I've got a bug in a project design with an opamp - the Microchip MCP6242 dual opamp to be exact. I'm missing something very fundamental about this chip and I'm hoping someone can set me straight.
I have a fluctuating voltage on the non-inverting input between 0 and 5 volts. For my testing, I'm supplying the voltages and can see the input voltages.
My first question is about the inverting input. I have a voltage divider with 15K resistors between Vdd (5V+) and Vss (Gnd). I should see 2.5V at the center which is connected to the inverting input. But instead I see 1.38V there. How is that possible?
My main question however is this: The output of the opamp is always the same at about .9 volts. I take the non-inverting input from rail to rail. The inverting input is stable at 1.38V. The output never budges. Can anyone tell me why?
Note, I have the output of the opamp feeding into an input of a pic chip. However, I have removed the pic chip, just in case I had a software goof in there somewhere. The results were nearly the same. Output voltage was a fractionally higher, but still unchanging.
I'm just trying to use this chip as a comparator. I want the output to go from 0 to 5 volts when the non-inverting input goes above the inverting input. Super simple application. But it's not changing.
Power and ground for the chip are present.
I have a fluctuating voltage on the non-inverting input between 0 and 5 volts. For my testing, I'm supplying the voltages and can see the input voltages.
My first question is about the inverting input. I have a voltage divider with 15K resistors between Vdd (5V+) and Vss (Gnd). I should see 2.5V at the center which is connected to the inverting input. But instead I see 1.38V there. How is that possible?
My main question however is this: The output of the opamp is always the same at about .9 volts. I take the non-inverting input from rail to rail. The inverting input is stable at 1.38V. The output never budges. Can anyone tell me why?
Note, I have the output of the opamp feeding into an input of a pic chip. However, I have removed the pic chip, just in case I had a software goof in there somewhere. The results were nearly the same. Output voltage was a fractionally higher, but still unchanging.
I'm just trying to use this chip as a comparator. I want the output to go from 0 to 5 volts when the non-inverting input goes above the inverting input. Super simple application. But it's not changing.
Power and ground for the chip are present.