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AS1582
3A Ultra Low Dropout Voltage Regulator Fast Response, Adjustable & Fixed
FEATURES
* Low Dropout Voltage 500mV at 3A Full Load Current * Fixed Output Voltages of 3.3V, 2.8V & 2.5V * Adjustable Output Down to 1.2V from ATX Power Supply * Extremely Tight Voltage and Line Regulation * Standard 5-Terminal Low Cost TO-220 & TO-263
APPLICATIONS
* 3.3V to 2.8V ATX Power Supplies * 3.3V to 2.9V for Portable PENTIUM Processor * 5V to 3.5V VRE Supply * High Efficiency "Green" Computer Systems
PRODUCT DESCRIPTION
The AS1582 is a 3A 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 AS1582 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 1mV. 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 5V supplies. The AS1582 is also an excellent choice as a post regulator for switching supplies applications. The AS1582 offers full protection against over-current faults, reversed input polarity, over temperature operation and positive and negative transient voltage. The AS1582 is offered in a 5 pin TO-220 and TO-263 compatible with industry standard 5-terminal regulators. For 7A, 5A and 1.5A ultra low dropout versions refer to AS1580, AS1581 and AS1583 data sheets respectively.
ORDERING INFORMATION
TO-22O 5-PIN AS1582U AS1582U-X TO-263 5-PIN AS1582T AS1582T-X OUTPUT Adjustable Fixed
Consult with factory for other fixed output voltages. X= Output Voltage (3.3V, 2.8V or 2.5V)
PIN CONNECTIONS
TO-263-5 (T)
TO-220-5 (U)
AS1582
12345
1. 2. 3. 4. 5.
SENSE ADJ or FIXED VOUT VCTRL VIN
AS1582
1 2 345
1. SENSE 2. ADJ or FIXED 3. V OUT 4. V CTRL 5. V IN
Top View
Front View
Rev. 10/2/00
AS1582
ABSOLUTE MAXIMUM RATINGS
Power Dissipation.................................................... Internally Limited Lead Temp (soldering, 10 seconds)........................................... 300C Storage Temperature Range ...................................... -65C to +150C Operating Junction Temperature Range AS1582 Control Section................................................0C to +125C AS1582 Power Transistor .............................................0C to +150C Input Supply Voltage ..........................................................6V VCTRL Input Voltage ..........................................................13V
ELECTRICAL CHARACTERISTICS at VS =14V, Ta=25C, Io=10mA, C2=100F, unless otherwise specified. (Note 1)
(Boldface applies over full temperature range).
Parameters 2.5V Version Output Voltage VCTRL=6.0V to 12V, VIN=3.0V to 5.0V, IO=10mA IO=10mA to 3A VCTRL=6.3V to 12V, VIN=3.3V to 12V, IO=10mA IO=10mA to 3A VCTRL=6.3V to 12V, VIN=3.3V to 12V, IO=10mA IO=10mA to 3A VCTRL=2.75V, VIN=2.00V, IO=10mA VCTRL=2.7V to 12V, VIN=2.05V to 5.5V, IO=10mA to 3A VCTRL=2.5V to 12V, VIN=1.75V to 5.5V, IO=10mA VADJ=0V VCTRL=2.75V, VIN=2.1V, IO=10mA to 3A,VADJ=0V VADJ=0V VIN=2.05V, IO=1A VADJ=0V VIN=2.75V, IO=3A VCTRL=2.75V, VIN=2.05V,dVO=100mV,VADJ=0V VCTRL=5V, VIN=3.3V,VADJ=0V 30ms Pulse VCTRL=3.75V VIN=3.75V, IO=2.3A,VADJ=0V TJ=25, VRIPPLE=1Vpp at 120Hz VADJ=0V VCTRL =2.75V, VIN=2.05V, IO=3A VCTRL=2.75V, VIN=2.05V,VADJ=0V IO=10mA TO-220-5 Junction to Case (JC) Junction to Ambient (JA) Junction to Case (JC) Junction to Ambient (JA) 60 3.1 5 0.002 80 60 50 120 120 3 50 3 60 mA A C/W C/W C/W C/W 10 0.02 2.450 2.400 2.500 2.550 2.600 V Conditions Min AS1582 Typ Units Max
2.8V Version Output Voltage 2.744 2.688 2.800 2.856 2.912 V
3.3V Version Output Voltage All Voltage Options Reference Voltage 1.238 1.250 1.263 V 3.234 3.168 3.300 3.366 3.432 V
Line Regulation Load Regulation (Note1) Dropout Voltage Minimum VCTRL (Note2) (VCTRL - VOUT) Dropout Voltage Minimum VIN(Note2) (VIN - VOUT) Current Limit Minimum Load Current Thermal Regulation Ripple Rejection Control Pin Current Adjustable Pin Current Thermal Resistance
1.0 1.0 1.05 0.40
3.0 5.0 1.18 0.50
mV mV V V A mA %W dB
TO-263-5
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 VIN and VOUT or VCTRL and VOUT required to maintain regulation at VOUT 99% Nominal VOUT. Note 3: VREF is measured across Adjust pin to Sense pin.
Rev. 10/2/00
AS1582
PIN DESCRIPTION
1. 2. 3. 4. 5. Sense = Allows Kelvin sense of VOUT at the load. (Positive side of the reference voltage of the device). 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. VOUT = Power output of the device. 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. 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.
BLOCK DIAGRAM
(4) VCTRL S.O.A VIN (5)
CURRENT LIMIT AMPLIFIER
LIMIT SENSE VOUT (3)
THERMAL OVERLOAD SENSE (1) VOLTAGE REGULATION AMPLIFIER
VREF
ADJ (2)
APPLICATIONS NOTES
The AS1582 is designed as a high performance and low cost solution for application requiring a lower dropout than traditional NPN regulators. The AS1582 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 AS1582 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 AS1582. 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 50A. 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 1F to 0.1F and will depend on the amount of output capacitance in the system.
Rev. 10/2/00
AS1582
TYPICAL APPLICATION
Fig. 1 Adjustable Regulator
3.3V VIN 5V VCTRL C1 330uF
VIN
VOUT
AS1582
VCTRL ADJ C2 10uF
2.5V VOUT
SENSE
R1 124 C4 2 X 330uF
C3 .033uF
R2 124
(1) V CTRL needed when VIN < 5V. (2) V OUT = V REF (1 + R2/ R1) + I ADJ R2. (3) V REF is measured across adjust to sense.
Fig.2 Typical Fixed Regulator
3.3V VIN C1 5V VCTRL
330uF
VIN
VOUT
AS1582
2.5V VOUT
VCTRL GND C2 10uF
SENSE
C4 2 X 330uF
(1) VCTRL is needed when VIN <5V.
Rev. 10/2/00

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