#avr Logs

Oct 29 2021

08:25 AM exp: boy it's impossible to get even small quantities of some high side switches now
08:33 AM exp: going to have to order the last of digikey's stock, for the third or fourth time
10:39 AM user____: .
10:39 AM user____: Real men diy high side switches, unless automotive performance and self checking is needed
10:39 AM exp: it's not a trivial thing to do
10:39 AM user____: Just a PMOS and a little care for gate drive considering high and low supply.
10:40 AM exp: that's not really a high side switch though is it
10:40 AM user____: It is trivial unless you need automotive temperature range, inrush limit, self test etc.
10:40 AM user____: exp: it is a high side switch.
10:40 AM exp: user____: no 'high side switch' has specific connotations
10:40 AM exp: that's why it's its own category
10:40 AM exp: an alternate take: real men make their own LDOs
10:41 AM exp: it's just a BJT after all
10:41 AM user____: I beg to differ
10:41 AM exp: there's a bit more to it than just that ;-)
10:41 AM user____: https://electronics.stackexchange.com/questions/300605/high-side-p-mosfet-circuit
10:41 AM exp: yes I do understand what a PMOS is
10:41 AM user____: the lower BJT can be a jumble 2N7002
10:41 AM exp: i use a similar topology for PWMing 12v LEDs
10:42 AM user____: Well if you do understand then you know what is needed.
10:42 AM exp: but the amount of circuitry you'd require just to do the basics is far too much
10:42 AM user____: lol
10:42 AM exp: inrush limiting, open load detection, short circuit detection, output discharging etc etc
10:42 AM exp: plus the units i like have adjustable current limiting and some sort of current sensing
10:42 AM user____: Ah. Then you do need all that and need to plan ahead.
10:42 AM user____: Ordering parts in these viral times.
10:43 AM exp: indeed, unfortunately i have a boss who looooves to sell
10:43 AM exp: and turns out he's sold a bunch of 30v stuff and I don't have good stock of TPS27S100s or similar
10:43 AM user____: Then, you need to talk with your boss about selling his 1st born for stock now.
10:44 AM exp: oh I think he would try
10:44 AM user____: Automotive being unobtainium now.
10:44 AM exp: I've been waiting weeks hoping that Ti would bring some of their preview parts to general availability
10:44 AM user____: His granny he already sold, right? <wink>
10:44 AM exp: because i've scored a few little caches of those
10:44 AM exp: unfortunately nothing has become available that i've seen, and their USB-C extended power range stuff is still closed access
10:45 AM user____: Oh you need USB power control? Wow.
10:45 AM exp: need to pick up at least 500 bidirectional controllers ASAP there, it's quite frustrating
10:45 AM exp: for the moment this is a battery powered product with a standardish 24v in
10:45 AM user____: 24V automotive or not?
10:45 AM exp: but given usb-c is now extending into the ~200W range, it's foolish to not offer that as an option
10:45 AM exp: not exactly, it's not fitted into vehicles but it is fitted to them
10:46 AM user____: Looked at the usual suspects? Infineon etc?
10:46 AM exp: i try and use automotive where possible for things, load-dump protection and the like
10:46 AM exp: i don't know infineon's usb-c stuff at all, haven't had time to dig in there yet
10:46 AM user____: VN**
10:46 AM exp: oh i have a few 5050s and the like
10:46 AM exp: stock is poor for those
10:46 AM user____: Indeed.
10:47 AM exp: managed to get my hands on ~2000 NMOS which are ideally suited to our current supplies
10:47 AM user____: Are you using AVRs to control the project?
10:47 AM exp: so currently my fight is on simulating the switching waveforms, fun
10:47 AM exp: yeah xmega C3s
10:47 AM exp: they were available and have the hardware needed, probably not ideal but that's how things are right now
11:02 AM user____: https://www.maximintegrated.com/en/site-search.html#q=high%20side%20switch&sort=relevancy
11:03 AM user____: [assuming you can find any stock]
11:04 AM user____: https://duckduckgo.com/?q=infineon+high+side+switch&t=ffsb&iar=images&iax=images&ia=images
11:07 AM user____: https://www.maximintegrated.com/en/products/power/mosfet-drivers-controllers/MAX14922.html etc
11:07 AM user____: have fun.
