Other Parts Discussed in Thread: REF5010, REF5050, OPA2209, OPA4209
Hi,
I'm currently looking at implemented something similar to the the TIDA-01427 for one of our ultrasound AFE designs. However we have a +/-12V supply available on our board rather than the +/-15V in the reference design. Once factoring in LDOs to clean up the supply rails, that probably gives us +/-11V supply.
Looking at the OPA2209 (well actually OPA4209 given part availability), it looks like the maximum input common-mode voltage will be around +/-9.5V. As such we will need to either reduce the reference output voltage of the REF5010 or find a lower output voltage precision reference. After a bit of searching the next lower voltage reference I can find is only 5V (e.g. REF5050) which is a bit low. Really we need somehting around 8-9V.
I see a couple of ways of reducing the reference voltage into range, and would like some advice as to which is likely to be the better option:
1. The REF5010 has a "TRIM" pin which allows adjusting the voltage. How accurate are the reported resistor values for the TRIM pin? For example if I were to place an 88.7kOhm 0.05% resistor from the TRIM pin to ground, this should in theory reduce the voltage down to 9V.
2. Alternatively, the design uses two channels of the OPA2209 to buffer the output voltage. I could leverage these two buffers to attenuate the voltage of the reference. For example I could change R24/R25 to a 1.8k resistor, R17 to a 1.62k resistor, and adding an additional 16.2k resistor from the U5A +ve input to GND, as shown below. Using say 0.5% or even 0.05% tolerance resistors should maintain a reasonable degree of accuracy, given the later attenuator is specced at 1% tolerance resistors.
Alternatively, can you recommend an alternate Op-Amp or voltage reference for generating a +/-9V reference for the DAC?