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SPX1583T5-2-8 Datasheet(PDF) 3 Page - Exar Corporation |
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SPX1583T5-2-8 Datasheet(HTML) 3 Page - Exar Corporation |
3 / 5 page D ate: Jun 24-04 SPX1583 Note that TAB is internally connected to Pin 3. BLOCK DIAGRAM APPLICATIONS NOTES The SPX1583 is designed as a high performance and low cost solution for application requiring a lower dropout than traditional NPN regulators. The SPX1583 uses a separate input voltage VCTRL (VCTRL ≥ VOUT+ 1.3V) to minimize the dropout voltage. This allows the 2.5V power for the load to come from a 3.3V system supply. As added benefit this will reduce the heat dissipation, and lower heatsink and cooling fan cost. A typical application would use 5V for Vin and 3.3V for VCTRL from a motherboard power supply to provide a nominal 2.5V output. Using the sense pin allows to Kelvin measure the output, reducing resistive-associated errors. The SPX1583 can power the 2.5V core voltage for microprocessors such as Pentium , P55C, AMD5k86 and K6 and the IBM PowerPC 603EV and 604EV processors. *The reduction of heat dissipation is a result of the increase of the regulator efficiency (efficiency = VOUT / VIN). Adjustable Regulator Design 1.25V reference voltage is being developed between the SENSE pin and the ADJ pin of the SPX1583. Adding two external resistors (see fig 1.) will allow setting the output voltage from 1.25V to 6V. R1 is chosen so that this current is specified minimum load current of 10mA. R2 is given by the formula: VOUT = VREF (1+ R2/R1) + IADJ (R2). The current flowing from the ADJ pin is typically 50 µA. This ADJ pin contributes to the final VOUT but is usually neglected. Connecting the sense pin to the top of the resistor divider will improve load regulation. Lowering Noise Using the SENSE pin to Kelvin the load will increase accuracy of the output voltage during load regulation. For the fixed voltage devices, adding a capacitor at the GND pin will improve transient response. This capacitor is chosen in the range of 1 µF to 0.1µF and will depend on the amount of output capacitance in the system. PIN DESCRIPTION 1. Sense = Allows Kelvin sense of VOUT at the load. (Positive side of the reference voltage of the device). 2. ADJ = Negative side of the reference voltage for the device. Adding a small bypass capacitor from the ADJ pin to ground will improve the transient response. 3. VOUT = Power output of the device. 4. VCTRL = Supply pin for the control circuitry of the device. The current flow into this pin will be about 1% of the output current. VCTRL must be between 1.0V and 1.3V greater than the output voltage for the device to regulate. 5. VIN = Output load current is supplied through this pin. VIN must be between 0.1V and 0.8V greater than the output voltage for the device to regulate. (4) V CTRL V IN (5) S.O.A V OUT (3) LIMIT SENSE CURRENT LIMIT AMPLIFIER THERMAL OVERLOAD VOLTAGE REGULATION AMPLIFIER V REF SENSE (1) ADJ (2) |
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