My 18v25 Driver's DIR pin seems to be shorted to ground


Today I received an 18v25 High-Power Motor Driver (your product 758?) and started hooking it up to my project.

I was surprised to find that I couldn’t drive the DIR pin high from the 3.3 V to 5 V level shifter I’m using (my MCU in this project has 3.3 V I/O).

After powering everything down and probing, DIR seems shorted to ground… (< 1 ohm with a DMM, probing in both polarities, so it’s not diode-like).

Aside from DIR, other behavior seems OK. I can run the motor by wiggling the PWM pin from the same MCU through the same level shifting circuit. I just can only run it one direction :wink:

The level shifter is powered by the 5V out on the 18v25 board. Your docs indicate this can only supply a couple mA, but that rail appears to be staying at +5 V as I wiggle the inputs, so I don’t think it’s overtaxed. The 18v25 is powered by a bench power supply; I’ve been playing with both 6 V and 12 V.

I noticed a possible solder bridge on a couple pins on the unmarked SOIC-28(?) that I presume is your MCU. But it’s on pins that are also tied together on the PCB, so should be OK. The board looks OK and there is no sweet smell of silicon death :slight_smile:

I would expect DIR to be a CMOS/TTL kinda high-impedance input and shouldn’t look like GND to my DMM. PWM, by contrast, does look like I’d expect (and that pin seems to work).



What you’re doing generally sounds reasonable, and the DIR pin should not be forced low by the board. We do test each board before it ships, and I cannot tell from your description what might have caused the problem. If you email us with your order number, we can send you a replacement.

- Jan

Thanks Jan, I will email to follow up.

The replacement arrived this morning and is working perfectly. Thanks to Jan and Linnea and Pololu in general for great support.