Poor PWM output when running Jetson AGX Xavier through external level shifter

I’m trying to use the Sparkfun BOB-12009 level shifter (https://www.sparkfun.com/products/12009) to convert PWM signals from 3.3V (coming from a Jetson Xavier AGX) to 5V (driving an Actuonix 12V linear servo, which uses a 0-5V PWM signal as an input - example: https://www.actuonix.com/L12-I-Micro-Li … /l12-i.htm). I am getting garbage results. Here’s what happens:

  • When the Jetson’s pins are not hooked up to the BOB-12009, everything looks fine - the 3.3V reference reads as 3.3V, the PWM signal is as expected.
  • When I plug the Jetson into the BOB-12009, the PWM signal still looks good, but the low value has been raised - now it’s at 1.8V instead of 0V. At this point, I have 3.3V from the Jetson to LV, GND to GND, and PWM (Pin 18) to LV1. Nothing is hooked up to the HV side.
  • When I plug in the leads to the HV and GND ports on the other side of the BOB-12009 - even before I’ve turned the power supply on - the PWM waveform shifts again, now going between 750 mV and 2.6 V. Note that the GND ports on the HV and LV sides are connected, so all my grounds should be at the same level here.
  • When I power up the 5V power supply, the signal shifts again, and the bottom half of the PWM waveform now gets really fuzzy. The high signal is back up to 3.3V, but the low signal is a fuzzy mess around 1.5V. (IIRC there is a display setting on my o-scope that may be impacting this/why it looks so “fuzzy”, but I can’t remember what it is/need to go look for it)
  • At this point, if I prove HV1 with my scope, it looks “appropriately bad” - high signal is at 5V, low signal is a gross mess also around 1.5V.
  • Finally, if I connect HV GND to my servo ground; turn on the 12V power feeding my servo; and connect the servo PWM pin to HV1, both the HV and LV signals get even smaller: LV is 1.6 to 3.3 V, and HV is 1.6 to 2.6.

What am I doing wrong here? My suspicion is that I need to place a pull-up or pull-down resistor on the PWM output of the Jetson - but I haven’t been finding any clear guidance either way (and my EE is too poor to feel comfortable guessing on this one - don’t want to smoke my Jetson!)

Thanks, all!

Basically we don’t have suggestion to this kind of 3rd-party devices, hope someone has similar experience can be shared.

For Jetson itself, the GPIO35_PWM pin is from level shift TXB0108RGYR as you can see in the P2822 schematic. For this level shift, there is below relevant doc for your reference, there are some requests on its load.

https://developer.nvidia.com/jetson-nano-developer-kit-40-pin-expansion-header-gpio-usage-considerations-applications-note

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.