TVS for Automotive application

[germano_a]

Hi everyone,

First of all, this is my first time in here.
Saw lot of peoples helping each other.
Then i decide to request some help.

My english isn't that great, so i hope i can be understood, at least.

I'm making an application that goes for a bus ( automotive, 24v )

It's a basic digital control for some I/O's with a uC.
It will drive an average of 1-2A and a maximum of 3A.

My concerc is about the protection and a suitable TVS.
I'm using a commom diode for reverse protection.
A Eletrol. Capacitor for filter and I want to use a TVS for spikes protection.
Is this one http://www.vishay.com/docs/88381/sm5a27.pdf ??

Is there anything else that i should take care??

Thanks for now!
Germano

[Janne]

Hi,

Here are some links I've collected to different appnotes regarding automotive enviroment.. Should give a good understanding at what to expect in automotive enviroment and some countermeasures against them.

http://www.industrologic.com/autotransients.pdf
http://www.industrologic.com/transient.pdf
http://www.maxim-ic.com/app-notes/index.mvp/id/760
http://www.eetimes.com/design/automotive-design/4011440/Automotive-environment-challenges-MCU-system-design-engineers?pageNumber=1
http://ecee.colorado.edu/~mcclurel/iap711.pdf

I've had good luck so far protecing my micros in automotive use by using series inductors, resistors and parallel capacitors + clamping devices. Though I've never built anything that would have required high amounts of "clean" power, so YMMW. I've always gone away with relays as the interface to the "nasty" world and been done with it.

It would be interesting to see what kind of front ends real professionals have designed for automotive use, when the BOM also needs to be minimized for mass production.

[Rudolfo]

Hi

You might also take a look at 24V interfacing at: http://ichaus.biz/mcu_interface

Enjoy the design!

[phil_jp1]

For 24V system breakdown voltage for TVS should be about 36V. At least that's what truck manufacturers stick into their automotive control modules.

[germano_a]

Thank you guys for ur repplys!

I'm still reading these articles, and im finding it very usefull!

After some research, here's a schematic wich I think that could be safe.



Any tip is appreciated. By the way, i have some doubt about the Fuse position,
should i put it before the varistor?

Thank you!
And sorry for my poor english again!

[qno]

Check out ISO_7637-2-2004.

These are all the test signals automotive components should survive.

[batteksystem]

Hi everyone,

First of all, this is my first time in here.
Saw lot of peoples helping each other.
Then i decide to request some help.

My english isn't that great, so i hope i can be understood, at least.

I'm making an application that goes for a bus ( automotive, 24v )

It's a basic digital control for some I/O's with a uC.
It will drive an average of 1-2A and a maximum of 3A.

My concerc is about the protection and a suitable TVS.
I'm using a commom diode for reverse protection.
A Eletrol. Capacitor for filter and I want to use a TVS for spikes protection.
Is this one http://www.vishay.com/docs/88381/sm5a27.pdf ??

Is there anything else that i should take care??

Thanks for now!
Germano

I use 36V TVS.

[halexa]

Hi,

I have used RBO40 from ST for 12V system, it has both TVS and Reversed battery diode in same package.
Don't know if they have similiar for 24V system since the reversed break dow of this is 24V.

http://www.st.com/content/ccc/resource/technical/document/datasheet/group1/e6/91/f3/cc/41/6e/4f/10/CD00001320/files/CD00001320.pdf/jcr:content/translations/en.CD00001320.pdf
 

[Psi]

I use ATV50C240JB-HF

5kW
24V working
26V min breakdown
39V clamp

Never had any returned units with blown TVS diodes since i moved to that diode.

(Had a couple previous generation units blow their TVS, those where 500W/18V diodes)

[Ian.M]

I use ATV50C240JB-HF

5kW
24V working
26V min breakdown
39V clamp

Never had any returned units with blown TVS diodes since i moved to that diode.

(Had a couple previous generation units blow their TVS, those where 500W/18V diodes)

I assume that's in a nominal 12V application?
As the charging system may well run at up to 2.4V/cell, (28.8V in a 24V system) and you need some margin for the working voltage, anything under 30V working is trouble waiting to happen . . .

[Psi]

Yep general 12V automotive system.

24V working voltage TVS is fine for that.

If you use anything larger you often run into problems with the clamping voltage being too high for your linear regulator. The ATV50C240JB is 39V clamping, so ok for most voltage regs which top out at 40-45V

[Ian.M]

The other issue is idiots jump-starting a 12V vehicle from a 24V truck. As the flat 12V battery will have a relatively high impedance, if the truck is running or its battery is much higher capacity, there is a high probability of your TVS seeing >24V.   If you *insist* on using a <30V TVS to clamp low enough to ease your regulator selection problem, you will need to use a TVS with a high surge rating and will need current limiting to stay within its SOA (i.e. a 50V polyfuse upstream of the TVS in your device's power feed) to prevent catastrophic destruction in the above scenario.

[sarepairman2]

or add a slower device with your TVS that can absorb more energy.

[batteksystem]

Hi,

I have used RBO40 from ST for 12V system, it has both TVS and Reversed battery diode in same package.
Don't know if they have similiar for 24V system since the reversed break dow of this is 24V.

http://www.st.com/content/ccc/resource/technical/document/datasheet/group1/e6/91/f3/cc/41/6e/4f/10/CD00001320/files/CD00001320.pdf/jcr:content/translations/en.CD00001320.pdf

Look nice, but a bit concerned on the reverse battery diode, at 40A, the drop is 1.9V which mean 76W loss.