Hi,
TL;DR: a precision linear MOSFET pre-driver capable of putting negative voltage on the gate in order to shut the current flow down. Quickly and hard to eliminate spurious noise-induced turn-ons.
Detailed:
I have a precision unbuffered 16-bit DAC that outputs 0--4.095V. The analog subsystem uses +12/-5V supplies in order to place the opamps (OPA4192) well within the linear region. Now I would like to buffer the VDAC voltage, but also augment the buffer with the ability to output some negative VNEG voltage in shutdown state. The closer VNEG is to the VEE rail the better, but the exact value is unimportant. I can see 3 possible scenarios based on a DG419 SPDT switch:
- Create a follower and add the mux to the input, switching between VDAC and VEE. But this can add noise/nonlinearities to the precision path.
- As above, but put the mux at the follower's output. This would add me ~30 Ohms to the output impedance.
- Connect the DAC directly to the +input of the opamp and put the switch between the output and the -input and VCC. In one position the mux would make the opamp act as a follower, in the other the inverting input's voltage would be much higher than the non-inverting one, so the open loop gain would make the output saturate somewhere close to VEE.
Other requirements and don't cares:
- the switching frequency between the DAC voltage (VDAC) and the negative output voltage (VNEG) is negligible (