P
O
Output Power (Continuous Average) THD + N=0.1%(Max)
f=1 kHz, f=20 kHz
56 40 W (Min)
Peak P
O
Instantaneous Peak Output Power 100 W
THD + N Total Harmonic Distortion Plus Noise 40W, 20 Hz ≤ f ≤ 20 kHz
A
V
=26dB
0.06
%
**SR Slew Rate (Note 9) V
IN
= 1.414 Vrms,f=10kHz
Square-wave, R
L
=2kΩ
11 5
V/µs
(Min)
*I+ Total Quiescent Power Supply
Current
V
CM
= 0V, VO= 0V, Io=0mA
30 70
mA
(Max)
*V
OS
Input Offset Voltage VCM= 0V, Io=0mA
110
mV
(Max)
I
B
Input Bias Current VCM= 0V, Io=0mA
0.2 1
µA
(Max)
I
OS
Input Offset Current VCM= 0V, Io=0mA
0.01 0.2
µA
(Max)
I
o
Output Current Limit |V+|=|V−|=10V, t
on
=
10 ms, V
O
=
0V 6 4 A(Min)
*V
od
Output Dropout Voltage |V+−V
o
−
|, V
+
=
20V, I
o
=
+100 mA
|V
o
−V−|, V
−
=
−20V, I
o
=
−100 mA
1.6
2.7
5
5
V (Max)
V (Max)
*PSRR Power Supply Rejection Ratio V
+
=
40V to 20V, V
−
=
−40V,
V
cm
=
0V, I
o
=
0mA
V
+
=
40V, V=−40V to −20V,
V
cm
=
0V, I
o
=
0mA
120
120
85
85
dB (Min)
*CMRR Common Mode Rejection Ratio V
+
=
60V to 20V, V
−
=
−20V to −60V,
V
cm
=
20V to −20V, I
o
=
0mA
120 80 dB (Min)
*A
VOL
Open Loop Voltage Gain |V+|=|V−|=40V, R
L
=
2kΩ,∆V
O
=
60V 120 90 dB (Min)
GBWP Gain-Bandwidth Product |V
+
|=|V−|=40V
f
O
=
100 kHz, V
IN
=
50 mVrms
82
MHz
(Min)
**e
IN
Input Noise IHF − A Weighting Filter
R
IN
=
600Ω (Input Referred)
2.0 8.0
µV
(Max)
www.national.com3
Electrical Characteristics (Notes 1, 2) (Continued)
The following specifications apply for V
+
=
+35V, V
−
=
−35V with R
L
=
8Ω unless otherwise specified. Limits apply for T
A
=
25˚C.
Symbol Parameter Conditions
LM3875
Units
(Limits)
Typical
(Note 6)
Limit
(Note 7)
SNR Signal-to-Noise Ratio P
O
=
1W, A-Weighted,
Measured at 1 kHz, R
S
=
25Ω
98 dB dB
P
O
=
40W, A-Weighted,
Measured at 1 kHz, R
S
=
25Ω
114 dB dB
P
pk
=
100W, A-Weighted,
Measured at 1 kHz, R
S
=
25Ω
122 dB dB
IMD Intermodulation Distortion Test 60 Hz, 7 kHz, 4:1 (SMPTE)
60 Hz, 7 kHz, 1:1 (SMPTE)
0.004
0.006
%
*
DC Electrical Test; refer to Test Circuit#1.
**
AC Electrical Test; refer to Test Circuit#2.
Note 1: Absolute Maximum Ratingsindicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which thedevice is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC andAC 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 2: All voltages are measured with respect to supply GND, unless otherwise specified.
Note 3: For operating at case temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance of
θ
JC
=
1.0˚C/W (junction to case). Refer to the Thermal Resistance figure in the Application Information section under Thermal Considerations.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: The operating junction temperature maximum is 150˚C, however, the instantaneous Safe Operating Area temperature is 250˚C.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: The LM3875T packageTA11B is a non-isolated package, setting the tab of the device and the heat sink at V
−
potential when the LM3875 is directly mounted
to the heat sink using only thermal compound. If a mica washer is used in addition to thermal compound, θ
CS
(case to sink) is increased, but the heat sink will be
isolated from V
−
.
Note 9: The feedback compensation network limits the bandwidth of the closed-loop response and so the slew rate will be reduced due to the high frequency roll-off.
Without feedback compensation, the slew rate is typically 16V/µs.
Note 10: 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.
Test Circuit#1 (DC Electrical Test Circuit)
DS011449-3
www.national.com 4
Test Circuit#2 (AC Electrical Test Circuit)
Single Supply Application Circuit
DS011449-4
DS011449-5
*Optional components dependent upon specific design requirements. Refer to the External Components Description section for a component function
description.
FIGURE 2. Typical Single Supply Audio Amplifier Application Circuit
www.national.com5
Equivalent Schematic (Excluding active protection circuitry)
External Components Description
(
Figure 1
and
Figure 2
)
Components Functional Description
1. R
IN
Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.
2. R
A
Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.
3. C
A
Provides bias filtering.
4. C Provides AC coupling at the input and output of the amplifier for single supply operation.
5. R
B
Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load
upon power-down of the system due to the low input impedance of the circuitry when the under-voltage
circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.
6.
*
C
C
Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of
the output transistor. The capacitor also suppresses external electromagnetic switching noise created from
fluorescent lamps.
7. Ri Inverting input resistance to provide AC Gain in conjunction with R
f1
.
8.
*
Ci Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:
f
c
=
1/(2π Ri Ci).
9. R
f1
Feedback resistance to provide AC Gain in conjunction with Ri.
10.
*
R
f2
At higher frequencies feedback resistance works with Cfto provide lower AC Gain in conjunction with R
f1
and Ri. A high frequency pole (lowpass roll-off) exists at:
f
c
=
[R
f1Rf2
](s+1/Rf2Cf]/[(Rf1+Rf2)(s+1/Cf(Rf1+Rf2))].
11.
*
C
f
Compensation capacitor that works with Rf1and Rf2to reduce the AC Gain at higher frequencies.
12.
*
R
SN
Works with CSNto stabilize the output stage by creating a pole that eliminates high frequency oscillations.
13.
*
C
SN
Works with RSNto stabilize the output stage by creating a pole that eliminates high frequency
oscillations. f
c
=
1/(2πR
SNCSN
).
14.
*
L Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce
the Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low
frequencies to short out R and pass audio signals to the load.
15.
*
R
DS011449-6
www.national.com 6
Loading...