Other Parts Discussed in Thread: ADS124S08, OPA320, OPA350, OPA333
Dear Forum Members,
I'm writing to you regarding a design problem:
We'd like to use the ADS124S08 in one of our products (i.e. sensor signal conversion) and besides converting the analog output signal of a DMS sensor we want to use the internal voltage reference of the ADC as excitation voltage for the mentioned sensor. As the circuit would draw a larger current than the ADC can deliver, I thought about buffering the voltage using one of your operational amplifiers. I want to maintain the high precision of the internal reference, hence I chose the OPA625 because the description stated its use as a "Precision Voltage Reference Buffer".
When testing the OPA625, unfortunately I didn't get a satisfactory result. I'm assuming it's a design fault, that's why I need your help.
I use the 3.3V and ground from the ADS124S08 Evaluation Board as supply for the OpAmp, non-inverting unity gain (output -> negative input shortcut) and the ADC internal reference voltage from the EvalBoard as the positive input. The output voltage is not as precise as expected and depending on whether I use a load resistor or not, it varies significantly. What am I doing wrong? Or do you have any other suggestions on how to buffer the reference voltage precisely?
Thank you very much and best regards,
PS: Find the schematic and 3 photos (Measured Internal Voltage Reference, Measured OpAmp Output Voltage with and without load) in the attachment.Attached Photos.zip