I'm tinkering with the ATtiny 2 series (ATtiny 3224). I'm also starting to teach myself about switch mode power and surface mount design. I'm planning to drive two Toshiba SSM6K804R MOSFETs. They are logic level MOSFETs with a 4.5V drive. They have a gate capacitance of 1110pF (1nF).
Even though these are logic level MOSFETs, I think I still need an external gate drive for them for crisp switching above a few kHz. I don't need to try and charge the gate directly with the ATtiny as I would need a 2-300ohm resistor in series to protect the microcontroller and that will slow everything down. Also need a pulldown for the gate.
Can someone please recommend a simple IC or maybe a packaged transistor pair that I can slam the gates with?
Questions/comments/advice greatly appreciated!!
After a little more thinking about the problem you're trying to solve, an op-amp voltage buffer with an off the shelf DC-DC converter for the high voltage rail might be the simplest overall circuit. Unfortunately the ATtiny you're using doesn't have a digital to analog (DAC) output, so it's hard to set the voltage reference with that setup. You could probably rig up something with a PWM channel and a capacitor on the output, and adjust the gain on the op-amp feedback so you can reach the max output voltage you want (6V ?)
Unless of course the goal is actually to learn how to build your own variable output buck-boost converter, in which case, all the power to you!
Edit: I just realized 25W/6V means you'd be delivering over 4 amps... Those would not be very cheap op-amps. Have you measured the actual load you're driving? This could end up very similar to a 25w class D audio amplifier circuit depending on your load impedance.
I'm looking at the FAN3224, a gate driver capable of several amps at 5V to run my MOSFETs. I'll probably play with direct driving them with the ATtiny at first just to familliarize myself.
The original circuit is running some sort of bridge configuration. I've used a 1.6ohm load for years, with wattage set to 14.5 or 14.8. However, the orignal is capable 25w in the lowest output version. I'm not sure what resistance range it's capable of pushing that 25w.
And, yes, the goal is to build a variable DC supply. I'm finding it really interesting. I'm looking at the synchronus inverting buckboost. I think my final version would use half the components of the original.
If I understand this stuff correctly, (real big if), with the convertor pushing negative voltage, I sidestep high side drive problems. My load is dumb resistance so it doesn't matter how noisy or negative its power is.
So the ATtiny has an ADC capabale of running in windowed mode. A lot of the peripherals are able to run independently of the CPU, you can link them up with onboard programable logic called CLC. So, using logic I can tie the ADC to my PWM at pretty fast speeds. It also has a selection of internal voltage references. I'm planning to use some sort of voltage divider for feedback to the ADC, using the logic to vary my duty cycle when the voltage goes out of bounds.
Before I get that far out in the weeds, I need to play with mosfets, pwm, an inductor, and my new scope.