SOT-23 for high currents?

[Pina]

Hello,
Let's take a P-Channel MOSFET SI2323DS which is in SOT-23 package. The datasheet states it has 4.7A Id continious and Rdson 0.039 Ohm. I would like to use this transistor to switch 1A load. I know the Rdson is low enough, but the SOT-23 pins are so small that I'm not sure that they can handle such load. So, has anyone ever seen a mosfet in SOT-23 drive such high loads?

David

 

[hakeen]

Hi

4.7A is not DC current, it is pulsed signal (please refer to Note a, at page 2 of datasheet).You have to ensure the power dissipation should not exceed absolute maximum value and result in junction temperature is higher also than 150°C. Unless you dont pass these values, it should be OK.

For the help of calculation of thermal management, you can also utilize thermal model given. It should help.

 

[Pina]

Well, if the thermal consideration is the only thing I should worry about:

P=1A^2 * 0.039 Ohm = 39mW

...giving me 40mW conduction losses (there are practically no switching losses in my application). So, that puts me well withing the standard 300mW allowable power dissipation for SOT-23. I still find it difficult to believe you can put 1A through such a small package :?

Thanks!

 

[frankvh]

You can, and I have. Just be careful with the PCB traces coming into the part - make sure they're thick enough to handle your current without excessive resistance.

 

[FvM]

A rough calculation gives a SOT23 pin and leadframe resistance of about 0.5 mohm. The pin cross section equals a 1.5mm 35u (1 oz) PCB trace.

The main resistance contribution can be expected from the bond wire and the chip itself.

Zetex has SOT23 BJT with a 5A IC,cont spec., they are pretty suited for IGBT gate driver circuits.