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Original question:

Automotive buck-boost with 3V-14Vin

Wide input (automotive power) to 48V

steven heitbrink
Prodigy 230 points
Other Parts Discussed in Thread: LM5122

Hi,

I would love some advice on the best way to convert from automotive power (Vin=: 6V to 18V) to 48V. I am currently trying to figure out the output current, but currently lets assume it's at most 1.2A.

The issue with automotive is that it can see dip from a normal 12V down to 6V fairly quickly (<3ms). It seems to me that trying to use a current controlled boost converter from to converter from the automotive "12V" to 48V is a bit risky, and one might need to convert in at least 2 stages. Do you think this is correct? Or can modern controllers keep the output transient due to the input below a few hundred mV. 

Thanks

Steve H

  • 0
    TI__Mastermind 21720 points
    Hi Steve,

    Thanks for reaching out with your question.

    It is possible for boost controller to boost from the 12V automotive battery to 48V. I understand the cranking and the incurred voltage drop on the battery. If the loop is tuned correctly there is typically is little ripple on the output due to the line transient. Changing the output capacitance can help reduce the output ripple as well.

    I suggest using the LM5122 as the controller. Take a look at the reference design below. It is very close to your application requirements.
    www.ti.com/.../PMP10503

    Please let me know if you have any questions.

    thanks,

    Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 230 points

    Hi Garrett,

    Thanks for the response. If I want to have some idea what kind of output transient I will see, do you think I'd be able to use a transient SPICE simulation?

    It would be better if I could get a good ballpark of what the transient response on the output due to a sudden drop in the input before I try and produce this thing. It might be weeks, and a lot of work, before I could get a physical prototype together. 

    Thanks

    Steve H

  • 0 in reply to steven heitbrink
    Prodigy 230 points

    Hi Garrett,

    I don't know how much this is worth, but I did manage to throw together a SPICE simulation of the demo board that is getting hit by input transients. As you can see, the output moves around by less than 1% which is pretty good. I don't know how closely this tracks with physical reality, but it's at least encouraging.

    Thanks

    Steve H