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I am interested in designing a BLDC motor driver capable of operating at low supply voltages and relatively high currents (i.e. a device capable of operating with a 3V minimum supply and a phase current > 4A would be ideal). My preference is to use only N-channel MOSFET's, for the usual reasons they're preferred for BLDC motor drivers. To achieve this, I have been investigating half bridge pre-driver IC's. After an exhaustive search (on digikey), I was unable to find any half bridge gate drivers (i.e. both high and low side N-MOS) capable of operating below ~5V (the lowest I've found is the DGD05473, which can operate at 4.5V with an external bootstrap diode).

I am wondering if there is some fundamental reason why these gate drivers have a 5V minimum that I'm missing? Out of thousands of options I expected to see at least a few which could operate at a low supply voltage. If so, does this essentially relegate me to using P-MOS to switch on the high side, or would it be feasible to build out my own discrete high side N-MOS gate drive circuit (inexpensively and in a small form factor).

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    \$\begingroup\$ If you want a H-bridge purely using NMOS fets you must have a voltage higher then your supply voltage, no matter if the supply is 3V or 300V. That is why many (all??) CMOS H-bridges driver ICs have a voltage boost circuit. \$\endgroup\$
    – Oldfart
    Mar 12 '20 at 19:17
  • \$\begingroup\$ Yep, I know this. I usually see this implemented with 'bootstrapping' or a charge pump. But I don't see the connection between this requirement and the (apparent) 5V minimum voltage for these kinds of devices. \$\endgroup\$
    – Ocanath
    Mar 12 '20 at 19:21
  • \$\begingroup\$ So why are you then talking about using a P-MOS to switch? The solution I would think of is to build a 3V boost circuit. Also beware that very few FETs can work with 3V at the gate. \$\endgroup\$
    – Oldfart
    Mar 12 '20 at 19:23
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    \$\begingroup\$ Because it's a vanishingly small market. Until you make it a big market, just use a low power boost converter to power the drive circuitry. \$\endgroup\$ Mar 12 '20 at 19:24
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    \$\begingroup\$ Ah, unless you mean that I should use a boost converter to power one of these existing gate driver chips. I've considered this, but am still curious about the underlying reason behind the apparent 5V limit. \$\endgroup\$
    – Ocanath
    Mar 12 '20 at 19:59
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Apparently, I just didn't look hard enough. I couldn't find any half bridge drivers that operate below 4.5V, but there are high side integrated gate drivers that do (such as the MIC5018).

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    \$\begingroup\$ The half-bridge drivers that operate below 10V are rarer but they are more common than they were 10 years ago. At such low voltages, and presumably powers, the system is presumably aiming for simplicity and the Vgs of a PMOS is far from being exceed so I would just go PMOS and pull the gate straight to ground rather than using high side NMOS. \$\endgroup\$
    – DKNguyen
    Mar 25 '20 at 17:50

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