TK11323BMIL データシートの表示（PDF） - Toko America Inc

部品番号

コンポーネント説明

メーカー

TK11323BMIL

VOLTAGE REGULATOR WITH ON/OFF SWITCH

Toko America Inc  

TK113xxBM/U

DEFINITION AND EXPLANATION OF TECHNICAL TERMS (CONT.)

PACKAGE POWER DISSIPATION (PD)

This is the power dissipation level at which the thermal

sensor is activated. The IC contains an internal thermal

sensor which monitors the junction temperature. When the

junction temperature exceeds the monitor threshold of

150 °C, the IC is shut down. The junction temperature

rises as the difference between the input power (VIN x IIN)

and the output power (VOUT x IOUT) increases. The rate of

temperature rise is greatly affected by the mounting pad

configuration on the PCB, the board material, and the

ambient temperature. When the IC mounting has good

thermal conductivity, the junction temperature will be low

even if the power dissipation is great. When mounted on

the recommended mounting pad, the power dissipation of

the SOT-23L is increased to 600 mW. For operation at

ambient temperatures over 25 °C, the power dissipation of

the SOT-23L device should be derated at 4.8 mW/°C. The

power dissipation of the SOT-89 package is 900 mW when

mounted as recommended. Derate the power dissipation

at 7.2 mW/°C for operation above 25 °C. To determine the

power dissipation for shutdown when mounted, attach the

device on the actual PCB and deliberately increase the

output current (or raise the input voltage) until the thermal

protection circuit is activated. Calculate the power

dissipation of the device by subtracting the output power

from the input power. These measurements should allow

for the ambient temperature of the PCB. The value obtained

from PD /(150 °C - TA) is the derating factor. The PCB

mounting pad should provide maximum thermal

conductivity in order to maintain low device temperatures.

As a general rule, the lower the temperature, the better the

reliability of the device. The thermal resistance when

mounted is expressed 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:

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 usable currents can also be found from the

graph below.

(mW)

3

PD

DPD

6

4

5

25

50

75

150

TA (°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:

IOUT = (DPD / (VIN(MAX) - VOUT)

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

Page 12

April 2000 TOKO, Inc.

Share Link: