I am amplifying the output of the NPP301-700A (differential pressure sensor) using the AD8237. The AD8237 is configured for a gain of 39.27 (G = 1 + (97.6k / 2.55k) ). Using my multimeter, I'm reading 0.012V at the NPP's differential outputs (Out+ vs Out-) when at sea level. This is expected. However, the AD8237 is outputting 1.1v when looking at Vout vs GND. At 39.27x, I should be getting ~0.471V, correct? I have included the Eagle schematic below.
Hi @gilshultz. Thank you for taking the time to review the schematic! Could you explain your thinking on not grounding REF? I was following the application note from AD for a single supply (datasheet page 23) and might have missed something?
Note looked at the data sheet but ....The picture shown is for a split rail supply , Gnd will be at 0v .
For a single rail supply the REF connection might need to be different.
This may be your problem , but look at the op amp dice too to see how close the output can get to the power supply rails , and in a high gain situation op amp offsets maybe significant .
@Hammy. Thanks for taking time time to review my schematic!
Note looked at the data sheet but ....The picture shown is for a split rail supply , Gnd will be at 0v .
For a single rail supply the REF connection might need to be different.
The ad8237 allows for single supply operation-- the picture I posted was confusing without context from the datasheet text. The caps on the "negative" rail are just omitted and this is connected to ground for single supply operation. Sorry about that!
This may be your problem , but look at the op amp dice too to see how close the output can get to the power supply rails , and in a high gain situation op amp offsets maybe significant .
I should be able to nearly hit rail to rail on this IC based on the AD web tools. At the current pressure input, I shouldn't be near a rail anyway. Does anything look out of the ordinary to you on the I/O plot (from the AD tools website) below?
