So, I have a power headache :)
One of the chips I want to use in a project has very specific power require ments ...
- The VDD supply must ramp from 0V to its final value within 10ms to ensur e correct startup. - The IO VDD supply must ramp to its final value before VDD reaches 0.4 V. - The power supplies must be brought up monotonically - (other stuff that's not so relevant)
... and at the same time, I need a fair amount of power (in this case about 5A on the 3.3v supply and about 2A on the 1V supply to cover the worst-cas e scenarios). As far as I'm aware, there isn't a single chip solution that can handle this, so I'm trying to figure out how to guarantee all the above .
One way I came up with was to sample the 3.3v and 1v lines via an AVR chip' s built-in ADC's. There's already an AVR on-board so it doesn't need any mo re components, just a bit of wiring. Once the voltages have stabilised to t heir correct final values, I would just have the AVR allow the supply of vo ltage to the rest of the board.
The question is how to do that ? I thought of using solid-state relays, but looking at the ones at digikey that can handle the power, the variance in on-time switching is such that I'm not sure the monotonicity (which I'm int erpreting to mean 'at the same time') would be preserved.
So, a vague thought about MOSFETs surfaced - thing is I've never used them, hence this long plea for help :) A few questions:
- Can I just connect the source to v-reg output, drain to the rest-of-the- world, and gate to the AVR to switch 5A ?
- Does a MOSFET care about the voltage it's switching ? In other words, wi ll it work if Vds = 1v ? In the datasheets, I only see maxima specified, so I'm assuming there is no minimum value but it's worth asking :)
- Any recommendations on which one to use ?
- Is there a better way to do this that I'm missing ? :)