Automotive (load dump) circuit protection  - Page 1
Forum section: electronics / projects

author: superKris
author_rank: Regular Contributor
timestamp: March 18, 2020, 11:42:16 am
content: Lately i have been reading a lot about automotive circuit protection. I spent many hours reading similar posts on this forum, studying datasheets, youtube movies, and reading articles. Still i have not been able to find a solution that I know will work.My situation:- The circuit contains a buck converter, LED, FET,s, caps and transistors that are connected to VCC. The maximum voltage the circuit can take is 24V.- The circuit is expected to use between 0,1 and 1A of current- It will be placed in a early 1980's van, so we can not expect any load dump protection to be present.So the solutions i found are:- TVS diode's- Crowbar circuit- dedicated IC's that disconnect the loadA automotive load dump (200V for 400ms) is extremely destructive. Normal TVS diodes and a FET in a corbar circuit will likely fail in a few ms. I would like to avoid dedicated chips as these are expensive and not as easy to get.So what real world options do i have here? The circuit is not critical, so i dont mind replacing a fuse if a actual load dump (battery disconnect) would happen. One of the circuits i need to protect actually already has a 2A blade fuse installed. I can do the same for the circuit i'm designing now, or i can use a PTC fuse.But i have my doubts a, for example,SMB sized TVSdiode rated at a clamp voltage of 24V and a peak current of 30A, will hold long enough to melt a blade fuse or trip a poly fuse. Same goes for a FET in a crowbar circuit.Adding a series resistor to the circuit isnt great either. Even with a way to low 1 ohm resistor i would dissipate a constant 1W at 1A current draw, and at 200V a 1 ohm SMD resistor might blow faster than the fuse i wil be using.I really dont know how to solve this problem anymore. Can anyone help we with some actual suitable parts and a circuit?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 18, 2020, 02:17:32 pm
content: 1A is low enough you might consider riding it through.I wouldn't use a TVS to blow a fuse, at least not one that small. Put an SCR in there to crowbar it. Also add series resistance if you can, to control peak fault current.By "van" do you actually mean something like a panel truck or semi? Most residential/commercial vans have been 12V AFAIK, so you shouldn't expect much over 60V load dump?Tim

author: DBecker
author_rank: Frequent Contributor
timestamp: March 18, 2020, 03:11:30 pm
content: Is this a one-off, or a production item?Does it need to meet a specification or just survive real-life conditions?Is the vehicle fully vintage, or has it been updated over the years? A semi-modern alternator voltage regulator will have load dump mitigation. There might still be a minor spike, but it won't be the full energy output of the alternator that a mechanical regulator would have allowed. Any regulator that is remotely modern will have benign behavior.The specifications aren't that difficult to meet. They allow fairly high series resistance (note that you get to pick some of the system parameters). What might be challenging for non-automotive parts is that they allow for 24V jump starts e.g. brief but continuous 28+V system voltage. While this is almost an obsolete scenario (tow/service trucks now use jump start boxes rather than long cables to doubled-up batteries), it requires TVS protection to be in the 33V-36V range. Your parts need to support 35V or 40V excursions without damage.

author: Yansi
author_rank: Super Contributor
timestamp: March 18, 2020, 04:17:29 pm
content: Refer to the LV124 standard for details about requirements on voltage input to devices.Note that some car manufacturers may use their own slightly modified versions of this standard.But 200V load dump?

author: superKris
author_rank: Regular Contributor
timestamp: March 18, 2020, 05:10:01 pm
content: Thank you all for your replies!Quote from: T3sl4co1l on March 18, 2020, 02:17:32 pmHow do you mean 1A is low enough?I dont see how this is related to the load dump spike.Is there a significant advantage to a SCR compared to a FET? And what why is a SCR better for popping a fuse than a TVS? I dont see that much difference in shot term max current when i look into the datasheets of similair sized components.Quote from: DBecker on March 18, 2020, 03:11:30 pmIn my case its a early 80's VW LT camper van. Not much electronics in there except for wat i already build in. The van already has a early prototype version of my circuit that runs of the AMS1117 regulator on a arduino. I think it has a single series diode and and a 5A fuse for protection, but that's about it. I'm doing a V2 with an actual PCB and a improved circuit. This is mainly a one-off for myself, but i'll be making a few extra to sell/give away to friends. If it works well, and people are interested i might start selling them. If that doesn't happen i will be making it open source. That is why i'm looking for a affordable but robust solution. My van might be very old, but others may want to install in a even much older camper vans.I dont need it to support 24V systems. 12V is fine. I'm designing everything to work in the 10 tot 16V range. If a fuse pops at 17V that is fine with me.Quote from: Yansi on March 18, 2020, 04:17:29 pmThanks for sharing. I'm sure there are many standard and not all of them require a full battery disconnect lead dump. Lets be honest, this very rarely happens and when it does happen, its likely that many other electronics die too.However, i am trying to make it as robust as i can without making things to complicated of expensive.

