LM25118 Auto Buck-Boost Non-Synchronous DCDC Power Module, 4.5–35 V input, 1.23–31 V adjustable output, up to 8 A output current, peak efficiency 92 %, switching frequency 400 kHz.
LM25118 is a 3–42 V wide-input, current-mode, non-synchronous buck-boost controller.
For a university power-electronics training assignment we had to build a power module (5 V input, 1.8–24 V output, 2 A max), so I made this LM25118 board—non-synchronous Buck-Boost topology.
In the actual circuit I swapped the MOSFET to NCE6050KA: with 5 V input the LM25118 gate-drive PWM is only 3.8 V, while the original NCE7560K needs 4 V to fully turn on, so it was running in the linear region and the output was wrong. NCE6050KA fully turns on at 3 V.
I also changed the inductor to 6.8 µH. On the prototype the LM25118 pin 2 (UVLO) wasn’t routed in the schematic, so I had to add a fly-wire; both the PCB and schematic below are already fixed.
If you need higher input/output voltages, just substitute higher-voltage-rated filter capacitors and adjust feedback resistors R9 & R10—formulas are in the datasheet.
Schematic and PCB files are at the end of the article, or view them on the LCSC open-source platform.
LCSC open-source link: https://url.zeruns.com/nAPDy
LM25118 datasheet: https://url.zeruns.com/j2PjZ
- SY8205 Synchronous Buck Adjustable DCDC Module (schematic & PCB): https://blog.zeruns.com/archives/717.html
- 2011 National Electric-Cup Topic: Parallel Switching-Power-Module Supply System: https://blog.zeruns.com/archives/718.html
Photos
LM25118 Brief
The LM25118 wide-voltage buck-boost switching regulator controller contains all functions needed for a high-performance, cost-effective buck-boost supply using minimal external parts. The buck-boost topology keeps the output regulated whether the input is below or above the output, making it ideal for automotive applications. When the input is sufficiently higher than the regulated output the device runs in buck mode, then gradually transitions to buck-boost mode as input approaches output. This dual-mode approach maintains regulation over a wide input range, gives best buck-mode efficiency, and provides glitch-free mode changes. The controller includes drivers for both high-side buck and low-side boost MOSFETs. Control is based on current-mode with emulated current ramp, reducing noise sensitivity and allowing reliable control of the very small duty cycles needed at high input voltages. Protection features include current limit, thermal shutdown, and enable input. It comes in a thermally enhanced 20-pin HTSSOP package with an exposed pad.
Component Purchase Links
- 0805 resistor sample book: https://u.jd.com/DzK9k0O
- 0805 capacitor sample book: https://s.click.taobao.com/cTZzzDu
- LM25118 IC: https://s.click.taobao.com/4FauRDu
- NCE6050KA: https://s.click.taobao.com/YgFKpDu
- SBDD2045CT: https://s.click.taobao.com/Le4KpDu
- KF7.62 terminal block: https://s.click.taobao.com/txVJpDu
Recommended supplier: LCSC. Discount registration link: https://activity.szlcsc.com/invite/D03E5B9CEAAE70A4.html
All board parts are available at LCSC; in the open-source project BOM click “Add All to LCSC Cart” to import everything instantly.
Test Data
Load Regulation
12 V input, 31 V output, no-load current 0.019 A, no-load power 0.22 W.
| Input V | Input A | Input W | Output V | Output A | Output W | Eff. |
|---|---|---|---|---|---|---|
| 15.01 | 4.56 | 68.45 | 12.06 | 5 | 60.3 | 88 % |
| 6.51 | 5.15 | 33.53 | 12.11 | 2 | 24.22 | 72.2 % |
| 6.01 | 3.95 | 23.74 | 1.81 | 8 | 14.48 | 61 % |
| 6.51 | 3.86 | 25.14 | 1.99 | 8 | 15.91 | 63.3 % |
| 7.01 | 4.32 | 30.28 | 23.89 | 1 | 23.89 | 78.9 % |
| 11.99 | 2.19 | 26.26 | 23.13 | 1 | 23.13 | 88.1 % |
| 24.01 | 1.62 | 38.9 | 12.03 | 3 | 36.09 | 92.8 % |
| 24.01 | 2.72 | 65.31 | 12.03 | 5 | 60.15 | 92.1 % |
| 12 | 4.35 | 52.2 | 30.38 | 1.5 | 45.57 | 87.3 % |
| 7.99 | 5.05 | 40.35 | 12.05 | 2.5 | 30.13 | 74.7 % |
Ripple Tests
12 V input, 5 V output, no load: ripple ≈ 8 mV pk-pk.
12 V input, 5 V @ 2 A: ripple ≈ 15 mV pk-pk.
6 V input, 12 V @ 1.5 A: ripple ≈ 230 mV pk-pk.
12 V input, 23 V @ 1 A: ripple ≈ 300 mV pk-pk.
12 V input, 24 V output, no load: ripple ≈ 34 mV pk-pk.
12 V @ 2 A output (input forgotten): ripple ≈ 25 mV pk-pk.
Schematic
PCB
Top layer:
Bottom layer:
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- 2007 Electric-Cup power topic: 30–36 V adjustable boost DCDC (UC3843): https://oshwhub.com/zeruns/36v-sheng-ya-dcdc-mo-kuai-uc3842
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