+5V to 42V step regulator design

Dear Youhao Xi,

Thank you for getting back to me. The LM5155 looks like it might be a bit "over kill" for my design. Also it is a little difficult to know what the Approx. PCB area might be as in the data sheet for the design e.g. (. Design Example Parameters) it only give the option for 24V and I will need also -ve supply as well. 

I did did a little bit more research and narrowed down my requirements a little more :-

I need 2 output supplies between 0.75A - 1A. I could be I could go a little lower than this but not much. I think I am going to have a total Max PCB area of 400 mm squared (when using both sides of the PCB). My Max input voltage is +5V. I am looking at +/-12V or if I can find something +/-24 V would be better. I doubt +42V & -24V outputs are not going to be even an option for the area I have (even though this would give me the most flexibility in my design !). I have been sorting through some options offered by Analog\Linear Devices and the best thing I have found so far is the the LT8582 1.5MHz, 5V to ±12V Boost and Inverting Converter (found in the Typical Applications). I did a basic calculation of PCB area just used by the components and I think the area comes out to approx 240 mm squared. 

Do you know of any better than this ?

 Thanks in advanced 

Shmuel 

Hi Shmuel,

Not sure about your efficiency requirement.  The LM5155 can implement +/- dual outputs in a sepic, or flyback with dual output rail.  The main issue is not the controller but the magnetics which fits in your pcb form factor.   If you can contact a TI sales personnel or FAE in your region, they can help you to get a reference design.  Like I recommended earlier, the LM5155 (2mm x 3mm) should be the best way to go. You are talking about >50W (42V or 12V, Q1A). Not understand why you said the LM5155 is an overkill. 

Thanks,

Youhao

Hi Shmuel,

Can I assume the issue is resolved?  Let me close it here but you can re-open it by adding a new post.  If you have any updates, please let us known.

Thanks,

Youhao 

Dear Youhao,

Thank you for your reply.

Could you please tell me what would be the Max Current(for each supply) that the LM5155 in a dual configuration +/- 12V c.f. +/-24V would be ?

Best regards

Shmuel 

Dear Youhao,

Thanks for getting back to me ! 

We need a a max current of 0.75A - 1A for either solution. Do you have something else that might work for either +/-12V or +/-24V that will give me a smaller total PCB area ? 

Best regards

Shmuel 

Any updates ?

Thank you for getting back to me.

I need +/-12V 0.6A - 0.8A (or if possible +/-24V 0.6A - 0.8A - but I doubt I will manage this much in my small PCB area !). So I think LM5155 will not fit into my limited PCB area - I don't need "1.5A for your +/-24V, or up to 3A for your +/-12V" - do you have anything more suitable for my design ?

So far the initial layout for the LT8582  gave me approx. a Total of 330 mm^2 (on both sides of my PCB - but in the propoer design I am sure it will be a little bigger than this) but it would be great if I could find a something a little more compact ?! Note the LT8582 design gives me +/- 12v with a max of 600mA for each supply ! Do you have anything possibly that can give me a smaller area with the same spec or better ?

I think that we could manage with a design < 20W. 

For the time being we can manage with the +/-12V @ 600mA design given by the LT8582 - for which we at least have an idea of how much PCB are might take.

It appears that a design using  LM5155 will not fit into the PCB area that we have 

Are you able to provide a design e.g. using your suggested TPS55340 to give both +12V & -12 supply so that I can get an idea of the PCB area such a design would take and the current it could provide ?