Automotive protection (ISO16750) for a low current PCB board - Page 1
Forum section: electronics / projects

author: jrgandara
author_rank: Contributor
timestamp: January 18, 2021, 03:12:07 am
content: Hello guys! Needing some advise about a subject I don't have experience and hope someone with expertise in this area could help.I was asked, sometime ago, to make an electronic module for use together with GPS modules in cars by a customer. I did the module and it is working just fine. We have about 10.000 running without problems. Now a new costumer of this customer wants to buy the solution but wants the module to meet the standard ISO16750. I did a little research on the subject and looks like all solutions I find cost too much and uses too many components. The examples I found normally protects high current circuts. My module is very simple and cost only a few bucks, so is very price sensitive. I have found TVS costing more than my entire module! So I would like to hear from you if is possible to protect this module being a cost efective or if is a impossible mission. I hope that is possible because it is very low current.The VCC input of the module goes to a 78L05 regulator which drives a low cost little 5V MCU. There are only 2 digital ports which interfaces with the digital ports of a GPS module. I hope these two digital ports don't need extra protection since goes between the two low voltage devices.Current consumption of the module at 14V (car battery) is less than 3mA. The PCB size is only 30mm x 14mm.Any suggestion will be appreciated.Thank you in advance.

author: Niklas
author_rank: Frequent Contributor
timestamp: January 18, 2021, 01:46:52 pm
content: One thing you can start with is to ask the potential customer about which classes and performance criteria that is applicable. Some customers have all the details ready,but some have no clue and just asks for something that looks good in their specs."Must pass EMC test" is a classic. Yes, but at what levels?16750-2 defines different tests, waveforms etc, but it does not mention what is OK/NOK. For instance the performance criteria ranges from A (no impact from disturbance) to E (destroyed, need replacement).

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 18, 2021, 01:48:17 pm
content: Add a series resistor on the input along with a zener diode just before the regulator. The resistor is sized for proper operation at minimum input voltage and the zener should be something like 18V.

author: jrgandara
author_rank: Contributor
timestamp: January 18, 2021, 02:32:25 pm
content: When my customer asked me about that I contacted his costumer for more details. They don't know what they are demanding, just someone told them about these ISO standards and they asked for. I think if I manage to implement this 100V/400ms pulse protection will be a good think for my product. So I will try to come up with some degree of protection.

author: jrgandara
author_rank: Contributor
timestamp: January 18, 2021, 02:36:25 pm
content: Thank you! I will definitely try this approach. Now I need to make a circuit to generate that kind of pulse for the tests.Anyone have a schematic for a pulse generator like this?

author: IDEngineer
author_rank: Super Contributor
timestamp: January 18, 2021, 08:59:06 pm
content: Quote from: jrgandara on January 18, 2021, 03:12:07 amThe 78L05 itself has a quiescent current of 3-5mA (source: TI spec sheet). Must not be much other circuitry on your board.

author: jrgandara
author_rank: Contributor
timestamp: January 19, 2021, 12:55:14 am
content: There are only few parts. It is a small MCU in sleep mode all the time and eventually it will send a digital pulse. The current in standby is 2.277mA and a maximum about 5mA when pulsing.

author: Niklas
author_rank: Frequent Contributor
timestamp: January 19, 2021, 06:12:55 am
content: As the pulse 5 is relatively slow, it could be approximated with 2 power supplies in a wired-OR configuration wiith diodes. One supply provides the nominal voltage and the other one can be toggled on-off rapidly, using the output enable switch, to create a pulse. Use an oscilloscope to verify the pulse length and amplitude.The method works for input protections that are not just a TVS trying to clamp the pulse energy.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 19, 2021, 07:37:25 pm
content: Just a bit of warning: ''meet the standard ISO16750'' might mean certified according to that standard. Certification will have to be carried out in an accredited lab wich has to perform the necessary testing. Just that will cost $$$! I mean several thousands, at least. Sure you do want to pre-test, before going to the lab, but that will not count, from a certification perspective.These labs work with good and expensive equipment, generally. Making a pulse generator with those exact characteristics might not be trivial.

author: jrgandara
author_rank: Contributor
timestamp: January 21, 2021, 12:16:35 pm
content: I have an 1:1 120V transformer in hand. I'm thinking in retifiy the output and stabilize at 104V DC. With a mosfet switch controlled by an Arduino I can simulate this pulse. Let's see if it works.

author: jrgandara
author_rank: Contributor
timestamp: January 21, 2021, 12:31:45 pm
content: I just talked to the customer and he was clueless about all this 17650 ISO classes of specs. Looks like someone just tip him to ask for this standards without realizing if a product this simple and cheap can meet all these standards without becoming economically unviable.Thank you all for the valuable help.