11:08 AM user____: And I keep saying "automotive" for a reason. As you know, 24V automotive is a very different kind of hairball from 24V "other" usages.
11:16 AM exp: indeed it is
11:17 AM exp: in this case I have a TPS2493 doing the input 'protection'
11:17 AM exp: and the battery charger is a BQ25720, if you're interested
11:17 AM user____: Sounds like one of those money is no object designs so far...
11:17 AM user____: I hope you have customers
11:17 AM exp: the high side stuff I need is mostly internal, but things like hiccups are important to protect parts
11:18 AM exp: we produce these in quantities of dozens rather than hundreds or thousands
11:18 AM exp: and per unit cost is dominated by nonsense stuff like connectors
11:18 AM specing_ is now known as specing
11:18 AM user____: As I said, as long as you have customers, why not.
11:19 AM exp: indeed, we haven't gone through torture testing on these yet but i'm now designing the 'final' revision
11:19 AM exp: so we'll be doing the usual load-dump, reverse polarity, alternator disconnection type tests
11:19 AM exp: reverse polarity protection is a tricky thing in this scenario, mostly due to part availability
11:20 AM exp: a nice fat PFET would burn way too much power to fit in the case
11:20 AM user____: Right, so, automotive. Good luck.
11:20 AM exp: haha thanks, I also want to smash EMC testing because there's some potential RF stuff to be plugged in
11:20 AM exp: so aiming for mV levels of ripple and noise
11:21 AM exp: it's been a real challenge
11:21 AM user____: I hope your boss is not lunatic enough to let you design a non automotive circuit then later ask for it to be "upgraded" to automotive.
11:21 AM user____: (and I hope you are not letting him dupe you into doing it)
11:21 AM exp: not to worry, i took over from a consulting company who's total input protection was a BNX025 and literally nothing else
11:22 AM user____: Again, DID someone pressure designers to cut corners then wanted automotive? That's a yes/no question. Sounds like "yes" so far.
11:22 AM exp: probably
11:23 AM exp: I wasn't with the company then, but now I define our protection requirements
11:23 AM user____: Right, so you dropped into someone else's shoes and will face the grilling for whatever they grandfathered upon you.
11:24 AM exp: luckily it's not too bad, there was no active control, battery chargers were all external rebranded chinese generics etc
11:24 AM user____: Ouch.
11:24 AM user____: https://oldcomputers.net/cc-40.html cute thing
11:24 AM exp: it's more or less a niche industrial startup
11:24 AM exp: so they've had a lot to learn, and so have I
12:15 PM user____: Stacked DIP RAM chips! And it's by IBM! Yay. https://oldcomputers.net/pics/ibm5322-memory.jpg from https://oldcomputers.net/ibm5322.html
12:15 PM user____: I never thought the big guys used these hacks.
12:16 PM user____: 1979.
12:17 PM * user____ wonders how they sorted the CS pin? Would like to see the board from the other side.
12:17 PM user____: Being IBM maybe they special made/ordered RAM chips with CS and ~CS for top and bottom.
12:18 PM user____: So they simply shadowed each other, identical, for reliability. Sigh.
12:38 PM Ekho- is now known as Ekho
12:41 PM user____: https://oldcomputers.net/gridpad.html very early tablet
01:35 PM user____: https://www.theregister.com/2021/10/29/2021_dcma_rules/
04:15 PM exp: nice to see updated dmca rules
04:15 PM exp: still illegal to jailbreak your own tablet i suspect
04:44 PM rue_mohr: I dont talk a lot in here, but when is the last time anyone heard anything from E***?
04:53 PM Phantom: a while ago
11:19 PM specing_ is now known as specing