TK11922M データシートの表示（PDF） - Toko America Inc

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TK11922M

VOLTAGE REGULATOR WITH RESET OUTPUT

Toko America Inc  

TK119xx

APPLICATION INFORMATION

INPUT/OUTPUT DECOUPLING CAPACITOR

CONSIDERATIONS

Voltage regulators require input and output decoupling

capacitors. The required values of these capacitors vary

with application. Capacitors made by different

manufacturers can have different characteristics,

particularly with regard to high frequencies and Equivalent

Series Resistance (ESR) over temperature. The type of

capacitor is also important. For example, a 4.7 µF aluminum

electrolytic may be required for a certain application. If a

tantalum capacitor is used, a lower value of 2.2 µF would

be adequate. It is important to consider the temperature

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 temperature.

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

capacitance is required to guarantee stability. Thus, it is

important to consider the characteristics of the capacitor

over temperature 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 particular application. After taking thermal

characteristics and tolerance into account, the minimum

capacitance value should be approximately two times the

value. The recommended minimum capacitance for the

TK119xx is 2.2 µF for a tantalum 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 capacitance. The use of high

quality decoupling capacitors suited for your application

will guarantee proper operation of the circuit.

BOARD LAYOUT

Copper pattern should be as large as possible. Power

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

ESR capacitor is recommended. For low temperature

operation, select a capacitor with a low ESR at the lowest

operating temperature to prevent oscillation, degradation

of ripple rejection and increase in noise. The minimum

recommended capacitance is 2.2 µF.

VIN

GND

VOUT

+

+

GND

RESET

CONTROL

SOT-23L BOARD LAYOUT

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 µF. 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.

RESET OUTPUT CONSIDERATIONS

It is important to note the accuracy of the regulator and

voltage detector functions when they are combined within

one IC. The figure below illustrates the voltage regulator

and voltage detector implemented with individual reference

voltages.

VMAX

VMIN

RMAX

RMIN

NON-TOKO APPROACH

January 1999 TOKO, Inc.

Page 21

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