AFE range switching design review request

[Bootalito]

I'm designing a 200W 30A 150V Electronic DC load.  Below is my voltage input AFE design.

It has two ranges a 0-150V and a 0-15V range simply switching in a different "taps" on a divider network. 
Can I get people to critique please.

[max_torque]

hmm, not sure about that way to be honest!

Your fets need to be driven with a high side driver because they float on the input to the ADC, and you have no series R between your input protection (BAT54 (leaky!) and Zeners) and the ADC input, so all that will happen is the internal diodes in the ADC will do the clamping


I'd have a fixed 50:1 input divider with precision resistors, buffered by an op amp, with two gain settings 1:1 and 10:1, feed that into the ADC input, through a suitable AAF (depending on your sample rate and bandwidth requirements)

[max_torque]

I'd also add that anything you might connect to a 150v input is (highly) likely to contain more than 150v and hence you should design (creepage/clearance/component ratings) you input to safety survive far more than that (300v wouldn't be un-typical)

[Bootalito]

hmm, not sure about that way to be honest!

Your fets need to be driven with a high side driver because they float on the input to the ADC, and you have no series R between your input protection (BAT54 (leaky!) and Zeners) and the ADC input, so all that will happen is the internal diodes in the ADC will do the clamping


I'd have a fixed 50:1 input divider with precision resistors, buffered by an op amp, with two gain settings 1:1 and 10:1, feed that into the ADC input, through a suitable AAF (depending on your sample rate and bandwidth requirements)

Duh..of course.  There Vgs would be...nothing...anything...wouldn't work.  By high side are you talking about a pchannel mosfet?  How would I drive that to not exceed Vgs?

As far as the op amp buffer what do you think of a diff op amp configuration in unity gain:

I'd also add that anything you might connect to a 150v input is (highly) likely to contain more than 150v and hence you should design (creepage/clearance/component ratings) you input to safety survive far more than that (300v wouldn't be un-typical)

I've been moving things around on my PCB a bit just to see where things fit and have been consulting www.CREEPAGE.com.  I'm maintaining 3.5mm to 4.5mm creepage between parts that will regularly see this much deltaV.  I've cut around the center pin of the mosfets I'm using as well: