RT9167 데이터 시트보기 (PDF) - Richtek Technology

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RT9167

Low-Noise, Fixed Output Voltage, 300mA/500mA LDO Regulator

Richtek Technology 

The value of junction to case thermal resistance θJC is

popular for users. This thermal parameter is convenient

for users to estimate the internal junction operated

temperature of packages while IC operating. It’ s

independent of PCB layout, the surroundings airflow effects

and temperature difference between junction to ambient.

The operated junction temperature can be calculated by

following formula :

TJ = TC + PD x θJC

Where TC is the package case temperature measured by

thermal sensor, PD is the power dissipation defined by

user’ s function and the θJC is the junction to case thermal

resistance provided by IC manufacturer. Therefore it’ s easy

to estimate the junction temperature by any condition.

For example, how to calculate the junction temperature

of RT9167A-28CB SOT-23-5 package? If we use input

voltage VIN = 3.3V at an output current IO = 500mA and

the case temperature (pin 4 of SOT-23-5 package)

TC = 70°C measured by thermal couple while operating,

then our power dissipation is as follows:

PD = (3.3V − 2.8V) x 500mA + 3.3V x 90μA ≅ 250mW

And the junction temperature TJ could be calculated as

following :

TJ = TC + PD x θJC

TJ = 70°C + 0.25W x 130°C/W

= 70°C + 32.5°C

= 102.5°C < TJ(MAX) =125°C

For this operation application, TJ is lower than absolute

maximum operation junction temperature 125°C and it’s

safe to use.

RT9167/A

DS9167/A-26 March 2007

www.richtek.com

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