Comment on Driving a logic level MOSFET with an ATtiny 3224
litchralee@sh.itjust.works 2 days ago
A push-pull BJT configuration seems like it could be appropriate, if your application will be unbothered by limiting the Vgs to a max of 5.5v (the 3224’s max supply voltage). The MOSFET in question seems to be good for Rds(on) below 20 mOhm at that voltage, so it seems fine for at least a handful of amps.
If you are doing higher frequency switching than a few kHz, then you probably want to use a driver IC. And especially so if you have a higher voltage bus than the 5v needed by the ATTiny.
I’ll be reading up on push-pull. Thank you!
Main power source is a single cell lithium, so 3.7ish volts. Supply for the ATtiny is a 5V driver IC (I’ve already got it working).
The convertor I want to build will be inverting as the load is basically a pure constant resistance. (14.5w 1.6 ohm typical). I think that means I sidestep all the problems with a voltage higher than my control.
I’m hoping to use the window mode of the ADC and the programmable logic (CLC) to actually control the convertor mostly independent of the CPU.
litchralee@sh.itjust.works 2 days ago
I suppose it’s worth mentioning that the 3224 datasheet suggests that it’s perfectly capable of running at 3.7 volts directly, since it has a wide voltage range from 1.8v to 5.5v absolute. But I imagine you have other ICs that need the 5v supply.
I’m not entirely familiar with what you mean by a “convertor”, but I presume it’s some sort DC to AC function. Given the output loading, 3 amps through that Toshiba MOSFET seems reasonable enough, with the power dissipation being something like 0.3-0.5 W max, depending on switching speed.
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.
xthexder@l.sw0.com 1 day ago
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!