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OPA2810: What do some kind of band width specs mention?

Part Number: OPA2810
Other Parts Discussed in Thread: OPA837,

Hi team, 

Could tell me the difference between SSBW and LSBW?

I understood SSBW = GBW/Gain, which shows input signal frequency capability for linear operation of OPAMP.

Could you tell me the meaning of LSBW and how to calculate it?

Regards,
Ochi

  • Hi Ochi,

    the large signal bandwidth is smaller than the small signal bandwidth because of the limited slew rate, which plays the dominant role at high amplitudes. To get the slew rate of a sine calculate the first derivative and you will get:

    U = A x sin (wt) -> dU/dt = A x w x cos (wt)

    where w = 2 x pi x f.

    So the slew rate is A x 2 x pi x f, which is 1V x 2 x pi x 38MHz = 240V/µs for a 2Vpp 38MHz sine. This is about what is specified in the datasheet:

    Kai

  • Well Kai, this is actually one of the more approximate spec mappings out there - one very simple error that has been pervasive (despite my 30yr effort to fix it) is that when you measure F-3dB on a LSBW sweep, your fundamental is actually -3dB down - right?? so your amplitude to go into this equation is 0.707*Vpp/2. Kind of sad that equation without the 0.707 factor keeps showing up in some of these datasheets - tells me the US profs never update their textbooks from legacy (sometime a bit off) material. Any of the 150+ datasheets I have done include that factor (1st came across that doing the CLC404 datasheet) - here for instance is one of the more recent - OPA837 - and here I included a 0.8 fudge factor that Xavier had come up with in one of his app notes 

    I have published quite a lot on this lately, but here is a review for the OPA2810 specifically which sadly appears to have a slower falling than rising SR - which complicates this even more, I did get a really good mapping for small signal from Aol to gain of 1 here though - I could go further with some large signal sims but not right now, 

    OPA2810 data sheet comments and model review.docx

  • Morning Ochi, Kai, et al, 

    At this point, I am sure this is way more than you had any interest in, but I went ahead and applied that transition region adjustment to the 2 LSBW numbers in the OPA2810 PDS 10V table. It actually does a really good job of mapping to a consistent 215V/usec SR from the 2Vpp and 4Vpp numbers. Then, even better, the model produces 215V/usec time ramp on a slewing edge - The approach in that article seems pretty effective, I would take other approaches as more approximate. The 24V table is a little higher, but not much, I did not analyze those. 

    Detailed LSBW to SR mapping.docx