[EE]: Low Voltage, High current H bridge reccomendations

[Denny Esterline]

I'm considering a project that would repurpose a small cordless power
screwdriver. It has a single 18650 lithium cell and the motor draws about
20A at stall. The existing control switch is a crude mechanical design
that's not suitable for my application, so I'm looking to replace it with
an H-bridge.

I'm only looking for on/off control, several seconds of on time minimum -
not at all a high frequency design.

My current thinking is an H-bridge of four discrete N-FETs and driving them
with four photovoltaic opto-isolators. I shouldn't need the isolators for
the low side, but they also boost the drive voltage higher than the 3.3V I
can get out of the logic. At these voltages I can get FETs with well less
than 10 mOhm Rds on values.

I'd definitely be interested in a integrated H-Bridge part, but I've not
found one with suitable voltage and current ratings.

Thoughts? Suggestions?


-Denny

.

[RussellMc]

Discrete FETs sounds reasonable.

This Digikey search may (ormay not) help

https://www.digikey.com/products/en/integrated-circuits-ics/pmic-motor-drivers-controllers/744?FV=2040480%2C20406fa%2C2040889%2C2040122%2C2040056%2Cffe002e8%2C1f140000%2C1f140007&mnonly=0&ColumnSort=1000011&page=1&stock=0&pbfree=0&rohs=0&cad=0&datasheet=0&nstock=0&photo=0&nonrohs=0&newproducts=0&k=bridge&quantity=&ptm=0&fid=0&pageSize=500&pkeyword=bridge

Not much more than 3 half bridges in a case.
9.5 mOhm max.
Excessively high gate voltages
$8.33/1
http://www.onsemi.com/pub/Collateral/STK984-190-E-D.PDF

Much more integrated.
50 mOhm :-(
3V logic drive
$4.33/1
http://www.st.com/content/ccc/resource/technical/document/datasheet/6b/3d/8c/73/0c/a2/44/5e/CD00241540.pdf/files/CD00241540.pdf/jcr:content/translations/en.CD00241540.pdf


R