Path: ...!2.eu.feeder.erje.net!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: +48 precharge Date: Sun, 24 Mar 2024 20:58:22 -0000 (UTC) Organization: A noiseless patient Spider Lines: 47 Message-ID: References: <02210jhti2lc71037fh4q9sbs1ved2oc63@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sun, 24 Mar 2024 21:58:22 +0100 Injection-Info: dont-email.me; posting-host="d16e937bfd4c49da0da38ff5f79e7417"; logging-data="630156"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18WZPDoq61plf9l0w00c4QM" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:MEaYPvX9GpVdwAc6n8Ahg+man1k= sha1:PHJg6PyVYs7PI4RUpST/SJKgj5s= Bytes: 2710 Joe Gwinn wrote: > On Sun, 24 Mar 2024 12:14:57 -0700, John Larkin > wrote: > >> >> We have a board that tends to blow up. >> >> It has a couple of isolated dc/dc converters, gate driver chips and >> big mosfet full-bridges driving transformers. The gate drivers get >> their inputs from an FPGA. >> >> The probelm is that the +48 volts to the h-bridges comes up at power >> turn-on, but the FPGA is configured some minutes later, after Linux >> boots up. And I don't entirely trust the FPGA outputs meanwhile. >> Possibly never. >> >> After designing many complex fixes, a simple fix is to precharge the >> module's +48 rail gently, and slam it on hard after everything is >> verified stable. >> >> >> >> >> >> The one-shot gets its I'M OK trigger from the FPGA, which can only >> happen if the FPGA is working, I hope. > > Can you require significant net charge transfer on a short period of > time from the FPGA before the one-shot will trigger? > > Joe Gwinn > There are any number of ways to reject FPGA zombie behavior. The retriggerable one-shot is pretty simple. Another fairly simple one would be making the processor wait to receive a specific message from the FPGA, e.g. “Tranquility Base here. The Eagle has landed.” Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics