3

Date: 5/25/04

SPX2808 300mA Low Dropout Voltage Regulator

© Copyright 2004 Sipex Corporation

TYPICAL PERFORMANCE CHARACTERISTICS

Figure 1. Peak Output Current

Figure 2. Minimum Power Dissipation (SOT-89)

800

500

0

INPUT VOLTAGE (V)

200

100

10

20

300

400

30

0

T

T

J

= 85ºC

T

J

= -40ºC

0.0

010 20

40

70 80

AMBIENT TEMPERATURE (ºC)

30

50 60

90

0.4

0.8

1.2

1.6

2.0

The SPX2808 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

only bench testing is the only means to deter-

mine the proper capacitor type and value. The

high quality 100

µF aluminum electrolytic cov-

ers all general application circuits, this stability

can be obtained with a tantalum electrolytic

value of 47

µF.

Another critical point of electrolytic character-

istics is its performance over temperature. The

SPX2808 is designed to operate starting at -

40

°C which may not be true in the case of

electrolytic. Higher temperatures generally no

problem. The electrolytic. type in aluminum

will freeze around -30

°C. This could cause an

oscillation at output of regulator. At a lower

temperature requirement by many applications

the capacitor should maintain its performance.

So as a result, for an application which regulator

junction temperature does not exceed 25

°C, the

output capacitor can be reduced by the factor of

two over the value needed for the entire tem-

perature range.

In most applications the SPX2808 is operating

at few milliamps. In these applications the out-

put 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 100mA. The value decreases with

higher output voltages, since the internal loop

gain is reduced.

The worst case occurs at the lower temperature

and maximum operating currents, the entire

circuit and the electrolytic, should be cooled

down to the minimum temperature. The mini-

mum of 0.6 volts required at the input of regula-

tor above the output to keep the power dissipa-

tion and die heating to its minimum. After the

value for the capacitor has been determined for

actual use, the value should be doubled.

APPLICATION INFORMATION