[Cryptech Tech] Alpha Avalanche Noise Block

[Павел Шатов]

On 13.04.2015 9:55, Fredrik Thulin wrote:
> 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?

Fredrik, excuse me, I don't understand what simpler units you are 
referring to. Alpha board is not going to be simple, it is going to be 
complex. Our CPU and FPGA and RAM are all BGAs. If we can't avoid BGAs, 
let's use them to our advantage then. Alpha is not going to be cheap, 
because Artix-7 200T costs about $300. Because of that, I didn't think 
that $12 power regulator was like very expensive.

Two-layer boards that you can etch and solder yourself are one story, 
Alpha board is going to be completely different story. I don't think 
that it is appropriate to pick same components for different types of 
boards. If you need some regulator for you experiments, we can try to 
find something in a more DIY-friendly package.

Speaking of DC/DC converters, they can be divided into three general 
types. The first type includes bare controllers. They are very small and 
cheap, because they contain only control circuitry, they require several 
external components (power switch, inductor, diode, capacitors). They 
are typically used when large output current is required. Since we need 
only about 50 mA, we don't need this type of converter.

Converters of the second type have control circuitry and internal power 
switches. They still require external inductor, diode and capacitors, 
you also have to do some math to calculate required inductance value. 
These converters require prototyping, because you must check that you've 
selected appropriate inductor.

The third type of converter is a regulator module. Such converters have 
built-in inductors and diodes, so they only require input and output 
capacitors. LTM8045 is an example. I've suggested to use it, because it 
is straightforward to use, you don't need to prototype it. It has PCB 
layout example in the datasheet that will 100% work from the first 
attempt. When I recommended this module, I thought, that paying a few 
extra bucks would be better than dealing with inductors and diodes.

Anyway, as far as I understand, Joachim is back, so you're going to have 
a meeting with BitSim guys soon. You can ask them about this issue. Tell 
them, that besides digital components, you have sensitive analog 
circuit, that requires stable +12V (probably higher) and draws about 50 
mA. Let's listen to what they say.

--
With best regards,
Pavel Shatov