Re: Paralleling FETS

On Wed, 15 Oct 2008 06:51:43 -0400, Hammy <spamme@xxxxxxxxxxx> wrote:



I'm thinking of using a dual mosfet in a SC-88 package (NTJD4401N), in
a current source.

The FET's will be controlled by an LMV611 opamp. They don't state in
the data*** how well matched the pair is (threshold voltage and
Rdson).

I read a note from TI on paralleling FETS and it said that process
variations for Vt and Rdson for single FETS same production batch were
nowhere near the worst case data*** specs.

Is it a good idea to use Dual FETS like that?

http://www.onsemi.com/pub_link/Collateral/NTJD4401N-D.PDF

We've found big mismatches, like a volt of Vg, in discrete fets, all
from the same batch. Best to close a loop around each fet, or use big
source resistors.

John

.

Quantcast