negative voltage
Posted: Fri Jan 02, 2015 9:56 am
I have a need to drive a control line on an external piece of equipment. After some investigation, I now understand the control signal that I need to generate. There is one wire that needs these values (constant DC, until I want to change state) with respect to ground:
high - approximately +2.5 volts. This appears to be the default floating value, so if my output is high-Z with no voltage generated or sinking, I believe it would be acceptable.
zero - approximately ground, or sinking a few mA to pull the line low. The standard 'plug' that comes with the device shorts the input to ground to make this happen.
low - approximately -2.5 volts. This value was unknown, but discovered empirically. It was known that the device had a third state, and corresponding control value, but not documented. This is the value that I am trying to envision how to generate.
I have been looking at various 'charge pump' chips (e.g. Microchip TC7660), but I'm not sure how to get the 3-state output from them. I have also looked at a tech write-up at Digikey, on 'Generating Negative Output from Positive Input Voltage' using a synchronous buck regulator. I keep trying to visualize how to use these designs to get the 3-state output that I need. Could someone please nudge me in the correct direction to get to the proper design.
Whatever design I end up with, would need the 3 states controlled from a couple of output lines on a MCU.
TIA
high - approximately +2.5 volts. This appears to be the default floating value, so if my output is high-Z with no voltage generated or sinking, I believe it would be acceptable.
zero - approximately ground, or sinking a few mA to pull the line low. The standard 'plug' that comes with the device shorts the input to ground to make this happen.
low - approximately -2.5 volts. This value was unknown, but discovered empirically. It was known that the device had a third state, and corresponding control value, but not documented. This is the value that I am trying to envision how to generate.
I have been looking at various 'charge pump' chips (e.g. Microchip TC7660), but I'm not sure how to get the 3-state output from them. I have also looked at a tech write-up at Digikey, on 'Generating Negative Output from Positive Input Voltage' using a synchronous buck regulator. I keep trying to visualize how to use these designs to get the 3-state output that I need. Could someone please nudge me in the correct direction to get to the proper design.
Whatever design I end up with, would need the 3 states controlled from a couple of output lines on a MCU.
TIA