PAM3101AAA310 datasheet(13/26 Pages) PAM

13 / 26 page

Thermal considerations

based on the standard JEDEC 51-3 for a single-

layer thermal test board, the maximum power

dissipation at T =25°C can be calculated by

Thermal protection limits power dissipation in the

PA M 3 1 0 1 . W h e n t h e j u n c t i o n t e m p e r a t u r e

following formula:

exceeds 150°C, the OTP (Over Temperature

Protection) starts the thermal shutdown and turns

= (125°C-25°C)/250=0.4W

SOT-23

D(MAX)

the pass transistor off. The pass transistor

= (125°C-25°C)/180=0.55W

SOT-89

D(MAX)

resumes operation after the junction temperature

drops below 120°C.

It is also useful to calculate the junction

temperature of the PAM3101 under a set of

F o r c o n t i n u o u s o p e r a t i o n , t h e j u n c t i o n

specific conditions. For example, suppose the

temperature should be maintained below 125°C.

input voltage V =3.3V, the output current

I N

The power dissipation is defined as:

I =300mA and the case temperature T =40°C

measured by a thermalcouple during operation,

P = (V -V

)*I +V *I

OUT

GND

the power dissipation for the Vo=2.8V version of

the PAM3101 can be calculated as:

The maximum power dissipation depends on the

thermal resistance of IC package, PCB layout,

P =(3.3V-2.8V)*300mA+3.3V*70μA≌150mW

the rate of surrounding airflow and temperature

difference between junction and ambient. The

And the junction temperature, T , can be

maximum power dissipation can be calculated by

calculated as follows:

the following formula:

T = T +P *θ

= (T

-T )/θ

D(MAX)

J(MAX)

T = 40°C+0.15W*250°C/W

=40°C+37.5°C

Where T

is the maximum allowable junction

J(MAX)

=77.5°C<T

= 125°C

J(MAX)

temperature 125°C, T is the ambient temperature

and θ

is the thermal resistance from the junction

For this operating condition, T is lower than the

to the ambient.

a b s o l u t e

m a x i m u m

o p e r a t i n g

j u n c t i o n

temperature, 125°C, so it is safe to use the

For example, as θ

is 250°C/W for the SOT-23

PAM3101 in this configuration.

package and 180°C/W for the SOT-89 package

Power Analog Microelectronics, Inc

www.poweranalog.com

PAM3101

300mA High PSRR Low Dropout CMOS Linear Regulator

11/2010 Rev 2.5

PAM3101AAA310 Datasheet(PDF) 13 Page - Power Analog Micoelectronics

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