Step-down regulator problem
November 12, 2012
I've been using an LM2940CT-based regulator to power the logic on a Dagu 4ch motor controller. It's one of OddBot's designs from his walkthrough and it works just fine.
I decided to buy a Pololu D15V35F5S3 to replace it simply because it's much smaller than the one I built.
Before using it, I decided to have a look at the output on my scope and got a reading of 0V. I checked the input terminals and found a good 8V so I unplugged the battery and tried again. This time it was close enough to 5V. After much testing, and occasionally getting 0V output, I noticed that it's quite sensitive to the way you connect the battery and shuts down if I don't plug the bullet connectors together cleanly.
After digging through their website, I found that this seems to be documented where it talks about ensuring that the rise time on the input should be less than a few milliseconds or it will latch into an error state.
I asked about this on the Pololu support forum a few days ago but didn't get an answer so I'm going to stick with the LM2940 to make sure I don't get any magic smoke from applying the motor supply without power to the logic.
Is anybody successfully using this reg or has found the same behaviour and solved it? I'm sure it's a nice reg but just seems too risky for this particular application.