REV. 0

ADP3333

–7–

Calculating Junction Temperature

Device power dissipation is calculated as follows:

PV

V

I

V

I

D

IN

OUT

LOAD

IN

GND

=−

()

+

()

device power dissipation is:

P

V

V

mA

V

mA

mW

()

+

()

=

40

30

300

42

20

308

..

.

.

The package used on the ADP3333 has a thermal resistance of

158

°C/W for 4-layer boards. The junction temperature rise

above ambient will be approximately equal to:

TW

C W

C

A

J

=×

°

=

°

0 308

158

48 7

./

.

So, to limit the junction temperature to 125

°C, the maximum

allowable ambient temperature is:

TC

C

C

MAX

A()

..

=° −

° =

°

125

48 7

76 3

Shutdown Mode

Applying a high signal to the shutdown pin, or connecting it to

the input pin, will turn the output ON. Pulling the shutdown

pin to 0.3 V or below, or connecting it to ground, will turn the

output OFF. In shutdown mode, the quiescent current is reduced

to less than 1

µA.

Printed Circuit Board Layout Considerations

Use the following general guidelines when designing printed

circuit boards:

1. Keep the output capacitor as close to the output and ground

pins as possible.

2. Keep the input capacitor as close to the input and ground

pins as possible.

3. PC board traces with larger cross sectional areas will remove

more heat from the ADP3333. For optimum heat transfer,

specify thick copper and use wide traces.

4. Connect the NC pins (Pins 5, 6, and 8) to ground for better

thermal performance.

5. The thermal resistance can be decreased by approximately

10% by adding a few square centimeters of copper area to

the lands connected to the pins of the LDO.

6. Use additional copper layers or planes to reduce the thermal

resistance. Again, connecting the other layers to the ground and

NC pins of the ADP3333 is best, but not necessary. When

connecting the ground pad to other layers use multiple vias.