Digging around the web and here at EEVBlog, I see plenty of different ways to attack reverse polarity protection combined with overvoltage protection. I've seen some complicated multi-discrete part circuits as well as recommendations to just buy an off-the-shelf chip. After a dozen hours of searching via Google and wandering Mouser/Digikey, I'm beginning to think "I don't know what I don't know".
Desirable traits:
- work well for 3.3V or 5V rails (does not have to be same part number)
- low on resistance or voltage drop (this precludes diodes)
- minimize # components and no BGA designs (other SMD ok)
- lower cost is always better, $5 for the components at qty 10 is a target
- actually be stocked at Mouser or Digikey
I don't need:
- Battery management
- Current monitoring (can be handled with a PTC fuse on input)
The P MOSFET for reverse polarity becomes an issue with <=3.3V rails since the the gate drive voltage could leave a high R
ON value in the linear region. Overvoltage protection seems to turn into a pile of discrete transistors and diodes.
I found this Maxim 4866L (
Mouser link,
Datasheet). It requires a complementary MOSFET or 1P/2N channel MOSFETs to function (page 1 and page 8 of datasheet). It has a built in charge pump to solve the low gate voltage problem. The undervoltage lockout is a bonus. Unfortunately the series is offered only with overvoltage trip levels of 7.4, 6.35, 5.8, and 4.65. The 5.8 V is perfect for 5V USB but the series does not go low enough.
The Maxim chip is the only such beast I've been able to find. I can't figure out what my search terms should be or if maybe I'm chasing a non-existent part. I can't seem to get to a usable parametric search and have to browse hundreds of parts manually and nothing close the Maxim chip showed up so far. I want a simple low cost solution that I can re-use in multiple board designs. Am I approaching this problem correctly?
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