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PDF LM3875 Data sheet ( Hoja de datos )
| Número de pieza | LM3875 | |
| Descripción | LM3875 Overture Audio Power Amplifier Series High-Performance 56W Audio Power Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM3875 (archivo pdf) en la parte inferior de esta página. Total 19 Páginas | ||
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June 1999
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 In-
stantaneous Temperature (˚Ke) (SPiKe™) Protection Cir-
cuitry, puts it in a class above discrete and hybrid amplifiers
by providing an inherently, dynamically protected Safe Oper-
ating Area (SOA). SPiKe Protection means that these parts
are completely safeguarded at the output against overvolt-
age, undervoltage, overloads, including shorts to the sup-
plies, 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 spec-
trum, 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 |VEE| + |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
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
Overture™ and SPiKe™ Protection are trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS011449
www.national.com
1 page  
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
5 www.national.com
5 Page 
Typical Performance Characteristics (Continued)
Pulse Response
Open Loop
Frequency Response
DS011449-47
Application Information
GENERAL FEATURES
Under-Voltage Protection: Upon system power-up the
under-voltage Protection Circuitry allows the power supplies
and their corresponding caps to come up close to their full
values before turning on the LM3875 such that no DC output
spikes occur. Upon turn-off, the output of the LM3875 is
brought to ground before the power supplies such that no
transients occur at power-down.
Over-Voltage Protection: The LM3875 contains overvolt-
age protection circuitry that limits the output current to ap-
proximately 4Apeak while also providing voltage clamping,
though not through internal clamping diodes. The clamping
effect is quite the same, however, the output transistors are
designed to work alternately by sinking large current spikes.
SPiKe Protection: The LM3875 is protected from instanta-
neous peak-temperature stressing by the power transistor
array. The Safe Operating Area graph in the Typical Perfor-
mance Characteristics section shows the area of device
operation where the SPiKe Protection Circuitry is not en-
abled. The waveform to the right of the SOA graph exempli-
fies how the dynamic protection will cause waveform distor-
tion when enabled.
Thermal Protection: The LM3875 has a sophisticated ther-
mal protection scheme to prevent long-term thermal stress
to the device. When the temperature on the die reaches
165˚C, the LM3875 shuts down. It starts operating again
when the die temperature drops to about 155˚C, but if the
temperature again begins to rise, shutdown will occur again
at 165˚C. Therefore the device is allowed to heat up to a
relatively high temperature if the fault condition is temporary,
but a sustained fault will cause the device to cycle in a
Schmitt Trigger fashion between the thermal shutdown tem-
perature limits of 165˚C and 155˚C. This greatly reduces the
stress imposed on the IC by thermal cycling, which in turn
improves its reliability under sustained fault conditions.
Since the die temperature is directly dependent upon the
heat sink, the heat sink should be chosen as discussed in
the Thermal Considerations section, such that thermal
shutdown will not be reached during normal operation. Using
the best heat sink possible within the cost and space con-
straints of the system will improve the long-term reliability of
any power semiconductor device.
DS011449-48
THERMAL CONSIDERATIONS
Heat Sinking
The choice of a heat sink for a high-power audio amplifier is
made entirely to keep the die temperature at a level such
that the thermal protection circuitry does not operate under
normal circumstances. The heat sink should be chosen to
dissipate the maximum IC power for a given supply voltage
and rated load.
With high-power pulses of longer duration than 100 ms, the
case temperature will heat up drastically without the use of a
heat sink. Therefore the case temperature, as measured at
the center of the package bottom, is entirely dependent on
heat sink design and the mounting of the IC to the heat sink.
For the design of a heat sink for your audio amplifier applica-
tion refer to the Determining the Correct Heat Sink sec-
tion.
Since a semiconductor manufacturer has no control over
which heat sink is used in a particular amplifier design, we
can only inform the system designer of the parameters and
the method needed in the determination of a heat sink. With
this in mind, the system designer must choose his supply
voltages, a rated load, a desired output power level, and
know the ambient temperature surrounding the device.
These parameters are in addition to knowing the maximum
junction temperature and the thermal resistance of the IC,
both of which are provided by National Semiconductor.
As a benefit to the system designer we have provided Maxi-
mum Power Dissipation vs Supply Voltages curves for vari-
ous loads in the Typical Performance Characteristics sec-
tion, giving an accurate figure for the maximum thermal
resistance required for a particular amplifier design. This
data was based on θJC = 1˚C/W and θCS = 0.2˚C/W. We also
provide a section regarding heat sink determination for any
audio amplifier design where θCS may be a different value. It
should be noted that the idea behind dissipating the maxi-
mum power within the IC is to provide the device with a low
resistance to convection heat transfer such as a heat sink.
Therefore, it is necessary for the system designer to be con-
servative in his heat sink calculations. As a rule, the lower
the thermal resistance of the heat sink the higher the amount
of power that may be dissipated. This is, of course, guided
by the cost and size requirements of the system. Convection
cooling heat sinks are available commercially, and their
manufacturers should be consulted for ratings.
11 www.national.com
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet LM3875.PDF ] | |
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