LMH6643: Slew rate

Sure,

First the -3dB BW is usually considered a small signal effect that follows a 2nd order response shape. THe starting point is the gain bandwidth product idea where the -3dB is determined by dividing the noise gain into the gain bandwidth product - that only applies for a single pole loop gain and there is always a lot of -3dB BW extension in higher speed parts as the phase margin decreases until it hits a 1.6X multiplier over the crossover frequency for phase margin <65deg.

That is actually kind of a new result that I put into the much more detailed description of this analysis into this article, the curves are all here to relate loop gain phase margin to closed loop small signal shape,

www.planetanalog.com/author.asp

Then tying that to large signal is a another big step. For step responses with ideal input steps, the output tries to follow the input with a 2nd order shape that will have a peak dV/dT based on the Fo and Q. You can solve all of that and estimate the peak slew rate on a step is approximately 2.85*Vstep*F-3dB (for 0.7<=Q<=1.5) and if the numbers don't exceed the available slew rate, it will not slew limit. Then to try and tie that to a LSBW is always a bit approximate. The equation you showed is kind of classic but not that accurate for slew enhanced devices. Also you need to use the Vpeak on a sinusoidal waveform, not the Vpp. But in any case various adjustments to this equation have been made. I tried to step through all of these issues in a 2 part article here - in the 2nd part I actually decided I could get better match from slew rate to FPBW if I RMS's a linear SSBW with a slew limited LSBW - more than you probably wanted, but if you had your exact requirements - pretty easy for me to screeen down to suitable (but not too much over performance) choices. The input you showed above is I guess 10MHz, 0 -2V, what is the output? Any gain, is this a step or a sinusoidal waveform? The LMH6643 you mention is an older dual RRO VFA with very high noise - if a 5V total supply is ok, look at the OPA2837. If you need +/-5V look at the OPA2890.

www.edn.com/.../What-is-op-amp-slew-rate-in-a-slew-enhanced-world--Part-1

www.edn.com/.../What-is-op-amp-slew-rate-in-a-slew-enhanced-world--Part-2

Hello;

signal is sinusoidal.
Gain is 1.(unity gain).

Best Regards.

Hello;

Firstly thank you for your reply.

Yes, I am doing a buffer.


Best Regards.