[Arm-netbook] help needed with a ttl logic circuit

[Luke Kenneth Casson Leighton]

On Mon, Aug 24, 2015 at 6:28 PM, Dominique Dumont <domi.dumont at free.fr> wrote:
> On Monday 24 August 2015 14:19:49 Luke Kenneth Casson Leighton wrote:
>> anyone see any flaws?
>
> It should work.
>
> But I don't see why the first transistor is needed.

 it stops the back-voltage down the 2nd resistor (top right-side,
connected to 3.3V) into the CPU (VREFTTL).  imagine that VREFTTL is
1.8v, and the transistor wasn't there: the *entire CPU* would be
powered from that resistor at well above the CPU's rated voltage.

 with a 28nm CPU, it would be irreversibly damaged by the over-voltage
coming back down that resistor.

 can't have that!

> Well, it's only a few
> cents...

 :)

> All the best
>
> --
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