SPX8863 데이터 시트보기 (PDF) - Signal Processing Technologies

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SPX8863

120 mA, Low Dropout Voltage Regulator (Preliminary Information)

Signal Processing Technologies 

Application Hints

The SPX8863 requires an output capacitor for device stability.

The value required varies greatly depending upon the

application circuit and other factors. The high frequency

characteristics of electrolytic capacitors depend greatly on the

type and also on the manufacturer. Sometimes bench testing is

the only means to determine the proper capacitor type and

value. The high quality 2.2µF aluminum electrolytic capacitor

covers all general application circuits, this stability can be

obtained with a tantalum electrolytic value of 1µF.

SPX8863

In general, linear regulator stability decreases with higher

output currents. In some applications the SPX8863 may

operate at few milliamps. In these applications the output

capacitance can be further reduced. For example, when the

regulator is running at 10mA output current the output

capacitance value is half compared to the same regulator

that is running at 150mA.

With the SPX8863 adjustable regulator, the minimum value

of output capacitance is a function of the output voltage.

The value decreases with higher output voltages, since the

closed loop gain is increased.

Typical Applications Circuits

The SPX8863 provides access to the internal reference. A 10µF capacitor on the BYP pin will provide a significant reduction in

output noise. This pin may be left unconnected if the output noise is not a major concern. The SPX8863 start-up speed is inversely

proportional to the size of its capacitor. Applications requiring a slow ramp-up of output voltage should consider larger values of

CBYP. If the rapid turn-ON is necessary, omit bypass capacitor.

Figure 1 shows SPX8863 standard application circuit. The EN (enable) pin is pulled high (>2.0V) to enable the regulator. To disable

the regulator, EN < 0.6V.

VIN

+ GND

EN

3

4

2

SPX8863

1

+

5 BYP

(Optn)

VOUT

Hi-ON

Lo-OFF

Top View

Fig. 1

The SPX8863 in figure 2 shows adjustable output voltage configuration. Two resistors set the output voltage. The formula for output

voltage is:

VOUT = 1.235V x (1+ R1)

R2

Resistor values are not critical as the Adj. pin has high input impedance, for best results use resistors of 47kΩ or less. A capacitor for

Adj to ground will provide improved noise performance.

VIN

+ GND

EN

Hi-ON

Lo-OFF

3

4

VOUT

2

+

SPX8863

1

5 ADJ

R1

Byp

R2

(Optn)

Top View

Fig. 2

Rev. 10/24/00

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