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6 Excellence in Analog Power Products A S 1 5 8 1

5A Ultra Low Dropout Voltage Regulator Fast Response, Adjustable & Fixed FEATURES APPLICATIONS * Low Dropout Voltage 500mV at 5A Full Load Current ¢3.3V to 2.8V ATX Power Supplies ¢ Adjustable Output Down to 1.2V from ATX Power Supply ¢ 3.3V to 2.9V for Portable PENTIUM™ Processor ¢ Fixed Output Voltages of 3.3V, 2.8V & 2.5V SV to 3.5V VRE Supply ¢ Extremely Tight Voltage and Line Regulation © High Efficiency “Green” Computer Systems Standard 5-Terminal Low Cost TO-220 & TO-263 PRODUCT DESCRIPTION The Alpha Semiconductor AS1581 is a 5A Low Dropout Regulator with extremely low dropout voltage. The adjustable version requires only two external resistors to set the output voltage. The fixed version has a preset output of 3.3V, 2.8V or 2.5V and does not require any external resistors. The AS1581 features a low dropout of less than 400mV(typ.) and offers fast transient response. This device is suitable for Pentium applications requiring 2.8V or 2.5V from 3.3V ATX power supplies, where a low current input voltage 1V greater than the output voltage is needed. With an external sense pin the load regulation is less than ImV. This device is an excellent choice for the use in powering low voltage microprocessors that require a lower dropout, fast transient response to regulate from 3.3V and SV supplies. The AS1581 is also an excellent choice as a post regulator for switching supplies applications. The AS1581 offers full protection against over-current faults, reversed input polarity, over temperature operation and positive and negative transient voltage. The AS1581 is offered in a 5 pin TO-220 and TO-263 compatible with industry standard 5-terminal regulators. For 7A, 3A and. 1.5A ultra low dropout versions refer to AS1580, AS1582 and AS1583 data sheets respectively.

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AS1581U AS1581T Adjustable AS1581U-X ‘Consult with Tactory for other fixed output vollages PIN CONNECTIONS X= Output Voltage 3.3V, 28V & 2.5V) ASIS81 L. SENSE ALPHA | 2.ADI or FIXED 12345 ; ADE or EIXED ASIS81 3. Vour our 12345] 4Vau, HHHHH 4 Yer sv QOUUU + Top View Front View Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1390 Fax: (925) 417-1391 Rev.8/27/99

Operating Junction Temperature Range ELECTRICAL CHARACTERISTICS at Vs=14V, Ta=25°C, lo=10mA, C2=100uF, unless otherwise specified. (Note 1) (Boldface applies over full temperature range). Parameters Conditions ASI581 Units Min Typ Max To=10mA to 5A 2.400 2.600 ‘Output Voltage Verni=6.3V t0 12V, Vin=3.3V to 12V, Io=10mA, 2744 2.800 2.856 V Jo=10mA to 5A 2.688 2.912 ‘Output Voltage Verni=6.3V 10 12V, Vin=3.3V 10 12V, Io=10mA, 3234 3.300 3.366 v Io=10mA to 5A 3.168 3.462 All Voltage Options Reference Voltage Vermi=2.75V, Vin=2.00V, Io=10mA 1238 1250 1263 Vv Verai=2.7V to 12V, Vix=2.05V to 5.5V, Io=10mA to 5A Line Regulation Verni=2.5V 00 12V, Vins L75V 10 5.5V, [o=10mA. Vars=0V 1.0 3.0 mV Dropout Voltage Minimum Verau(Note2) | Van=0V 1.10 1.25 v (Vera — Vour) Viy=2.05V, I= 1A. Dropout Voltage Minimum Viy(Note2) Vap=0V 0.40 0.50 Vv (Vev- Vour) Vin=2.75V, Io=5A ew lee “Thermal Regulation 30ms Pulse | 0.002 Ripple Rejection Vori=3.75V Vin=3.15V, [o=2.5A,Van=0V 60 80 T=25, Vauern=1Vpp at 120Hz Control Pin Current Vapi=0V 60 120 Vern =2.75V, Vin=2.05V, lo=5A mA ‘Adjustable Pin Current Verri=2.75V, Vin=2.05V,Van=0V Ip=10mA ee ee ee ee “Thermal Resistance TO-2205 Junction to Case (ic) ee ee ee ee a a The Bold specifications applying to the over full operating temperature range. Note 1: Low duty cycle pulse testing with Kelvin connections are required to order to maintain accurate data. Note 2: Dropout voltage is defined as the minimum differential between Vy and Vour or Verer and Vourrequired to maintain regulation at Vour 99% Nominal Vour. Note 3: Veer is measured across the Adjust pin to Sense pin. Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1390 Fax: (925) 417-1391 Rev.8/27/99

