Apptech wrote:
> At $US10 in 5000 quantity from Digikey it's a bit dearer [tm] in 
> component cost than a discrete solution. Component cost is far from 
> the only consideration, but $10 goes a longway on such things
> But, a nice solution where raw cost is not too important.
>
>         http://www.national.com/ds/LM/LMD18200.pdf
>   
I'm using it in a situation where a high-accuracy timing source (1 PPS, 
+- 1 uS or so) is needed, and must be provided to the equipment by 
putting a 120us hole in the supply every second.  Because of the 1uS 
"jitter" requirement, I have to drive the power line not only high but 
also low to drain off any power left over in the cable capacitance...  
so I need both high side and low side drivers, and all the circuitry to 
prevent shoot-through and the like.  Plus, I need short circuit and 
thermal overload shutdown since these faults can and do occur.

Each LMD18200 gains me two "channels"..  I.E. two complete high side/low 
side pairs...  which can be used to drive two pieces of equipment.   I 
use a total of 2 of the LMD18200's in each of these particular units.  
It also has all of the short-circuit and thermal overload protection 
built in.   I would love to find an alternative which was less expensive 
and similar in reliability but haven't found such an option.  

If you've got a suggestion for a driver set which will do such a thing 
(Drive a pair of fets in a "totem pole" configuration, 24VDC, <1us or so 
propagation time for turn off, short circuit and/overload protection 
(while still permitting inrush), and so on)...  please let me know.

I've been through dozens of parts and originally ended up with the 
L6202's with the first revision of this product (they had adequate 
relaibility) and then tried the L6206'es (both with integrated drivers) 
hoping they were more reliable (they were not), and then tried to find 
an appropriate discrete solution, but ended up with the LMD18200 since 
it was actually the cheapest solution I could find when I factored in 
the cost of placing the components and which I couldn't blow up by short 
circuiting the output and/or putting enough load through it to send it 
into thermal runaway.   In fact, I'm not sure I've ever destroyed a 
LMD18200.

But like I said, I would love to find something cheaper..   $10 each 
(they are just under $11 at Qty 100) is a bit expensive...  but when you 
figure out that they contain two high-side fets, two low-side fets, all 
the driver circuitry (minus a few caps), and thermal and short-circuit 
protection, it sure seems like a reasonable price to me.

-forrest
 
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