PW-05 · Chapter 4 · Power Conversion
Choosing a buck regulator IC
What do you look at when choosing a buck regulator IC?
| Level | ●● onsite technical |
| Track | Power |
| Really testing | A complete checklist and the reasoning behind it. |
Full worked answer: in the book, page 92 — what to say first, how to explain it, the numbers worth quoting and the follow-ups. About the book →
Going deeper
Extra explanation that is not in the book: worked numbers, where people go wrong, and how to say it in the room.
Turning the checklist into decisions — three quick cases.
- 24 V industrial input with surges to 36 V: choose a 42 V or 60 V part; a 36 V-rated IC has no margin.
- 24 V → 1.2 V at 2 MHz: D = 5%, so the on-time would be 25 ns — below most parts' minimum on-time (50–100 ns). Drop to 400 kHz (125 ns on-time) or use two stages.
- A coin-cell or always-on product: quiescent current decides battery life. 2 µA vs 50 µA is months of standby.
EMI-driven choices. Automotive and radio products often keep fsw above the AM band (about 1.8 MHz or more) or move it with a sync pin. Spread-spectrum dithering lowers the peaks the EMI receiver sees.
Where people go wrong
- Choosing by the efficiency headline at one load point.
- Trusting θJA from the datasheet board — your board's copper sets the real temperature.
- Forgetting startup into a pre-biased output, or into a large load capacitance.
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