  1. Sense = Allows Kelvin sense of Vour at the load. (Positive side of the reference voltage of the device). 1. 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. 1. Vour= Power output of the device. 4. Verri= Supply pin for the control circuitry of the device. The current flow into this pin will be about 1% of the output current. Vcrr_ must be between 1.0V and 1.3V greater than the output voltage for the device to regulate. 4, Vix= Output load current is supplied through this pin. Vv must be between 0.1V and 0.8V greater than the output voltage for the device to regulate. BLOCK DIAGRAM Vom. © © Vy 3) Kc [S04 | uRRENT caw ANPLIFIER © Vou @) SENSE © SENSE (1) VOLTAGE REGULATION AMPLIFIER I Veer © ADI @) APPLICATIONS NOTES The AS1581 is designed as a high performance and low cost Adjustable Regulator Design solution for application requiring a lower dropout than 1.25V reference voltage is being developed between the traditional NPN regulators. SENSE pin and the ADJ pin of the AS1581. Adding two The AS1581 uses a separate input voltage Vere. (Vere 2 external resistors (see fig 1.) will allow setting the output Vourt 1.3V) to minimize the dropout voltage. This allows voltage from 1.25V to 6V. R, is chosen so that this current is the 2.5V power for the load to come from a 3.3V system specified minimum load current of 10mA. R, is given by the supply. As added benefit this will reduce the heat dissipation, formula: Vour = Vrer (1+ R2/R:) + Taps (Ro). The current and lower heatsink and cooling fan cost. A_ typical flowing from the ADJ pin is typically 504A. This ADJ pin application would use 5V for Vin and 3.3V for Vere from a contributes to the final VOUT but is usually neglected. motherboard power supply to provide a nominal 2.5V output. Connecting the sense pin to the top of the resistor divider will Using the sense pin allows to Kelvin measure the output, improve load regulation. reducing resistive-associated errors. The AS1581 can power the 2.5V core voltage for Lowering Noise microprocessors such as Pentium™, PSSC™, AMDSk86™ Using the SENSE pin to Kelvin the load will increase and K6™ and the IBM PowerPC™ 603EV and 604EV accuracy of the output voltage during load regulation. For the processors. fixed voltage devices, adding a capacitor at the GND pin will improve transient response. This capacitor is chosen in the range of 1F to 0.1F and will depend on the amount of output capacitance in the system. *The reduction of heat dissipation is a result of the increase of the regulator efficiency (efficiency = Vour/ Vix). Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1390 Fax: (925) 417-1391 Rev.8/27/99

Fig. | Adjustable Regulator cl ALPHA | Vour sv 330uF ASISBI Vera. © RL 2X 330uF 1249 (DV cri tecded when V ,<5V. 2) Vour® V gep(l +R RD+T yp) R2. (3) V gepis measured across adjust to sense, Fig.2 Typical Fixed Regulator 33V Vw e ‘s Noor 0 ALPHA T™ %or cL Re “ a | Von. © Vv, CR ‘SENSE GND Q a 10uP 2X 330uF (1) Venu. is needed when Viv <SV. Alpha Semiconductor Inc. 1031 Serpentine Lane. Pleasanton, CA 94566 Tel: (925) 417-1391 Fax: (925) 417-1390 Rev 8/27/99