I have a circuit powered from a single Li-ion cell. It contains a microcontroller which is powered by 3.0 V directly off the cell (through an LDO linear regulator).
This circuit has a 12 V load, so I designed a boost converter to step up the voltage from the battery, and to save on cost, rather than going with an SMPS controller IC, I've implemented the control logic in software inside the MCU, outputting the MOSFET switching signal from a GPIO with the same voltage level as the MCU's supply (i.e. 3.0 V) and limited current sink/source capability. Thus, a gate driver is called for.
Finding a suitable gate driver circuit has proved a daunting task, especially as most MOSFETs don't like being driven with only 3.0 V. My first attempt was to use the FAN3111 as a gate driver, but I didn't pay attention to its minimum supply voltage of 4.5 V. It was meant to be supplied from the boost converter's 12 V output, but this created a bootstrap problem: before I start switching the MOSFET, my boost converter's output is the battery voltage minus a diode drop, so not enough to power on the gate driver, and thus the switching won't start.
I investigated the following possibilities, but none are completely satisfactory, so I'm looking for new ideas:
Use a charge pump IC or even a small boost converter to generate the supply voltage for the gate driver. It feels like building a Rube Goldberg machine, plus after adding up the cost of the new supply IC (and supporting circuitry), the gate driver and MOSFET, it's cheaper to replace the whole contraption with an integrated switching regulator IC.
Use a complementary emitter follower-type gate driver IC, like this one. It's also cheaper than the FAN3111, but would require a level shifter from the MCU to the gate driver input, supplied by the boost converter's output. Initially the MOSFET would switch poorly due to the bootstrap problem, but after picking up some voltage it would work fine. This idea works in principle, but I've had no luck finding a suitable level shifter. Something like the CD4504 might work but it's a physically large IC at 16 pins and I can't afford the board space. There are other options but they start to get expensive. I also considered using a cheap BJT/MOSFET wired as a NOT gate, with a pull-up resistor from collector to the boost converter's output voltage. The problem is that, in order to save power, I'd have to go with a high value pull-up resistor, which prevents the MOSFET from being driven hard enough: the gate driver can only deliver 19 mA if fed from a 10 kΩ impedance, according to the datasheet.
Use the same complementary emitter follower-type gate driver IC as in (2), but drop the level shifting idea -- feed it directly from the MCU -- and go with a low Vgs(th) MOSFET. The choice of MOSFETs is more limited but this might work. However, according to the datasheet, the gate driver's output voltage could be as low as 2.2 V with 3.0 V applied, and as high as 0.5 V with 0.0 V applied. I'm especially worried that a low Vgs(th) MOSFET would be on the brink of conducting with 0.5 V applied. I'm not saying this can't absolutely work, but the lack of headroom feels troubling.
Can anyone point out alternatives that I'm missing?