LP2967 datasheet(13/17 Pages) NSC

13 / 17 page

Application Hints

EXTERNAL CAPACITORS

The LP2967 low dropout regulator requires two external

capacitors, C

IN and COUT to assure the device’s output

stability. C

BYPASS may be used to reduce output noise. The

capacitors must be correctly selected with respect to capaci-

tance values for all three capacitors and ESR value for

OUT.

Input Capacitor

An input capacitor with a minimum capacitance value of 1µF

is required between the LP2967 input and ground (the

amount of capacitance may be increased without limit). This

capacitor must be located a distance of not more than 0.5

inches from the input pin and returned to a clean analog

ground. Any good quality ceramic or tantalum may be used

for this capacitor.

Output Capacitor

The output capacitor must meet the requirement for mini-

mum capacitance value of 2.2 µF and also have an appro-

priate ESR (equivalent series resistance) value. The LP2967

is actually designed to work with ceramic or tantalum output

capacitors, utilizing circuitry which allows the regulator to be

stable with an output capacitor whose ESR is as low as 4

Ω. It may also be possible to use a film capacitor at the

output, but this type is not as attractive for reasons of size

and cost.

Important: The output capacitor must maintain its ESR in

the stable region over the full operating temperature range of

the application to assure stability. The minimum required

amount of output capacitance is 2.2 µF. Output capacitor

size can be increased without limit. It is important to remem-

ber that capacitor tolerance and variation with temperature

must be taken into consideration when selecting an output

capacitor so that the minimum required amount of output

capacitance is provided over the full operating temperature

range.

LP2967-3.3V Region of Stability with 10 µF C

OUT

10114208

LP2967-3.3V Region of Stability with 4.7 µF C

OUT

10114207

LP2967-2.5V Region Of Stability with 10 µF C

OUT

10114209

LP2967-2.5V Region Of Stability with 4.7 µF C

OUT

10114210

LP2967 Datasheet(PDF) 13 Page - National Semiconductor (TI)

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