TK11227MBX 데이터 시트보기 (PDF) - Toko America Inc

부품명

상세내역

제조사

TK11227MBX

VOLTAGE REGULATOR WITH ON/OFF SWITCH

Toko America Inc  

TK112xx

DEFINITION AND EXPLANATION OF TECHNICAL TERMS (CONT.)

lower the temperature, the better the reliability of the

device. The Thermal resistance when mounted is ex-

pressed as follows:

TJ = 0JA X PD + TA

For Toko ICs, the internal limit for junction temperature is

150 °C. If the ambient temperature, TA is 25 °C, then:

150 °C = 0JA X PD + 25 °C

0JA X PD = 125 °C

0JA = 125 °C/ PD

PD is the value when the thermal sensor is activated. A

simple way to determine PD is to calculate VIN X IIN when

the output side is shorted. Input current gradually falls as

temperature rises. You should use the value when thermal

equilibrium is reached.

The range of currents usable can also be found from the

graph below.

(mW)

3

PD

Dpd

6

4

5

25

50

75

150

T (°C)

Procedure:

1.)

Find PD

2.)

PD1 is taken to be PD X (≈0.8 ~ 0.9)

3.)

Plot PD1 against 25 °C

4.)

Connect PD1 to the point corresponding to the

150 °C with a straight line.

5.) In design, take a vertical line from the maximum

operating temperature (e.g. 75 °C) to the derating

curve.

6.)

Read off the value of PD against the point at which

the vertical line intersects the derating curve. This

is taken as the maximum power dissipation, DPD.

The maximum operating current is IO X (DPD/(VIN(MAX) -

VO).

INPUT/OUTPUT DECOUPLING CAPACITOR CONSIDER-

ATIONS

Voltage regulators require input and output decoupling

capacitors. The required value of these capacitors vary

with application. Capacitors made by different manufactur-

ers can have different characteristics, particularly with

regard to high frequencies and equivalent resistance (ESR)

over temperature. The type of capacitor is also important.

For example, a 5.6 µF aluminum electrolytic may be re-

quired for a certain application. If a tantalum capacitor is

used, a lower value of 3.3 µF would be adequate. It is

important to consider the temperature characteristics of the

decoupling capacitors. While Toko regulators are de-

signed 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 guar-

antee stability. Thus, it is important to consider the charac-

teristics of the capacitor over temperature when selection

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 alumi-

num 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 this value. The recommended minimum capaci-

tance for the TK112xx is 3.3 µF. Please note that linear

regulators with a low dropout voltage have high internal

loop gains which requires care in guarding against oscilla-

tion caused by insufficient decoupling capacitance. The

use of high quality decoupling capacitors suited for your

application will guarantee proper operation of the circuit.

NOISE BYPASS CAPACITOR SECTION

The noise bypass capacitor (CP) should be connected as

close as possible to pin 3 and ground. The recommended

value for CP 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 CP is not

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

Page 18

1-3-96

January, 1996 TOKO, Inc.

Share Link: