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FAN1589DX Datenblatt(PDF) 6 Page - Fairchild Semiconductor |
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FAN1589DX Datenblatt(HTML) 6 Page - Fairchild Semiconductor |
6 / 12 page FAN1589 PRODUCT SPECIFICATION 6 REV. 1.0.5 11/10/03 Applications Information General The FAN1589 is a three-terminal regulator optimized for a GTL+ VTT termination applications. It is short-circuit pro- tected, and offers thermal shutdown to turn off the regulator when the junction temperature exceeds about 150°C. The FAN1589 provides low dropout voltage and fast transient response. Frequency compensation uses capacitors with low ESR while still maintaining stability. This is critical in address- ing the needs of low voltage high speed microprocessor buses like a GTL+. Stability The FAN1589 requires an output capacitor as a part of the frequency compensation. It is recommended to use a 22µF solid tantalum or a 100µF aluminum electrolytic on the out- put to ensure stability. The frequency compensation of these devices optimizes the frequency response with low ESR capacitors. In general, it is suggested to use capacitors with an ESR of <1 Ω. Protection Diodes In normal operation, the FAN1589 does not require any pro- tection diodes. A protection diode between the input and output pins is usu- ally not needed. An internal diode between the input and out- put pins on the FAN1589 can handle microsecond surge currents of 50A to 100A. Even with large value output capacitors it is difficult to obtain those values of surge cur- rents in normal operation. Only with large values of output capacitance, such as 1000 µF to 5000µF, and with the input pin instantaneously shorted to ground can damage occur. A crowbar circuit at the input can generate those levels of cur- rent; a diode from output to input is then recommended, as shown in Figure 9. Usually, normal power supply cycling or system “hot plugging and unplugging” will not generate cur- rent large enough to do any damage. As with any IC regulator, exceeding the maximum input-to- output voltage differential causes the internal transistors to break down and none of the protection circuitry is then functional. Figure 8. Optional Protection Load Regulation It is not possible to provide true remote load sensing because the FAN1589 is a three-terminal device. Load regulation is limited by the resistance of the wire connecting the regula- tors to the load. Load regulation per the data sheet specifica- tion is measured at the bottom of the package. For fixed voltage devices, negative side sensing is a true Kelvin connection with the ground pin of the device returned to the negative side of the load. This is illustrated in Figure 10. Figure 9. Connection for Best Load Regulation Thermal Considerations The FAN1589 protects itself under overload conditions with internal power and thermal limiting circuitry. However, for normal continuous load conditions, do not exceed maximum junction temperature ratings. It is important to consider all sources of thermal resistance from junction-to-ambient. These sources include the junction-to-case resistance, the case-to-heat sink interface resistance, and the heat sink resis- tance. Thermal resistance specifications have been developed to more accurately reflect device temperature and ensure safe operating temperatures. For example, look at using an FAN1589 to generate 2.7A @ 1.2V ± 2% from a 3.3V source (3.2V to 3.6V). Assumptions: •VIN = 3.6V worst case •VOUT = 1.176V worst case •IOUT = 2.7A continuous •TA = 70°C • θCase-to-Ambient = 3°C/W (assuming both a heatsink and a thermally conductive material) The power dissipation in this application is: PD = (VIN – VOUT) * (IOUT) = (3.6 – 1.18) * (2.7) = 6.53W From the specification table: TJ = TA + (PD) * (θCase-to-Ambient + θJC) = 70 + (6.53) * (3 + 3) = 109 °C The junction temperature is below the maximum rating. FAN1589 GND C2 22 µF VOUT C1 10 µF + + IN OUT D1 1N4002 (OPTIONAL) VIN FAN1589 GND RL RP PARASITIC LINE RESISTANCE IN OUT VIN |
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Ähnliche Beschreibung - FAN1589DX |
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