search

interoberlin / nRF51-Boards

Some PCBs with a Nordic Semiconductor nRF51822, designed with Altium
Other
8 stars 1 forks source link

DevBoard: Replace FETs by BJTs #9

Closed matthiasbock closed 8 years ago

matthiasbock commented 8 years ago

The Voltage Level Shifting relies on N-channel FETs on the high side... This setup is suboptimal, if it will work at all. npn-Transistors should be used instead.

...replace all 2N7000s by KST5551s.


matthiasbock commented 8 years ago

"...which may operate on any voltage between 3.3V and 5V."

matthiasbock commented 8 years ago

James Reuben writes on his blog, that pull-resistors should be chosen with a low value.

Signal translation at 117kHz with 10k resistors:

With 200R resistors:

Input signal in Yellow, output in Blue.

I think, 200R would result in unacceptable power losses when the transistors are switched conducting.
Also, a low D-R2 could disturb signal propagation through the SWD Resistor Hack, by pulling SWDIO output from the microcontroller to low.
In case, 5k6 are too high, 2k could be an acceptable compromise.

matthiasbock commented 8 years ago

Neither with FETs nor with BJTs a translation to a higher voltage level is possible.

matthiasbock commented 8 years ago

obsolete: no voltage translation implemented