HP97 The journey begins

[Harald]

(05-07-2019 01:49 AM)teenix Wrote:  

(05-05-2019 09:36 AM)Harald Wrote:  Thanks for the schematic and layout. You have kept the Cathode of D3 close to C8, that is good. But the track from U7 pin 1, which is the internal switch, to D3 is quite long. You would want to keep that as short as possible to minimize inductance in that path. You are better of moving the choke a bit further away and moveing the diode closer.
It is important to place diode and input and output capacitor close to the IC. You need to minimize path length in all the paths that carry switched currents. The inductor path is not critical.

Hi Harald,

I have squeezed all the relevant parts as close as I can to the IC and given it as much ground plane as I can. Hopefully better.

However, it might be a moot point now. I can't fathom why I was not doing an inductorless design. I had it in my mind that I was looking at reasonably high currents but that is not the case. The new CPU board only draws a few milliamps as does the reader chip, so I think I will scrap the inductor. I've ordered some oscon caps and an LM2665M6 which is similar to Maxim but way cheaper just to try out.

cheers

Tony

cheers

Tony

Hi Tony,

Yes, that does look a lot better now! Still, if you can do the charge pump, that would be the better solution in my opinion.

Cheers,
Harald