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I have a power regulator with an output enable that can be used to shut the regulator off without actually unhooking it. I am trying to figure out how to control that using a GPIO port of a Jetson TX2 (1.8V logic).

The manufacturer of the regulator says that I will not be able to connect the output enable wire directly to a 1.8V GPIO pin because the output enable is internally pulled up to the regulator Vin (24V). They said to drive it properly I will need an open-drain circuit, which will allow your GPIO to switch the output enable pin between float and ground.

Using https://www.microcontrollertips.com/what-is-an-open-drain/ as a source I looked on Digikey to find an N-channel MOSFET that would work and I think one of these:

https://www.digikey.com/product-detail/en/toshiba-semiconductor-and-storage/SSM3K329RLF/SSM3K329RLFCT-ND/3522426

https://www.digikey.com/product-detail/en/nexperia-usa-inc/PMV40UN2R/1727-1900-1-ND/5056345

would. Is creating the open drain circuit a matter of connecting the output enable wire of the regulator to the mosfet drain, the Jetson GPIO to the gate and the mosfet source to ground like this? Or do I need a current limiting resistor between the GPIO and the gate?

schematic

simulate this circuit – Schematic created using CircuitLab

Thanks for your help.

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  • \$\begingroup\$ Yes, use a resistor.. electronics.stackexchange.com/a/343286/139766 \$\endgroup\$ – Trevor_G Jan 9 '18 at 17:36
  • \$\begingroup\$ @Trevor I think the OP means a resistor on the drain, not the gate (but I may be misinterpreting the question). My questions: what's the regulator part number? How fast do you intend to switch? \$\endgroup\$ – awjlogan Jan 9 '18 at 18:42
  • \$\begingroup\$ No I do mean for the resistor on the gate. The regulator is a custom assembly from an oem for a gimbal I'm using. I am assuming the max current allowed from the GPIO is 1 mA, so that would mean an 1.8k ohm resistor. I'm not sure how that affects the timing for turning on the MOSFET. The intended use is to turn the GPIO on once every 10 or 15 mins for 3-5 seconds (to do a power reset on the gimbal. \$\endgroup\$ – schrödinbug Jan 9 '18 at 19:21
  • \$\begingroup\$ Maybe I'm barking up the wrong tree with trying to use a MOSFET. I found this: elinux.org/Jetson/Tutorials/GPIO which I think I could adapt by only connecting the regulator output enable wire to the collector of the transisitor. \$\endgroup\$ – schrödinbug Jan 9 '18 at 19:32
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Either the MOSFET or the BJT will work.

You might find the transistor (leaded type) easier to work with and it has a bit more margin on the voltage (45V vs. 30V on a 24V circuit).

Personally I would add a resistor with the MOSFET gate (something like 10K) to make it a little less likely to damage that $500 computer board. It will slightly slow it down (microseconds). It's not necessary for the MOSFET. It is necessary for the BC547 BJT.

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