How to select step-down converter chip? [closed]

Question

I have some limited amateur-level electronics experience, but I'd like to try something new to me. I'm trying to design a small PCB that among some other fairly simple components will house a DC-DC step-down converter. I have tried to familiarize myself with the topic, and I understand that there are some precautions to take when designing the PCB. My main issue at the moment is - how do I actually select the chip to use? There are hundreds of different chips out there by various manufacturers, all with nice-looking data sheets, and besides some obvious criteria to rule out certain models (not enough current) - how should I narrow down the selection?

These are my requirements:

• convert 12-14 V down to 5 V, no step-up capabilities required
• current 1 A or more
• as few external components required as possible (PCB space is limited by external requirements)
• SOT or other SMD form factor that can be hand-soldered
• should be easily obtainable in smaller batches (10-20 units or so) by a hobbyist in central Europe
• does not require "exotic" external components
• pricing << 1 € per unit

I'm seeing a lot of pre-assembled modules, but I'd rather not use these - a) they are 10x as expensive, b) they take up too much space and c) there's no chance for me to learn anything new when using them...

What other factors do I have to consider when selecting a component? What is the best approach to narrow down the - to me - overwhelming set of components available?

Answer 1

If you are designing for commercial use and volume production the usual way is to just ask your distributor (eg. Arrow). Their sales guys will give you many options (logistics and availability are equally important as technical parameters). Of course they will move a finger only if you are thinking of mass production.

If you are designing for hobby use:

1. Go to chipmaker's website and use their part selector. Every manufacturer has one. Examples:

   • TI
   • Linear
   • ST
   • NXP
   • ON semi

2. Input your design requirements and narrow down until you have a manageable list of parts.

3. Look up these parts at the place you want to buy from (Mouser, Farnell, Aliexpress...) to see their availability and pricing.

4. Once you have a part selected, download and read its datasheet, especially the part with typical application and recommended layout. Check required external components.

5. Rinse and repeat

Answer 2

Many companys have a decent simulator for power designs. I use that to pick the parts and get the schematic working.

Off the top of my head I can list three I used:

• TI webench.ti.com
• Richtek richtek.transim.com
• ST also has one but I don't rember the link

Answer 3

You may not want to use a module, but those module designers have still done a lot of work for you: have a look at what modules are available that are in line with the specs that you need, and look into what components they're using. I see a lot of low-cost modules in the 1-2A range that are using LM2596 chips, for example. Looking into this chip, it seems to be appropriate for what you want (the 5V fixed output variant can be used with only 4 external components, for example, and handles up to 3A). The recommended price is outside of your budget, but I also see a lot of them available from budget suppliers that are within your budget (I think these may be selling up old non-RoHS stock, which may or may not be an issue for you).