Part Number: ADS1675
Other Parts Discussed in Thread: OPA211
Hi team,
In the ADS1675REF board reference Riso + DFB buffer circuit, the Riso(R25) is 100ohm, Rf(R22) is 49.9ohm, Cf(C22) is 0.15uF, this is very different from the design method of the precision labs video course (www.ti.com/.../ti-precision-labs-op-amps.html). In Precision labs series: Op amps - Stability - Isolation resistor : "RISO is selected to produce a zero in the AOL curve at the frequency where the AOL equals 20 dB. Then RF can be selected to any value greater than 100 times RISO in order to prevent interactions with RISO. The last step is to select a value of CF based on the range shown here. Using this range ensures that the two feedback paths never create a resonance that would cause instability."
The 100ohm Riso and 10uF capacitor load generate a zero point at only about 160Hz. I simulated this circuit, it has about 50 degree phase margin at about 7.5MHz, which is before the 0dB crossover.
So is this an optimal design that has been proven in reality? Will not has problems such as interference and resonance mentioned in the video course above.
Thanks,
Lee
