Plan is for the ATtiny to actually mostly be asleep on the battery voltage. The 5V driver IC has an enable pin and goes into bypass mode when it's not enabled. Only when it wakes up will it turn on the 5V.
I want the 5V for the 4.5V gates on my MOSFETs, the OLED display (IIRC, it will also run on 3.3V), and the 20mhz for PWM and ADC.
DC/DC convertor. I'm hoping I can make a synchronus inverting buckboost supply in the neighborhood of 25w/6V max.
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.