OPA2830: Very basic question about the usage of "beffer" amp

Hi ,

Is this the phase margin information you want? Or you can use spice simulation to verification your circuit.

Figure 39. OPEN-LOOP GAIN AND PHASE

OPA2830 TINA-TI Spice Model 

OPA2830 TINA-TI Reference Design (Rev. A)

I have no idea about the noise you encountered. Hope someone else can help you.

Thanks!

This is not the phase margin plot, this is the open loop gain and phase plot. Would need the load for phase margin simulation, 

Also, your series 10ohm is good idea for these parts - or zero ohm source often will look inductive giving a local oscillation in the input transistor - macromodels will not show that issue. 

Hi Takumi,

very probably you have probed the output of OPA2830 with the scope without inserting an isolation resistor. This can be problematic because of the scope probe capacitance. See figures 37 and 38 of datasheet. Also see the section "Driving Capacitice Loads".

Kai

Hello Suzuki-san, 

   Also, I want to add this blog post that could be helpful here, it discusses probable instability on buffers with feedback resistors. However, as Michael mentioned, a small resistor in the feedback of a buffer is a good idea. Figure 5 in the blog post shows phase margin as feedback resistor increases. And, below I have attached stability circuit setup/simulation of the OPA2830 following your specified condition which is showing around 59 degrees of phase margin.

OPA2830_Stability.tsc

Thank you,

Sima