TK11900M Ver la hoja de datos (PDF) - Toko America Inc

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TK11900M

ADJUSTABLE LOW DROPOUT REGULATOR

Toko America Inc  

TK11900

APPLICATION INFORMATION

BOARD LAYOUT

Copper pattern should be as large as possible. Power

dissipation is 400 mW for the SOT-23L package. A low

Equivalent Series Resistance (ESR) capacitor is recom-

mended. For low temperature operation, select a capacitor

with a low ESR at the lowest operating temperature to

prevent oscillation, degradation of ripple rejection and in-

crease in noise. The minimum recommended capacitance

is 2.2 µF.

VIN

GND

VOUT

+

+

to consider the characteristics of the capacitor over tem-

perature when selecting decoupling capacitors.

The ESR is another important parameter. The ESR will

increase with temperature but low ESR capacitors are often

larger and more costly. In general, tantalum capacitors offer

lower ESR than aluminum electrolytic, but new low ESR

aluminum electrolytic capacitors are now available from

several manufacturers. Usually a bench test is sufficient to

determine the minimum capacitance required for a particu-

lar application. After taking thermal characteristics and

tolerance into account, the minimum capacitance value

should capacitor or 3.3 µF for an aluminum electrolytic.

Please note that linear regulators with a low dropout voltage

have high internal loop gains which require care in guarding

against oscillation caused by insufficient decoupling ca-

pacitance. The use of high quality decoupling capacitors

suited for your application will guarantee proper operation of

the circuit.

GND

NOISE BYPASS

CONTROL

FEEDBACK

SOT-23L BOARD LAYOUT

INPUT/OUTPUT DECOUPLING CAPACITOR CONSID-

ERATIONS

Voltage regulators require input and output decoupling

capacitors. The required values of these capacitors vary

with application. Capacitors made by different manufactur-

ers can have different characteristics, particularly with

regard to high frequencies and ESR over temperature. The

type of capacitor is also important. For example, a 4.7 µF

aluminum electrolytic may be required for a certain applica-

tion. If a tantalum capacitor is used, a lower value of 2.2 µF

would be adequate. It is important to consider the tempera-

ture characteristics of the decoupling capacitors. While

Toko regulators are designed to operate as low as -30 °C,

many capacitors will not operate properly at this tempera-

ture. The capacitance of aluminum electrolytic capacitors

may decrease to 0 at low temperatures. This may cause

oscillation on the output of the regulator since some capaci-

tance is required to guarantee stability. Thus, it is important

Page 8

NOISE BYPASS CAPACITOR SECTION

The noise bypass capacitor (CN) should be connected as

close as possible to pin 1 and ground. The recommended

value for CN is 0.01 mF. The noise bypass terminal has a

high impedance and care should be taken if the noise

bypass capacitor is not used. This terminal is susceptible

to external noise, and oscillation can occur when CN is not

used and the solder pad for this pin is too large.

OUTPUT VOLTAGE SETTING

The output voltage can be set from 1.5 to 15 V by two

external resistors according to the following equation:

VOUT = 1.25 V x [(R1 + R2) / R2]

VOUT

R1

FEEDBACK

R2

where 10 kΩ - R2 - 60 k

November 2000 TOKO, Inc.

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