author: Yansi
author_rank: Super Contributor
timestamp: March 18, 2020, 06:48:04 pm
content: If you want to design for bullshit that won't ever happen, I'd recommend following this:http://www.ti.com/lit/an/snva717/snva717.pdfLV124 is currently what is used by the majority of car makers (Japanese folks are one of the exception), with or without slight modification to some requirements or values. None of the LV124 tests require 200V bullshit as far as I can tell (currently designing stuff for Daimler at work and do not remember even mentioning input should withstand 200V pulse). That is not happening, easily, without doubling the BOM cost.We use just appropriately selected TVS, series connected diode and appropriately sized automotive LDO (42V rated).It is likely your bigger enemy will be functional status requirements at low input voltage. Some stuff needs to work reliably even at pretty low input voltage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 18, 2020, 09:37:26 pm
content: Quote from: superKris on March 18, 2020, 05:10:01 pmTakes two to cause a problem, a source and a load. If you simply put an LDO in front of the load -- one that can handle the voltage drop and energy dissipation -- you'd be set, nothing even happens, it just completely rides through it.Easiest way to do this is a small zener shunt regulator, plus depletion MOS follower. At nominal voltages, the zener isn't in breakdown, so the DMOS gate is at Vin, and it's turned on (DMOS is "normally on" and takes negative Vgs bias to turn off). As input rises above Vz, gate voltage gets clamped, and source voltage follows maybe a volt or two higher (depending on load).Or a PMOS with control circuitry. Or a proper LDO, which does the same thing, but has a proper voltage reference -- not that you need an accurately clamped voltage, that's just a bonus.If your input peak truly is 200V, and the load voltage is maximum say 18V, and load current maximum 1A, then the limiter would have to dissipate (200 - 18V) * 1A = 182W peak, for a pulse width of some hundred milliseconds. (It's an exponential decay rather than a square pulse --not as bad as it sounds, but it's still a sizable slug of energy for semiconductors to handle.)You'd probably be looking at one or a couple TO-220s on heatsinks, or a TO-247 or the like.If the peak voltage, or the load current, is lower, this looks pretty good.A switch is definitely an attractive option for higher power levels. PMOS, with less control circuitry, would be fine here. 200V 5A something or other, I suppose. And there are controller chips if you don't mind paying the premium.Note my first reaction is effectively to increase the load impedance. This is because the nominal load impedance is already higher than the load dump impedance (a few ohms), so we will absorb less than full power already, and can stand to absorb even less by increasing the impedance further. (Using a hand-waving meaning of impedance, such as the average: compare e.g. 12V / 1A = 12 ohm nominal equivalent, versus at full ride-through, 200V / 1A = 200 ohm equivalent.)Going the other direction, sure, you can absorb the dump to some extent or another -- but you will dissipate far more power, unless you shunt it into a very low impedance (< 20mohm?) so that most of the power is dissipated by the alternator itself.Which...Quote...If you choose a FET with low enough resistance, yes, that is still fine. You will need to sink some hundreds of amperes to clear a fuse (again, potentially less if you add series resistance to limit short circuit current), which is quite demanding for a MOSFET, but fairly pedestrian for even a D(2)PAK sized SCR.The SCR doesn't need any additional circuitry, it's a latching device all by itself (just use a zener to set the trigger threshold); a MOSFET needs a latch, and also something to store drive voltage.Note that, if you use ashunt regulatorrather than a latching crowbar, then you need to bear peak current times nominal voltage drop -- you're lowering rather than raising the equivalent load resistance, and you're not lowering it by very much so it better be one hell of a beefy shunt. Dropping in one of those fat ass TVS diodes looks very attractive versus cooking up a shunt regulator.QuoteThen that'll most likely be 60V load dump. Not nearly as scary. A lot of parts are available to handle it, too! Might just change that '1117 and be done.Is itreallya 1A load? That's a LOT of Arduinos.If you have, like, a motor, or some lights, or whatever, something dumb on there, and that's what's drawing most of the load current? You may find it helpful to separate it. Motors aren't going to give a shit about load dump, they can use raw 12V, who cares. Lights will glow brightly and probably not die, or can be designed to handle it more gracefully with less effort. Meanwhile, that Arduino using, whatever, 3.3 or 5V at some 10s of mA, a slightly beefier regulator isn't going to mind passing that while momentarily dropping 50V.Lots of design opportunities, keep your mind open to them. No need to hide everything inside a black box!QuoteFor one-offs, that are neither terribly expensive, nor terribly mission-critical, it's hard to justify anything beyond basic fire protection (i.e., it shouldn't burst into flames under these conditions), really. You may find that "robust" and "complicated/expensive" just happen to intersect at the point of zero additional design effort.Tim

