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I've been searching for a very-small package op-amp and not having much luck. LTxxxxxx (edited out) would be ideal however the slew rate is just too low. Is there a way of controlling/increasing slew rate using external components?

The op-amp is used to be used as a voltage follower for 10kHz signal.

Edit: I have intentionally given little information with regards to what I am after as I have looked up many different devices that meet my specification in slightly larger packages. While doing this search I got side tracked with the possibility of increasing slew rates, but could not find much information so I posed the question here. Sorry for any confusion.

Clarification:

I am not asking for suggestions of higher slew rate op-amps. I was not thinking the particular op-amp I referenced should be higher slew rate. I edited out the component name because a fellow SE'r suggested specific components may not be allowed (hence LTxxxx)

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    \$\begingroup\$ Buying suggestions are not allowed on this website. Try harder, mate. \$\endgroup\$
    – ammar.cma
    Commented Jul 17, 2017 at 11:15
  • \$\begingroup\$ I am not asking for a buying suggestion... I am asking if there is a way of controlling/increasing slew rate of op-amps. \$\endgroup\$
    – R.Joshi
    Commented Jul 17, 2017 at 11:21
  • \$\begingroup\$ What kind of slew rate do you need? You need to buffer a 10k signal. I think lot of opamps can do that now. \$\endgroup\$
    – ammar.cma
    Commented Jul 17, 2017 at 11:23
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    \$\begingroup\$ Use LTyyyyyy (edited out) instead, it has a higher slew rate. \$\endgroup\$
    – user16324
    Commented Jul 17, 2017 at 11:59
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    \$\begingroup\$ Why do you need a tiny package if you have room to add external components? You need to be a LOT clearer about what your requirements and your constraints are before we can give you any meaningful guidance. Deliberately withholding information is not helping your case. \$\endgroup\$
    – Dave Tweed
    Commented Jul 17, 2017 at 12:18

3 Answers 3

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Is there a way of controlling/increasing slew rate using external components?

For a given op-amp and without adding complex circuits that make it unfeasible as a solution, there is no clever or subtle way of increasing the slew rate of a regular (or less regular) op-amp.

Clearly there will be a limited number of exceptions but these are likely to be specialist devices that probably won't be available in a low package size.

Possibly what might be a good choice for low voltage supplies is the OPA333 but you have given very little to go on so it's at best a guess that might point you towards a better solution. You can get it in a 2.1 mm x 2.0 mm package.

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  • \$\begingroup\$ oh okay that makes sense to me. To decrease slew rate or apparent slew rate a low pass filter could be used? but there is not a similar method for increasing it. Thank you for the reply. \$\endgroup\$
    – R.Joshi
    Commented Jul 17, 2017 at 11:47
  • \$\begingroup\$ Thanks for the suggestion. I really appreciate it. However I am limited to a very small number of devices that can be used. \$\endgroup\$
    – R.Joshi
    Commented Jul 17, 2017 at 11:54
  • \$\begingroup\$ Op-amp suppliers have to compete in a dog-eat-dog market and they will produce devices with the fastest slew rate possible whilst maintaining op-amp stability (a big issue) so, if there was a way of increasing the slew rate, this would be implemented inside the device in order to attract a bigger market share. \$\endgroup\$
    – Andy aka
    Commented Jul 17, 2017 at 11:57
  • \$\begingroup\$ It's just a suggestion and a stab in the dark. This answer is about explaining why slew rate increases are not feasible. \$\endgroup\$
    – Andy aka
    Commented Jul 17, 2017 at 11:58
  • \$\begingroup\$ Any reason for the down vote anyone? \$\endgroup\$
    – Andy aka
    Commented Jul 17, 2017 at 13:47
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Op Amp slew rate is determined internally, using a controlled current to charge a total capacitance composed of parasitic and lumped onchip capacitors.

Over temperature and VDD, you will have some variation in that charging current, and some variation in parasitic and lumped capacitance.

Also, as the IC process varies (implanting, annealing temperature, etc), current and capacitance will vary; the designer likely will use circuit aspects that correlate current and capacitance ....... to compensate for variations, and hold the SlewRate approximately constant.

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  • \$\begingroup\$ Correct me if I am wrong. So what you are saying is that there is a way maintaining a specific slew rate but not changing it? Do you have any specific examples? \$\endgroup\$
    – R.Joshi
    Commented Jul 17, 2017 at 13:29
  • \$\begingroup\$ I've assisted people who designed op amps on silicon. I recall the words "PTAT" and "CTAT", where P is proportional, and C is complementary. \$\endgroup\$
    – analogsystemsrf
    Commented Jul 17, 2017 at 14:49
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Similar boat, Bro'. If you amplify x2, from 1Vp-p to 2v p-p, you have increased slew-rate ( for a SINE wave). The problem is what happens when that 2V- p-p signal hits the 1V p-p envelope of the original signal. And once you start to clip, what happens to those dozens of happy overtones you are about to destroy? The 2nd derivative tells you the rate-of-change of the slew rate. So if your source is digital, all those leading-edge wizards have the answer ( Bessel, Betterworth, Sallen-Key, Chebyshev). But if your source is analog, searching "Analog frequency multiplier" will prove the lack of interest on the topic. Consider 2-stages of differentiators, and see how they do through an error amplifier ( Note, NOT "2nd ORDER" differentiator).. Cheers

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