Automotive battery line filtering - Page 1
Forum section: electronics / beginners

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 09:53:12 am
content: Hi there!I'm working on an automotive project. I've planned this circuit for filtering.After the filter circuit is two dc-dc converters(MP1584 ic's) for 5V(Nextion display, max9926 ic) and 3,3V (ESP32, eeprom, giroscope, ads7828 adc,oled display)I would like to make it work well.I have some questions:- Do i need for me the inductor-capacitor circuit?-Do i need to use this protection circuit?- Do i use this maxim ic?https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/MAX16127.html/product-details/tabs-3I want to make sure that the dashboard does not restart when starting the engine, and to be well protection circuit.This is my project:https://youtu.be/hQwzoZFDxo0Thank you for helping

author: nvmR
author_rank: Regular Contributor
timestamp: April 10, 2022, 10:37:06 am
content: Hi Thomas,Welcome to the forum!TI has a bunch of app notes regarding automotive use cases - they can be helpful.https://www.ti.com/lit/an/snva681a/snva681a.pdfhttps://www.ti.com/lit/an/snva717/snva717.pdf

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 11:49:50 am
content: ThanksYes, i was seeing these, but in these circuits have nothing filter. Do i need to use filter? (L and C for EMI)

author: Terry Bites
author_rank: Super Contributor
timestamp: April 10, 2022, 12:22:43 pm
content: It seems you've done your homework there, adding damping to your LC filter a good idea. You do need to know your enemy,ie any particular signal frequncies that need particular attention.I think feeding two DC-DC converters from a common LC filter might be a problem. Its possible that there could be some unexpected interaction between the switchers.I'd use a single transient and reverse polarity section and feed two separate filters from there.It can be avantageous to get some degree of AC isolation from the car's ground and local circuit ground by inserting a common mode choke befor the LP section.See this informative page from TDKhttps://product.tdk.com/en/techlibrary/productoverview/cmf-for-power-supply.htmlI found this EMI filter toolset on the Wurth sitehttps://redexpert.we-online.com/emifd/en/#/filter-designer/params-formAnd this one from TIInputFilterCalculator.xls(107 kB - downloaded 43 times.)

author: chinoy
author_rank: Regular Contributor
timestamp: April 10, 2022, 12:28:12 pm
content: I found that the simplest solution to preventing stuff from rebooting in automotive stuff was to just keep increasing the cap value on the power rail. And a TVS diode to clean up any noise with a MOV. On my ECU I found that a 25v 2200 mfd cap worked. The only problem with the TVS diodes is that sometimes when they fail they go to fully short.

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 12:37:15 pm
content: I know this, but if i use more cap then will be large transient. Because I use large inductor?

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 12:50:14 pm
content: I would need a circuit diagram that is already in use, either an ecu or other mcu circuit. I'm looking for a sure solution.If anyone has this possibly.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 10, 2022, 01:05:33 pm
content: The filter is a good idea, yes.Hmm, do you really need 3A converters for that amount of stuff? Seems like a few hundred mA would do. The downside is low efficiency, running 3A converters at light load -- if that's the case. May also be audible noise (due to burst mode operation). If the 3.3V load isn't much (under 500mA), I'd also consider using an LDO, so only the 5V converter -- also saves cost and space.Having operation down to 6 or 7V or so, will keep it operating under cranking conditions. If you need more, a hold-up capacitor may be desirable; but mind that keeping it up for more than some ms takes quite a lot of capacitance, and then you might want a circuit to limit its charging current, etc. At which point you can use basically as much as you want, throw in supercaps or a battery for all that matters.Tim

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 06:36:44 pm
content: I think these will be my circuits.Active rectifier control LT8672LT8672 with emiAfterLT8653Or Max20457, this is cheaper than LT8653High efficiency on lower loadI think it well?Both IC's have good efficiency on low load.Thanks!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 10, 2022, 07:16:58 pm
content: I guess that's fine... it's an extra what $30 or more on the BOM though? Is that really called for?Tim

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 07:30:37 pm
content: I want a perfect circuit: D2x Mp1584 ~$6 now1x MAX20457 $4.49+ L6872 ~ $6.42MosfetI tried with ldo stabilizer in the first version, but those were warm.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 10, 2022, 07:39:46 pm
content: The perfect circuit is satisfactory to user expectations (performance, cost, etc.), cheap to produce and fast to design."Warm" sounds rather boring. "Painfully hot" might be a cause for concern? I don't know.You haven't given any supporting info that can allow us to gauge the suitability of these options, so it's all up to you.Tim

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 07:57:10 pm
content: When I planned to part of the power supply, everyone talked about LDO stabilizers 😀It also works on the MP1584, no voice, does not heat.But if I got better I'll buy it. I'm making the dashboard for sale, not to myself. I would like to work for sure for a long time.Thank you

author: Thomas8607
author_rank: Contributor
timestamp: April 10, 2022, 08:09:24 pm
content: I did fix the first comment, the youtube link was wrong.This is the dashboardhttps://youtu.be/hQwzoZFDxo0Nextion 7", esp32, ads7828, eeprom, 4 dual opamp, max9926, 4 optocouplers input, 3 optocouplers fet output, 2,42" OLED

author: Thomas8607
author_rank: Contributor
timestamp: April 12, 2022, 05:57:27 pm
content: I've measured the currents. 5v 420mA, 3,3V 400mA

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 12, 2022, 06:16:08 pm
content: That sounds quite modest. How about a 5V >1A regulator and, either a 3.3V LDO (1.7V * 0.4A = 0.68W isn't too bad) or a smaller switching regulator (5V input)? Think I would prefer using two different switching regulators, especially if the startup between 3.3/5V needs to be synchronized in some way, but anyway, using two separate regulators (from 12V) isn't bad either (and there are types available that can give synchronized startup).Tim