IO protection / isolation on ZED-F9P boards

GPS/GNSS Development Boards
1

My question is specific around the isolation / buffering of the ZED-F9P module, as strongly suggested by the uBlox integration manual of said device.

I have gathered that they strongly suggest isolation components like SN74CB3Q16244DL (from the manual), or the 74LVC4066D_QUAD_BILATERAL_SWITCH and the 74LVC541A as used on the

“SparkFun MicroMod GNSS Function Board - ZED-F9P” (GPS-19663)

But I have noticed that isolation was not used (it seems) on any of the following, while still using the ZED-F9P:

SparkFun GPS-RTK2 Board - ZED-F9P (Qwiic) (GPS-15136)

SparkFun MicroMod GNSS Carrier Board (ZED-F9P) (GPS-17722)

SparkFun GPS-RTK-SMA Breakout - ZED-F9P (GPS-16481)

Why did only the GPS-19663 get some isolation?

Is it because it can be hot-swopped on the “SparkFun MicroMod Main Board – Single” (DEV-18575) and maybe have V_BCKP connected while VCC is off?

And did the others not get isolation since they will be off once USB is disconnected? Or that it is highly unlikely that board mods will be done while unit is off, but power (and backup) is still connected.

2

Moved topic to GPS forum

3

Hi @Joueur,

It’s a good question. The short answer is: it depends on the application.

The “protection” circuits are there to: prevent power being applied to the IO pins when the main VCC is disabled; and to prevent possible damage if the wrong IO voltage is used.

The MicroMod Function Board is a special case because it could indeed be hot-swapped.

For our other boards, the power is provided by the connected microcontroller board - or the connected interface - and so there is little risk of the IO pins being driven while VCC is off. We do add 33 Ohm resistors just in case.

Best wishes,

Paul

4

Hi Paul

Thank you very much for the clarification.

I intend doing just that, buffering the IOs since we will also use the modules powered with backup supply, and having to swop them out for maintenance.

Kind regards