author: max_torque
author_rank: Super Contributor
timestamp: March 19, 2020, 08:00:58 pm
content: When designing for a modern vehicle with lots of electronic units, my no1 rule for surviving load dump and voltage excursions is to be the last to jump! Ie, if there are twenty other units on the power bus that fall down first (ie has TVS diodes that clamp away the excessive energy in the load dump) then my unit is going to have the easiest time and be most likely to survive! That means using a TVS diode of the highest breakdown voltage i can get away with, and that depends on the series impedance in the unit and its supply (the lower the necessary impedance, the larger the clamping current and the higher the TVS voltage as it carries that current, and hence the higher the peak of the clamped voltage) and the capability of my unit to withstand that higher voltage. Most automotive voltage regulators will withstand around 60v peak for short term spikes, so i use a TVS that clamps the full fault current at around 58 volts, which for a very low impedance device and supply (required by units that must pull high current during normal operation) means a TVS nominal breakdown at around 36V.As you already have a buck converter, why not just swap for one that can withstand a higher input voltage? There are plenty that can run at 50 to 70Vdc continuously, and if you only pull a small current from your supply, you can add a small amount of robust resistance (i use 5w wire wound resistors) upstream of that convertor and your clamping TVS to limit fault current. Depending on the output voltage of your buck, you can work out your worst case voltage head room and see if adding resistance is viable.I typically use vishay SM8 TVS diodes that are rated at very high instantaneous peak dissipation (3.6kW !!) when properly heat sinked to a decent area of pcb etchttps://www.mouser.co.uk/ProductDetail/Vishay-Semiconductors/SM5S36AHE3_A-I?qs=sGAEpiMZZMvxHShE6Whpu0CRSaykhk%252BlX7EObMWzxGA%3DI also try to use some series inductance to take the peak off very short term voltage spikes, but be careful about forming a tank circuit with any capacitance in your unit of the supply!

author: David Hess
author_rank: Super Contributor
timestamp: March 20, 2020, 05:42:17 am
content: Quote from: superKris on March 18, 2020, 11:42:16 amCombining these two may be acceptable but require a fusible link or fuse to blow which might as well be considered a failure.QuoteThat is how I have done it in the past; a high voltage series transistor can block the overload easily while having very low voltage drop under normal loads. If a continuous overload is a possibility, then a shutdown circuit or foldback current limiting should be included to protect the transistor from excessive power dissipation.

author: dario200
author_rank: Newbie
timestamp: May 13, 2021, 10:49:50 pm
content: Hi! Have you solved this? I'm in the same situation and I don't know what circuit to use. I have considered using the LM5060-Q1, also the discrete solution with a TLV431 but I'm not yet convinced. May I ask what have you finally used?Thanks in advance.

author: james_s
author_rank: Super Contributor
timestamp: May 13, 2021, 11:18:10 pm
content: About 10 years ago I repaired the ECU in a late 80s VW. It had a 5V 3 terminal regulator that IIRC was just a 7805 in a fairly conventional configuration, I don't remember seeing any exotic protection circuitry. I don't think load dump is really a thing in modern cars, and by "modern" I mean built in the last 40 years. Now if you're making electronics you intend to use in a completely stock 1960s car with an electromechanical regulator then you could have an issue.

