I have two problems to solve and hopefully this can be done with a single (dual) part.
1. Supply a "clean" -15 V at about 35ma to a transimpedance amplifier from a -38V source,
2. Provide a steady-state -38V and (2) a timed sweep from 0V to around -5V. Here, nanoamperes of current are involved.
I considered an LDO for -15, but those I can find won't take the -38V presently coming from a converter and we don't want to create another noisy switching converter!
So I'm thinking a "high output current" amplifier (dual package) powered by our available -38V (with the + rail of the amplifier to system ground) would be an option. One of these would produce the -15V based on bias at the inverting input, and the other driving the -38V rail with a mosfet-selected triangle generator for the timed sweep.
Does Analog Devices have a suitable part for this idea.. or other ideas that will give us these voltages?
ADA4700-1 is not a rail-to-rail output opamp, i.e. output swing is limited to 1-1.5V from either rail. If you need to drive 0V, then the Vs+ needs to be +1.5V or higher. Pay attention to the capacitance of the load (static plate) to maintain stability.