AS1582
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.
4.
V
V
OUT = Power output of the device.
CTRL = 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.
BLOCK DIAGRAM
(4) VCTRL
VIN (5)
S.O.A
CURRENT
LIMIT
LIMIT
AMPLIFIER
VOUT (3)
SENSE (1)
ADJ (2)
SENSE
THERMAL OVERLOAD
VOLTAGE
REGULATION
AMPLIFIER
VREF
APPLICATIONS NOTES
The AS1582 is designed as a high performance and low cost
solution for application requiring a lower dropout than
traditional NPN regulators.
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 50µA. 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.
The AS1582 uses a separate input voltage VCTRL (VCTRL
≥
V
OUT+ 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.
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 1µF to 0.1µF 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 = VOUT / VIN).
Rev. 10/2/00
SIPEX [ SIPEX CORPORATION ]