author: floobydust
author_rank: Super Contributor
timestamp: May 14, 2021, 02:12:38 am
content: I say you don't design for "load dump" because it is very costly to deal with the high energy involved, it only happens under one failure condition (car battery gets disconnected, corroded terminals) and modern alternators clamp it to about 40V, and ECU's are only rated to handle it for one or two load dumps before the electronics is damaged.If I'm protecting something expensive, I use brute force massive 6,600W TVS popular in the automotive industry VishaySM8A2740V at 87A. There is a smallerSM5A27.You really need some line resistance like from the wiring+fuse, you'll get an ohm or more, to lower clamping currents which permits a smaller TVS.Ride-through surge protectors didn't cut the mustard for me, I abandoned them.LT4356et al because most put the pass-transistor into a linear mode during the surge and they quickly roast due to inadequate SOA. Other IC's will just cut power off for the few hundred msec which works OK. But it's still a lot of parts and cost and complexity.bit more hereTransient Voltage Suppressors (TVS) for Automotive Electronic Protection

author: Analog4
author_rank: Contributor
timestamp: May 17, 2021, 12:21:25 am
content: One could use a fancy IC, like a LM7480, for load dump protection. It really depends on how much voltage drop you can tolerate for protection. Series resistance to any clamp (such as a TVS) will limit the power that needs to be absorbed by the clamp (less current and voltage - smaller clamp). If one can tolerate series diode voltage drop, a series diodes can help with reverse protection.There is a nice article here:https://www.ti.com/lit/pdf/slyt802Datasheet for LM7480-Q1 Ideal Diode Controller with Load Dump Protection:https://www.ti.com/lit/gpn/lm7480-q1Also a note, Basics of Ideal Diodes:https://www.ti.com/lit/pdf/slvae57The Littlefuse TVS App note is attached.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 17, 2021, 01:09:13 am
content: An application of the power transfer theorem, by the way:Load dump is usually specified as voltage in excess of nominal, supplied through a nominal source resistance Rs. (At or below nominal voltage, a diode supplies ~unlimited current from the battery, or the regulator behaves normally or whatever.)If your equivalent load resistance R_L is higher than Rs, consider ride-through methods. You will dissipate less power by dropping the excess voltage.If lower, consider shunting (TVS or other) methods. You will dissipate less power by shunting it.This is still quite a lot of power and energy (hundreds of watts for hundreds of ms), so if you're in the middle case there, it's a tough job no matter how you cut it. Consider increasing the operating range of your device, or adding a shutoff mechanism.And, the exact crossover point varies, because of that catch, of where nominal voltage pulls in. (You can't pull down an 18V overvoltage to 9V, if current rises sharply below 12V...) At least, in the lab test -- I don't know if that particular nonlinearity applies to the real deal as well.If you're very far from the middle case, however, your job is proportionally easier -- ride-thru might go from challenging (given packaging, power dissipation and cost limitations), to downright trivial (e.g. a single DMOS for R_L >> Rs, or just keeping the thing in operation for R_L << Rs).So you can use this to get some idea of which strategy is likely to pay off the best, and how to compare them.Tim

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 17, 2021, 02:20:02 am
content: Trying to short circuit a load dump is probably not the greatest idea of this century.Some time ago I had a look at a few application notes for load dump protection, and they had a reasonably high voltage MOSfet in series with the "gadget" and they just turn off the FET if the input voltage gets too low. In combination with some filtering to prevent false triggering and some extra circuitry to ensure that the voltage after the Fet rises slow enough for the filtering, comparator and FET to have some reaction time.A quick search:https://html.duckduckgo.com/html?q=automotive+load+dump+protection+application+noteGives:https://www.ti.com/lit/an/snva681a/snva681a.pdfwhich has the circuit attached below.

author: Scrts
author_rank: Frequent Contributor
timestamp: May 17, 2021, 02:34:12 am
content: Also see here:https://www.ti.com/tool/TIDA-01167In general, how likely you'll get load dump?

