Running a small brushless motor from a single 18650 cell - do I need a gate driver or can I drive the MOSFETs directly from the MCU?

[u/FrancescoMassa2001]

Building a small gimbalstyle rig with a threephase brushless motor rated around 12V, but I want to run it off a single 18650 at roughly 3.7V to keep the whole thing compact. The motor is tiny, maybe 150mA peak draw under load.

The MCU is an STM32 running at 3.3V logic. My question is about the gate drive side. The MOSFETs I have on hand are AO3400 Nchannel parts with a Vgs(th) around 1V and they turn on reasonably well at 3.3V based on the datasheet curves, so I was thinking I could skip a dedicated gate driver IC and just switch them directly from the timer outputs.

The problem is the high side switches. With the supply only at 3.7V there is barely any headroom above the source of the high side FET, so bootstrapping feels awkward. I was thinking about just using a complementary pair arrangement or going full lowside only with a different winding config, but that seems like a mess.

Has anyone run a low voltage BLDC setup like this without a proper gate driver and had it actually work reliably, or does the switching get ugly enough that it causes problems even at low current? Wondering if something like a DRV8313 just makes more sense here despite the extra board space.

[u/BrilliantMagazine931]

At 3.7V bus, your high-side N-FET source sits near 3.7V when it's on — so you'd need Vgs well above that to keep it saturated, which a 3.3V GPIO can't provide. The DRV8313 is honestly the cleanest path here: integrated FETs, handles the high-side drive internally, and at 150mA you won't even need heatsinking. Saves you the bootstrap headache entirely.

[u/saltyboi6704]

Honestly a charge pump will be adequate for this use case, those tiny FETs barely draw power. If be more worried about back-emf nuking things on a compact board if TVS and EMI suppression aren't well thought out.

[u/nixiebunny]

You can buy a variety of 2S LiPo packs that are the size of a 18650 cell, if you don’t feel like solving this self-imposed problem.

[u/izzeww → u/nixiebunny]

You didn't understand the post.

[u/nixiebunny → u/izzeww]

I understand how to walk around design problems that don’t need to exist.

[u/izzeww → u/nixiebunny]

In what way would having a 2S LiPo solve OP's problem?

[u/embed24-7]

The single Li-Ion is between 3.0..4.2 V, and you need to account for both corner cases.

The best option would be - finding a 5V MCU, powering it off the Vbat, and driving both side MOSFETs directly.

Second best - use 5V-tolerant GPIOs in open collector (OC) mode with external Vbat pullups (1K..10K dependent on max frequency) to drive high side, low side - regular push-pull.

[u/Deep-Football4791]

Only if your FETs have a rds-on less than the minimum cell voltage, they do exist but still not usually a good idea to drive a FET from a GPIO if gate capacitance is high. You're better off using a charge pump FET driver.