Any insight for Automotive Sensor Inputs/ Front-End Protection.
in [Design]
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From: John Devereux on 29 Apr 2010 10:52 Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> writes: > On Thu, 29 Apr 2010 07:30:11 +0100, John Devereux > <john(a)devereux.me.uk> wrote: > >>Joerg <invalid(a)invalid.invalid> writes: >> > [snip] >>> >>> Figure 1, for a dose of reality: >>> http://www.automotivedesignline.com/howto/205101011 >> >>Hi Jeorg, >> >>That LTC part will likely blow up before the simple resistor+opto >>solution. The Ford load dump pulse is only 60V peak with 150ms decay >>time constant. > [snip] > > Alternators have been improved over the years. In my day (mid '60's) > you could see _400V_! There are some other test pulses defined with much higher peaks but these are much shorter - ~microseconds rather than ~100ms. And of course ESD is kV for ns. It might be well be wise to have TVS or capacitors in there for for these. And once you have all that what is the opto for? > So, above 20V, my field driver devices turned off and went into BVCER > mode and rode out load dump. > > The control chip itself was low current, so a series carbon resistor > plus an active "zener" on-chip sufficed for protection. > > (Everything bipolar.) > > ...Jim Thompson -- John Devereux
From: Joerg on 29 Apr 2010 11:25 Jim Thompson wrote: > On Wed, 28 Apr 2010 18:45:51 -0700, Joerg <invalid(a)invalid.invalid> > wrote: > >> Jim Thompson wrote: > [snip] >>> YOUR problem, as a designer, is that you must use off-the-shelf stuff >>> that is not designed to withstand abuse, and ADD stuff to it to make >>> it survive. >>> >> Yes. So why then did you say that TVSes make simple problems difficult? >> That's plain wrong, and unsurprisingly you haven't been able to come up >> with the simpler solution to the (quite common) problem I presented. >> Because there is no simpler or lower cost solution than a TVS. >> >> >>> MY problem, when designing a chip, is to make the circuit survive on >>> its own, in the first place. Over the years I've become most clever >>> at that skill :-) >>> >>> MY '60's designs survive load dump. Wonder how ?:-) >>> >> That wasn't the issue in this thread. We (and that includes the OP) have >> to live with what's available at Arrow, Digikey and so on. Clients do >> not have half a million bucks and one year of patience to wait for a >> better chip that then saves 15c in discretes, and maybe amortizes over a >> decade, or never. They want the solution here, now, and cheap. And they >> get that solution. That's life. > > I was just arguing that there's usually a clever approach that doesn't > even need the expense of a TVS. > > "Life" is good design, not patches. > Board level designers do not have a chance to change the innards of a chip. The use of TVS on their part is typically a very smart move. In most cases there is no lower cost alternative, none. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Joerg on 29 Apr 2010 11:36 John Devereux wrote: > Joerg <invalid(a)invalid.invalid> writes: > >> Jim Thompson wrote: >>> On Wed, 28 Apr 2010 18:09:18 +0100, John Devereux >>> <john(a)devereux.me.uk> wrote: >>> >>>> Johnny5 <dirtylogicdesigns(a)gmail.com> writes: >>>> >>>>> On Apr 26, 6:35 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >>>>> Web-Site.com> wrote: >>>>>> On Mon, 26 Apr 2010 16:18:05 -0700, Joerg <inva...(a)invalid.invalid> >>>>>> wrote: >>>>>> >>>>>>> Jamie wrote: >>>>>>>> Johnny5 wrote: >>>>>>>>> I was curious if anyone had any insight into protecting an Opto- >>>>>>>>> isolator LED input from load dump, Jumpstarts, and many of the other >>>>>>>>> signals in the auto environment. FETS,CLIPPERS,Clamps? >>>>>>>>> Thank you in advance, >>>>>>>>> It is an open drain SSR. >>>>>>>> TVS diodes. Transorbs is another name for them. >>>>>>> Also Transzorb. And ST calls them Transil. It's trade names, like >>>>>>> Kleenex or Kim Wipes. >>>>>>> [...] >>>>>> No canned answers. It depends on the circuitry. >>>>>> >>>> [...] >>>> >>>>> Thank you all for the input, a little more on the circuit . Sensors >>>>> are pressure switches/Temp that are connected to Vbatt. Pressure High= >>>>> relay that switches Vbatt on/off. No current Limit. So I was thinking >>>>> it would be best use opto. HSR312 SSR, Vr=7v, Vf=1.6V , control >>>>> current approx 2mA. >>>>> >>>>> >>>>> Automotive opto front end for Vbatt switched with no current limit >>>>> >>>>> Bav99/ TVS with a current limiter suffice? ? >>>>> polarity protection p channel fet as well? any choice on fet, dmos >>>>> only? >>>>> thks >>>> Do you actually need to do anything? LEDS will survive brief overcurrent >>>> just fine. If you size the LED resistor for 12V operation near the 2mA, >>>> you will have to get up to 100V or so to even get to its rated 25mA >>>> maximum. Any such pulses will be very brief, the LED won't mind. >>>> >>>> I would just use a series resistor and connect a signal diode in >>>> anti-parallel across the LED. >>> There you go! >>> >>> So many posters here want to make simple problems difficult... TVS's, >>> etc :-] >>> >> Those posters tend to design reliable electronics :-) >> >> Figure 1, for a dose of reality: >> http://www.automotivedesignline.com/howto/205101011 > > Hi Jeorg, > > That LTC part will likely blow up before the simple resistor+opto > solution. The Ford load dump pulse is only 60V peak with 150ms decay > time constant. The resistor+opto will survive 100V > indefinitely. Furthermore is is extremely likely to survive pulses of > much higher voltage, while the LTC part is extremely likely to fail. > I only brought that link to show the shape of a load dump spike because some readers may not know. In aerospace those spikes are a whole lot tougher because the voltage can stay up there for a second, and it can happen several events in a row. This gets tested so a product that fails wouldn't even make it to field testing. And shouldn't. > Yes, of course you can make it still more robust with a R+TVS+R feeding > the LED. > Exactly. That's typically the lowest cost solution because TVS are ubiquitous and very cheap. Not using them is, in many cases, like driving around without wearing a seat belt. [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: miso on 29 Apr 2010 13:09 On Apr 26, 3:35 pm, Johnny5 <dirtylogicdesi...(a)gmail.com> wrote: > I was curious if anyone had any insight into protecting an Opto- > isolator LED input from load dump, Jumpstarts, and many of the other > signals in the auto environment. FETS,CLIPPERS,Clamps? > Thank you in advance, > It is an open drain SSR. The automobile industry seriously needs to address providing DC to their customers. They need a better connector instead of the cig plug, and the DC should be conditioned. Ditto on transorb diodes.
From: Joel Koltner on 29 Apr 2010 13:14
<miso(a)sushi.com> wrote in message news:5c942ab3-7abe-4045-a98c-28b1f15ce440(a)k41g2000yqb.googlegroups.com... On Apr 26, 3:35 pm, Johnny5 <dirtylogicdesi...(a)gmail.com> wrote: > The automobile industry seriously needs to address providing DC to > their customers. They need a better connector instead of the cig plug, > and the DC should be conditioned. For that sort of thing the auto industry tends to follow rather than lead... there are a few cars out there (SUVs, I believe) that provide standard 120V AC outlets, and I wouldn't be surprised if sooner or later you see some USB (5V) connections (many 3rd-party stereos already have a USB port for playing back music from memory sticks, for that matter)... but what would the conditioned 12V standard connector be? The amateur radio guys like Anderson Powerpole connectors... |