Simple Mosfet Driver for 3.3 logic

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1

Hey guys!

I am building an RP2040 based board which is going to operate car ABS solenoids.
That introduces two main challenges:

  1. Solenoids have very low impedance (some are as low, as 2ohms). So it is crucial to get the N-Channel Mosfet properly open. Most of logic-level ones still have pretty high resistance at 3.3 Vgs (like IRLB8721)

  2. Is, obviously, safety. So it would be wise to get Mosfets protected from Vgs overload. I know it could be done with two zeners, but there's two more components for each channel, and board is getting bit too big already

So, I wonder, if there could be a simple, compact (SOT-23?) Mosfet driver, which will rule out both things for me?

Thanks for your attention!

2

  • Assuming a 12V power supply, don't use a logic level MOSFET.

  • Add a fuse to the circuit (12V / 2R = 6Amp) a 10A fuse will probably be fine.

  • Add a kickback diode across the solenoid.

  • If the selected MOSFET, Vgs(max) is < 12V, add a voltage clamp zener to protect the gate.

BHBZ7

3

That was a super quick reply :slight_smile:

Pretty neat and simple solution, thank you!

Those are definitely must! I expect solenoids to kick real hard, hehe

Other than that- am I overthinking the whole gate protection thing, and flyback is the only precaution to really take?

I am integrating it into existing system, so fuses (on high side) are taken care of already :cowboy_hat_face:

4

  • MOSFETs have a maximum voltage the gate to source can withstand.

  • If Vgs is greater than Vgs(max), the gate can be damaged.

  • A zener can be placed across the gate to source to keep us from destroying the MOSFET.

  • In this HIGH Side Driver (P MOSFET) we see this zener.

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5

Yes, there are compact MOSFET drivers like the TM SOT-23 Single Low-Side Driver IC and IR44273LPBF. It features CMOS Schmitt-triggered inputs, under-voltage lockout, and is compatible with 3.3V logic. This driver can help ensure the MOSFET fully opens and provides some level of protection. Other recommended options include ZXGD3003E6Q, MCP14A0051T-E/CH and TPM27517-S5TR. They are also compatible with the 3.3 logic and have good temperature range.

3 Likes
6

Interesting. Would you provide a schematic showing one (or each, if you are feeling generous) of these drivers?

7

Each of the links opens a datasheet and all but one of those has an application circuit included in it - a few even on the first page.

8

Is one side of the solenoid connected to chassis ground?

9

You're the best! That's exactly what I was looking for. Many thanks!

One side is connected to 12v through the fuse and relay, and other- is pulled to the GND with N-Fets

10

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