Automotive battery line filtering

[Thomas8607]

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-3

I 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/hQwzoZFDxo0

Thank you for helping

[nvmR]

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.pdf
https://www.ti.com/lit/an/snva717/snva717.pdf

[Thomas8607]

Thanks
Yes, i was seeing these, but in these circuits have nothing filter. Do i need to use filter? (L and C for EMI)

[Terry Bites]

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 TDK https://product.tdk.com/en/techlibrary/productoverview/cmf-for-power-supply.html

I found this EMI filter toolset on the Wurth site https://redexpert.we-online.com/emifd/en/#/filter-designer/params-form
And this one from TI InputFilterCalculator.xls (107 kB - downloaded 22 times.)

[chinoy]

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.

[Thomas8607]

I know this, but if i use more cap then will be  large transient. Because I use large inductor?

[Thomas8607]

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.

[T3sl4co1l]

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

[Thomas8607]

I think these will be my circuits.

Active rectifier control LT8672
LT8672 with emi
After
LT8653
Or Max20457, this is cheaper than LT8653
High efficiency on lower load

I think it well?
Both IC's have good efficiency on low load.
Thanks!

[T3sl4co1l]

I guess that's fine... it's an extra what $30 or more on the BOM though?  Is that really called for?

Tim

[Thomas8607]

I want a perfect circuit: D

2x Mp1584 ~$6 now
1x MAX20457 $4.49

+ L6872 ~ $6.42
Mosfet

I tried with ldo stabilizer in the first version, but those were warm.

[T3sl4co1l]

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

[Thomas8607]

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

[Thomas8607]

I did fix the first comment, the youtube link was wrong.
This is the dashboard
https://youtu.be/hQwzoZFDxo0
Nextion 7", esp32, ads7828, eeprom, 4 dual opamp, max9926, 4 optocouplers input, 3 optocouplers fet output, 2,42" OLED

[Thomas8607]

I've measured the currents. 5v 420mA, 3,3V 400mA

[T3sl4co1l]

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