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SPX2931U

100mA Low Dropout Voltage Regulator

Signal Processing Technologies 

Application Hints

The SPX2931 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 determine the proper capacitor

type and value. The high quality 100 µF aluminum

electrolytic covers all general application circuits, this stability

can be obtained with a tantalum electrolytic value of 47 µF.

Another critical point of electrolytic characteristics is its

performance over temperature. The SPX2931 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

SPX2931

factor of two over the value needed for the entire

temperature range.

Other points with linear regulators is that the twitch higher

output current stability decreases. In most applications the

SPX2931 is operating 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 100 mA.

With the SPX2931 adjustable regulator, the minimum value

of output capacitance is a function of the output voltage.

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 minimum of 0.6 volts required at the input

of regulator above the output to keep the power dissipation

and die heating to its minimum. After the value for the

capacitor has been determined for actual use, the value

should be doubled.

Rev. 10/24/00

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