Jinx wrote:
> As I understand it L6206 output -> delay -> enable pin
That's basically it... 
> How about an RC on the base of a FET/UJT/BPT or logic gate (perhaps a Schmitt eg 7414 or 4093)
>   
That's basically how the L6206 works today.

There is an OCD output which is an open collector FET with about 40 ohms 
of Rdson.   There is also the EN pin which is internally schmitt triggered.

Normally the OCD and EN pins are tied together and an R/C pair is tied 
to this node.  R to VCC, C to ground.   When an OCD occurs (threshold 
set by another resistor), the internal OCD FET turns on and drains the 
capacitor.  Depending on the size of the capacitor, you have somewhere 
between 1 and 10us before the capacitor voltage reaches the negative 
going threshold and the load is turned off.   At this point, you are no 
longer in overcurrent, so the OCD fet turns off and the capacitor starts 
to charge through the resistor.  Depending on the R/C values, you then 
have somewhere around 100-1000us before the capacitor charges to the 
positive going threshold and the load turns back on.

Since the C value is what controls the off-delay, I have attempted to 
increase this to the point where the delay is longer than the inrush.  
This works to solve the inrush problem, but effectively disables the 
short circuit protection, since the L6206 heats internally every cycle - 
and the off time is not sufficiently long to allow the chip to cool 
between tries.  After a few seconds, a short will take out the L6206, 
causing the smoke to be released.    Increasing the R value does help a 
bit, but only prolongs the agony, since it doesn't seem that you can 
increase the R value to a point where it is large enough that the 
off-time will permit the chip to cool.

I'm pretty convinced the solution lies in the digital realm.   I will 
probably try with a 12F - and perhaps something from Atmel, although I 
don't have any AVR tools here at all.   What I am hoping is that someone 
will say, "oh yeah, there's this cool little 8 pin CPLD from Magical 
Semiconductor with like 10,000 gates, an internal oscillator, and only 
costs 25 cents in qty", or even "If you can live with 14 pins, there's a 
new PIC you might not be aware of with a 8mhz intosc and a 5xPLL which 
should make your life easier".   My problem is that I'm really dealing 
with something which means you have to recognize the OCD output, delay, 
and then turn off the EN pin, all within the execution time of something 
like 20 instructions on an 8Mhz PIC.

-forrest

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