Update 2, the VOL3120 circuit now works as expected. I just need to load test it and test shutoff via the in situ circuit. I'd still like to know what I did wrong with the UCC version of the circuit so if in your expert eyes you see something in the schematic that jumps out as obviously incorrect please let me know. Otherwise this is now an academic exercise rather than critical path in my job :-) Thank you! DougM On Fri, Jun 28, 2019 at 11:16 AM doug metzler wrote: > Update, the problem with the VOL3120T was reversed pins in the library. > It now works, so although the latch circuit doesn't work I have at least > unraveled one mystery. > > Manu, I designed the circuit from the ground up, so the schematic is > original. > > Here is the datasheet for the FET. > > > https://www.infineon.com/dgdl/irlr3636pbf.pdf?fileId=3D5546d462533600a401= 53566d1e122698 > > It has been my understanding that FETs at high voltages (like 24) don't > fully open with 3v3 at the gate, hence the driver (plus it helps to have = 2 > logic inputs available) but perhaps I'm not using the correct FET. > > Also, this circuit cannot have any standby current, so I can't have 3v3 o= r > other voltages available at/before turn on time. > > I will check the footprint for the UCC and make sure it wasn't another > dumb mistake. > > Thank you, > > DougM > > > > On Fri, Jun 28, 2019 at 10:08 AM Manu Abraham > wrote: > >> Hi, >> >> Could not find a datasheet for the FET .. >> >> That said .. >> >> I wonder how you arrived with the attached schematic ? >> >> Have a look at the datasheet: >> http://www.ti.com/lit/ds/symlink/ucc27537.pdf >> >> Cheers, >> Manu >> >> >> On Fri, Jun 28, 2019 at 9:54 PM doug metzler >> wrote: >> > >> > I'm trying to design a circuit that takes a 24VDC input signal to powe= r >> a >> > downstream system (motor driver board). It's about 16A peak. The >> trick is >> > it needs to latch, and it needs to be turned off with a logic level >> signal. >> > >> > I thought I could just use a FET and a driver chip, but I've tried 2 >> > different drivers and as soon as I power the circuit the driver chips >> > smoke. I tried the VOL3120Tand the UCC27537DBVR. The VOL smokes >> > immediately. The UCC works the first time, but you can watch the >> > components get destroyed as somehow high power gets to the signal side >> the >> > second time. >> > >> > Clearly there is something I don't understand. I'm attaching the UCC >> > schematic, which I thought was a simple solution. >> > >> > [image: image.png] >> > >> > Thank you for any help, I'm completely flummoxed by this one. >> > >> > DougM >> > -- >> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> > View/change your membership options at >> > http://mailman.mit.edu/mailman/listinfo/piclist >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .