[Cryptech Tech] Alpha Avalanche Noise Block

[Fredrik Thulin]

On Friday, April 10, 2015 11:31:08 PM Павел Шатов wrote:
> On 10.04.2015 16:11, Fredrik Thulin wrote:
> > On Friday, April 10, 2015 01:07:21 PM Павел Шатов wrote:
> >> Hello!
> >> 
> >> Fredrik, I've attached my variant of power supply regulator for an
> >> updated version of avalanche noise block. It will output stable +12V
> >> with input voltage starting from around +7V and up to +18V. If +12V is
> >> not enough, you can increase value of R1 to trim output voltage. It
> >> would be great if you could update schematics when you have time.
> > 
> > Great, thank you. I'm planning on doing some Cryptech catch up this
> > weekend.
> > 
> > Would it be possible to lower the required input voltage to +5v? That way
> > I
> > could use this same circuit with my USB based test units.
> 
> Yes, it is possible. This regulator can operate from +2.8V, so +5V is
> fine. One feature of this regulator is programmable under-voltage
> lockout. It is controlled by resistor R4. In my circuit I've set
> under-voltage threshold at +6V using R4=33k. If you want nominal input
> voltage to be +5V, then you can set under-voltage threshold to say +4V
> with R4=18k. There's a formula in the datasheet, that you can use to
> calculate R4 value given desired under-voltage threshold. If you don't
> need this under-voltage lockout feature during your experiments, you can
> disable it altogether by shorting out R4.

This weekend turned into Monday morning.

I looked at the SEPIC converter you suggest (LTM8045EY) and thought maybe we 
need to talk about that choice a bit more. It is fairly expensive (Farnell US 
has it at $12.27 in single quantities) and while that may be acceptable at 
this point (having stable HIGH_V is also of course important to us) it also 
seems to only be available in BGA package?

I think that is worse, since it means we can't really test it before getting 
the Alpha boards manufactured, and also can't use it in simpler units. How did 
you choose that exact part? Could we reasonably find another SEPIC converter 
with good enough vcc-noise properties but another package?

Anyway, I just updated the schematics on the wiki with the Schmitt trigger.

/Fredrik