Re: Wimpy Comparator Open Collector/Drain Current



On May 19, 5:00 pm, Joerg <notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx>
wrote:
D from BC wrote:
I want to discharge a mosfet gate really fast!
Cg~2nF at worst.
Vg=12V

I'd like to have a open collector/open drain output comparator do the
job.

For example.

The LMV393 open collector sink output acts like a 12 ohm resistor..
The graph stops at 50mA sink..

The LMV7235 open drain levels off at 60mA @ a Vlow of 2V!!!
Built in current limit?
Wtf? There are mosfets with milliohm conduction...Why not put'm in the
comparator..

Is it safe to assume all common comparators have wimpy internal open
collector/drain output transistors?

Can I get a 12 amp spike!! :) Arrrffff Arrrfff...

I suspect I'll have to resort an external transistor to short out the
charge.

That's how I do those things. A BSS123 or 2N7002 can drain the gate
capacitance really fast. But mind its max peak current. You can always
use more than one. Sure beats finding that expensive boutique comparator
and then the purchasing department can't get them anymore some day.

On a normal open collector comparitor, a PNP is often a better way to
go if fast pull down is needed. You don't have to wait while the pull
up charges the gate of a MOSFET.

.



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