LM2940-N: LDO for automotive

I found the appnote on automotive LDO design. I will go through it.

Hi Khoi,

take care, the supply voltage of a car battery comes from hell! There can huge positive and negative voltage spikes be superimposed on the battery voltage. And the load dump transient can be the super killer.

Find out which standards you must fullfill with your car voltage supply.

Kai

This is for trucks. I will need to check which standard and voltage. I was hoping I can find one from the appnote and put some tvs in the front to handle high surge

For 12V and 24V system and I believe they have to meet ISO 16750 for road vehicles.

Yes.

I have in my archive this here:

iso_7637_2.pdf

But this seems to be a bit outdated. Nevertheless, you will find some useful information in it.

Find out whether your supply must withstand test pulse 5a or 5b. 5a is very difficult to withstand. 5b is much easier!

Kai

LM2940IMP-5.0/NOPB (26V max)
TLE4275QKTTRQ1 (45V max)
I found these two potential candidate.

I assume you can protected using special TVS diode clamp. So maybe I should look for higher input LDO ?
Crank causes battery to go down to 6V, I would prefer a detection and reset the logic.
I need .750 to 1A peak LDO.

Hi Khoi,

first, find out whether yor supply must withstand the test pulse 5a or 5b. This is a huge difference!!

For a truck (24V battery) cold cranking can make the battery voltage go down to about 12...13V, at the battery terminals.

Kai

Hi Khoi,

Have you looked at TPS7A47-Q1? This is the closest part released to date that I am aware of to your application needs.

Very Respectfully,
Ryan

Yes, but it is overkill for us and it does not have reverse battery protection so I still need forward diode and TVS.

I only need less < 500mA, so I prefer something small in SOT223 package. Ideally with ENABLE pin since I need to reset under typical engine crank voltage at 6V.

I was thinking of using two LDO LM317 with the first one higher so that it can detect when power supply drop instead of enable pin.
This way I don't need to protect to enable pin of the LDO.

car battery -- [forward diode]--[TVS]-->LDO-8V -->LDO -->5V

I think I might use this TPS7B82-Q1 300-mA since both VIn and Enable can handle high voltage up to 45V for transient.

I need a threshold sensitive Enable, the TPS7B82 enable and disable range is too wide 0.5 to 2V.

There is so many of them, the search filter should be better. I found this with input voltage sense pin which should work.
TPS7A6933QDRQ1 for 150mA.

Is there something similar with higher output current 300mA or 500mA?

Hey Khoi,

We don't have any 40V+ VIN automotive LDOs with precision enable. Also, TPS7A69-Q1 does not have an enable feature.

When do you want the LDO to turn on/off? Have you considered pairing the LDO with a supervisor that monitors the input voltage?

~ Aaron