Raspberry Pi GPIO Enable for S18V20F5 Supply

[amcdonley]

My Raspberry Pi 5 robot has an S18V20F5 Pololu supply driving the LIDAR and Oak-D-Lite stereo depth camera.

I need to be able to disable the supply when the Raspberry Pi 5 is napping (usually on its dock), or when the Pi5 decides the camera and LIDAR are not needed to extend the “playtime”.

For Raspberry Pi GPIO (3.3v) to enable S18V20F5:

Disable when RPi is off, enable with GPIO pin high 3.3volts.

The spec says the S18V20F5 has a 100k ohm to VIN which in my case is 9.6-12.6v.
Why does my VOM measure 33k ohm when I measure from VIN+ terminal to Enable through-hole?

Doesn’t the “open input” voltage divider have to get the Enable below 0.7v (reliably)?

So GPIO pin to the Enable line, with 2-4k pull-down (to gnd) for 100k ohm pull-up?
If the pull-up is indeed 33k ohm, I need a 1k pull-down to gnd to get .0.35v to the enable when the RPi is “off”?

Does the GPIO pin need reverse polarity protection?

*** GoPi5Go Dave TOTAL LIFE STATISTICS ***
Total Awake:   280.85  hrs
Total Naps:     56.05  hrs
Total Life:    336.90  hrs (since Mar 17, 2024)
Sessions (boot):  45
Average Session:  6.2 hrs
Safety Shutdowns:  3

[Claire]

Hi.

That looks like a fun project. You are correct; the EN pin on the S18V20F5 must go under 0.7V to disable the regulator. The pull-up should be 100k. It can be hard to accurately measure resistances while they are inside a circuit. Make sure you are measuring it with nothing attached to EN and with the power off.

Regardless though, it sounds like you want the regulator to be default off and only come on with 3.3V from an I/O pin. For that, I recommend removing the pull-up and adding an external pull-down. Here is a picture showing the pull-up’s location:

There is no protection built into the board to protect an I/O pin connected to EN, so if you want some, you would have to add it.

-Claire