Buck Converter Basics: Choosing Between Synchronous and Asynchronous Buck ICs
The buck (step-down) converter is the workhorse of modern electronics: 12 V to 5 V, 5 V to 3.3 V, 3.8 V to 1.8 V — nearly every board has at least one. Choosing the right buck IC starts with one fork: synchronous (integrated high-side + low-side MOSFETs) or asynchronous (high-side switch plus external Schottky). Feeling Technology's FP61xx series spans both, and we stock them as an independent distributor.
Synchronous buck: efficiency without a Schottky
Synchronous buck ICs integrate both MOSFETs and actively rectify the switching node, eliminating the diode drop. At low output voltages (1.0–3.3 V rails for MCUs, memory, radios) the diode loss in an asynchronous design can dominate, so synchronous conversion wins clearly. Feeling's synchronous parts include FP6165ADXR-G1 (SOP-8(EP)) and FP6188XR-G1 — compact, integrated solutions for point-of-load rails.
Asynchronous buck: simplest and cheapest
Asynchronous buck ICs pair the internal high-side switch with an external Schottky diode. At higher output voltages the diode's relative loss shrinks, and the part cost drops. The family covers FP6195LR-G1 (SOT23-6, minimal footprint) and FP6150BXR-G1 / FP6151XR-G1 (SOP-8(EP)) — good candidates for 12 V/24 V auxiliary rails, bias supplies and cost-driven consumer goods.
Head-to-head
| Criterion | Synchronous (FP6165/FP6188) | Asynchronous (FP6195/FP615x) |
|---|---|---|
| Efficiency at low VOUT | High — no diode drop | Lower — Schottky drop constant |
| Efficiency at light load | Depends on mode (may need diode emulation) | Simple, predictable |
| BOM | No Schottky needed | + one Schottky |
| Best fit | 1–3.3 V point-of-load rails | Higher VOUT, cost-sensitive rails |
Layout and component notes
- Minimise the hot loop: input capacitor → high-side switch → low-side switch/Schottky → inductor. Every mm² of loop area adds ringing and EMI.
- Size the inductor for ripple current (typically 20–40% of load) and check saturation at maximum load and maximum temperature.
- For SOP-8(EP) packages, the exposed pad is the thermal path — pour copper underneath and stitch vias.
- Feedback resistors: place close to the FB pin and route away from the switch node to avoid offset errors.
Pairing with the rest of the power tree
Most boards combine buck and boost stages — a boost from the battery to a 5 V bus (see our boost topology guide) and synchronous bucks from 5 V to the logic rails. For battery charging before the power tree, see the charge management guide; for LED loads, see the constant-current driver guide.
Sourcing
- Stock and date codes for all parts above are listed under Power Management Chips.
- Upload your BOM for a complete power-tree quote, or contact us for volume pricing.
Questions & Answers
When does a synchronous buck clearly beat an asynchronous one?
At low output voltages (roughly below 3.3 V) and moderate to high load current, the Schottky's constant forward drop makes asynchronous efficiency significantly worse. Synchronous rectification removes that loss.
Is an asynchronous buck ever the better choice?
Yes — for higher output voltages, very cost-sensitive products, or light-load-dominated applications where its simplicity and low IC price win.
What does the (EP) in SOP-8(EP) mean?
Exposed Pad: the die paddle is solderable on the package bottom, providing a low thermal-resistance path into the PCB copper. Always solder it to a copper pour.
Can Jingteng Electronics supply the FP61xx buck family?
Yes, we hold spot stock as an independent distributor with quantities and date codes published on each product page. Request a quote for pricing.
Trademark & Disclaimer
MST, Feeling Technology and all part numbers are trademarks or registered trademarks of their respective owners. Jingteng Electronics is an independent distributor and is not affiliated with, endorsed by, or authorized by Feeling Technology. Brand names and part numbers on this page are used solely for identification and cross-reference. Electrical specifications must be confirmed against the original manufacturer datasheet before use. See our Legal Notice / Trademark Disclaimer.
Recommended next steps
If you are sourcing any of the parts mentioned in this guide, we can help you confirm stock, pricing, and lead times quickly.
- Upload your BOM — send your full parts list and receive a consolidated quote within 2 business hours.
- Browse related in-stock lines: Power Management ICs.
- Contact our team for hard-to-find or end-of-life components.
