SPX1580(2000) 데이터 시트보기 (PDF) - Signal Processing Technologies

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SPX1580
(Rev.:2000)

7A Ultra Low Dropout Voltage Regulator Fast Response, Adjustable & Fixed

Signal Processing Technologies 

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.

BLOCK DIAGRAM

(4) VCTRL

S.O.A

VIN (5)

CURRENT

LIMIT

AMPLIFIER

LIMIT

SENSE

THERMAL OVERLOAD

VOLTAGE

REGULATION

AMPLIFIER

VREF

VOUT (3)

SENSE (1)

ADJ (2)

SPX1580

APPLICATIONS NOTES

The SPX1580 is designed as a high performance and low cost

solution for application requiring a lower dropout than

traditional NPN regulators.

The SPX1580 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 3.3V for VIN and 5.0V 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 SPX1580 can power the 2.5V core voltage for

microprocessors such as Pentium, P55C, AMD5k86

and K6 and the IBM PowerPC 603EV and 604EV

processors.

Output Capacitor

An output capacitor for SPX1580 is for circuit compensation

for the device to prevent oscillation. The minimum size of the

output capacitor is either a 330µF Aluminum electrolytic

capacitor or 33µF tantalum. Larger capacitor values improve

the regulator transient response performance and increase

surge load capability. The output capacitor should have an

ESR not more than 280mΩ.

Adjustable Regulator Design

1.25V reference voltage is being developed between the

SENSE pin and the ADJ pin of the SPX1580. 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.

Lowering Noise

Using the SENSE pin to Kelvin the load will increase accuracy

of the output voltage during load regulation. For the fixed

voltage device, adding a bypass capacitor from ADJ pin to

ground improves transient response. A 330pF ceramic

capacitor is recommended.

Rev. 11/21/00

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