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diff --git a/doc/altusmetrum.xsl b/doc/altusmetrum.xsl index 0785f65a..cd78d5f2 100644 --- a/doc/altusmetrum.xsl +++ b/doc/altusmetrum.xsl @@ -5831,6 +5831,58 @@ NAR #88757, TRA #12200 </section> </appendix> <appendix> + <title>Igniter Current</title> + <para> + The question "how much igniter current can Altus Metrum products + handle?" comes up fairly frequently. The short answer is "more than + you're likely to need", the remainder of this appendix provides a + longer answer. + </para> + <section> + <title>Current Products</title> + <para> + The FET switches we're using on all of our current products that + have pyro channels are the Vishay Siliconix Si7232DN. These parts + have exceptionally low Rds(on) values, better than 0.02 ohms! That + means they aren't making a lot of heat... and the limit on current + is "package limited", meaning it's all about how much you can heat + the die before something breaks. + </para> + <para> + Cutting to the chase, the Si7232DN specs are 25 amps *continuous* at + 20V at a temperature of 25C. In pulsed mode, they're rated for 40A. + However, those specs are a little mis-leading because it really is + all about the heat generated... you can get something like 85A + through one briefly. Note that a typical commercial e-match only + needed about 13 microseconds to fire in tests on my bench a couple + years ago! + </para> + <para> + So a great plan is to use something like an e-match as the initiator + and build up pyrogen(s) as required to actually light what you're + trying to light... But if you want to use a high-current igniter, + we can probably handle it! + </para> + </section> + <section> + <title>Version 1 Products</title> + <para> + The FET switches used on TeleMetrum v1 and TeleMini v1 products + were Fairchild FDS9926A. The Rds(on) values under our operating + conditions are on the order of 0.04 ohms. These parts were rated + for a continuous current-carrying capacity of 6.5A, and a pulsed + current capacity of 20A. + </para> + <para> + As with the more modern parts, the real limit is based on the heat + generated in the part during the firing interval. So, while the + specs on these parts aren't as good as the ones we use on current + products, they were still great, and we never had a complaint about + current carrying capacity with any of our v1 boards. + </para> + </section> + </appendix> + <appendix> <title>Release Notes</title> <simplesect> <title>Version 1.4.1</title> |