author: floobydust
author_rank: Super Contributor
timestamp: May 17, 2021, 03:54:54 am
content: Jr. Engineer designs in a load dump protection circuit from the datasheet, in a 24V truck product usingLTC4356S-1 surge stopper.Full production is going and a couple weeks later the phone starts ringing, units are failing out in the field. Dead surge-stopper IC substrate cooked, and mosfet sometimes.It crosses my desk, and I figure out there's no coverage for -ve transients (which are the most common) unless you use (two) back-back mosfets and a TVS, and Jr. did not include that circuit. The MOV he selected is 0805 "automotive" lol.ISO7637-2 harsher than ISO 16750 (24V systems) is -450V to -600V and +150V to +200V spikes, load dump 123-173V. None of these datasheet circuits are tough enough.Point is, designing something by copying the datasheet and with good intentions is not going to work.You have to test a design, and automotive transient and load dump generators are extremely expensive- rent them e.g. olderLD 200N.Note the load dump standards vary widely between car makers and I see Ford is only 60V/0.5 ohm so they must be counting on the alternator's zeners.It's possible to hack something together as well. But you still have to know what you are doing, it's not easy and at the end of the day, I find load dump only happens when a car/truck is old and close to the scrap yard, bad battery terminals and wiring.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 17, 2021, 04:40:07 am
content: Quote from: Doctorandus_P on May 17, 2021, 02:20:02 amHow so? They sell quite a lot of TVS diodes forexactly this purpose-- someone must think it's useful!QuoteOh yeah, that thing.Needs quite a bit of work to handle fluctuations and transients, but the general idea is fine, switching off the load I mean, it's a fine way to dodge the brunt of a surge.Tim

author: Terry Bites
author_rank: Super Contributor
timestamp: May 18, 2021, 01:40:19 pm
content: ST and others make just the the jobLDP01-xxAYhttps://www.st.com/en/protection-devices/ldp01-26ay.html

author: kellogs
author_rank: Regular Contributor
timestamp: October 07, 2022, 11:12:44 am
content: Quote from: max_torque on March 19, 2020, 08:00:58 pmIs a cap alone not enough for the same purpose of taking peaks off of very short transients ?Such as this a 100nF X7R dielectric MLCChttps://www.powersystemsdesign.com/articles/transient-protection-solutions-in-automobiles/22/13262

author: mr ed
author_rank: Regular Contributor
timestamp: October 08, 2022, 02:55:56 am
content: A long time ago the company I worked at designed for a negative 300 volt spike and a positive 65 volt spike. I don't remember the joule level but was at least over one j. Enough to warm up the protection a bit. Transzorbs were the solution then. Route the excess current to one ground point, no ground loops please. 12 volt old school cars.

author: Psi
author_rank: Super Contributor
timestamp: October 08, 2022, 05:28:56 am
content: I've had well over 1000 devices in the automotive field for many many years and none have been returned with exploded TVS diodes. (except some earily prototypes that had tiny ones).For protection the product just has a 5kW 24V TVS diode (38V clamp) on the PCB between VBATT and GND.The VBatt feeds two things on the PCB- A 5V VReg which is also automotive rated and also has some level of 60V transient protection itself.- An automotive rated high-side integrated driver chip that PWMs a 10A load at 100hz.

author: jonpaul
author_rank: Super Contributor
timestamp: October 08, 2022, 06:30:13 am
content: Hello faced this exact issue long ago, a transient absorbing diode can work.We used the Motorola MR2525 diode, specifically designed for alt load dump protection, a very large die transient protective Zener, specified for that use.This was circi 1986-1989, modern equivalents existhttps://datasheet.datasheetarchive.com/originals/distributors/Datasheets-3/DSA-44077.pdfhttps://pdf1.alldatasheet.com/datasheet-pdf/view/223386/DEC/MR2525.htmlThe alt load dump is 70V or more and jules of energy, stored in lams of the alt at field turn off.Jon

author: Psi
author_rank: Super Contributor
timestamp: October 08, 2022, 06:39:13 am
content: Quote from: jonpaul on October 08, 2022, 06:30:13 amSimilar to the ATV50C240JB-HF I use.110A on the MR2525 vs 128.5A on the ATV50C240JB-HFMR2525 has a bit more non-repetitive surge current though, 600A vs 300A on ATV50C240JB-HF

author: jonpaul
author_rank: Super Contributor
timestamp: October 08, 2022, 07:34:12 am
content: See also MR2535, we used two in series for a 28V avainoicas bus.SMD modern equiv are made, see Protek, etc.Jon