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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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LM2876T Fiches technique(PDF) 11 Page - National Semiconductor (TI) |
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LM2876T Fiches technique(HTML) 11 Page - National Semiconductor (TI) |
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11 / 19 page  Typical Performance Characteristics (Continued) Application Information GENERAL FEATURES Mute Function: The muting function of the LM2876 allows the user to mute the music going into the amplifier by draw- ing less than 0.5 mA out of pin 8 of the device. This is accom- plished as shown in the Typical Application Circuit where the resistor R M is chosen with reference to your negative supply voltage and is used in conjuction with a switch. The switch (when opened) cuts off the current flow from pin 8 to V −, thus placing the LM2876 into mute mode. Refer to the Mute At- tenuation vs Mute Current curves in the Typical Perfor- mance Characteristics section for values of attenuation per current out of pin 8. The resistance R M is calculated by the following equation: R M (|VEE| − 2.6V)/I8 where I8 ≥ 0.5 mA. 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 LM2876 such that no DC output spikes occur. Upon turn-off, the output of the LM2876 is brought to ground before the power supplies such that no transients occur at power-down. Over-Voltage Protection: The LM2876 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 LM2876 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 LM2876 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 LM2876 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. 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 θ JC = 1˚C/W and θCS = 0.2˚C/W. We also provide a section regarding heat sink determination for any Power Supply Rejection Ratio DS011775-47 Common-Mode Rejection Ratio DS011775-48 Open Loop Frequency Response DS011775-49 www.national.com 11 |
Numéro de pièce similaire - LM2876T |
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Description similaire - LM2876T |
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