0
\$\begingroup\$

I want to create a 0.8V reference derived from 5V using voltage divider and buffered using OPAmp.

This is my schematic enter image description here

I will be using this voltage reference for signals upto 10 Mhz (in peak detectors).

Do I need to worry about the Unity Gain bandwidth of Op AMP used as buffer?

Thanks,

\$\endgroup\$
  • \$\begingroup\$ Do you wish to be able to capacitively load your buffered reference, at present you won't be able to put bypass caps on the output. Zo will be modest at 10 MHz this way too \$\endgroup\$ – sstobbe May 17 '17 at 23:14
  • \$\begingroup\$ yes, I may need to put decoupling caps. What should be done in that case? \$\endgroup\$ – Ash May 18 '17 at 0:18
  • \$\begingroup\$ The way I typically go is ti.com/lit/ug/tidu032c/tidu032c.pdf on fig 17, but there are many ways to accomplish this \$\endgroup\$ – sstobbe May 18 '17 at 0:49
1
\$\begingroup\$

The LTC6200 impedance at 10MHz is 100x higher than your C11=0.1uF

Also it adds overshoot with even light capacitance load.

If your transient loads are significant then OK add a series RC after the unity gain OP Amp but as I would expect , you wont have significant load current so the R ratio is adequate to feed many comparators.

enter image description here

conclusion:

get rid of Op Amp.

Also, what is the tolerance on your need for 0.8V because the tolerance on your Vcc will drive the error on this. 2%?? 5%??

Generally if you need a good reference we use LDO's or bandgap zeners but if your Vcc is stable within 0.8V tolerance spec, just the R ratio is fine.

RC= 6k//0.1uF results in a few hundred Hz LPF whether you have an Op Amp or not but at least no overshoot on turn on. (which may not matter)

\$\endgroup\$
4
\$\begingroup\$

The LT6200, per the data sheet is unity gain stable, so it will work "just fine". I use quotes for 2 reasons. First, with a gain bandwidth product of 165 MHz it is much faster than necessary, and as the saying goes, "Those who ask for more bandwidth than they need deserve what they get." In this case the penalty is that the follower will be more prone to oscillation than a slower op amp, and you'll need to be careful about layout and decoupling. Second, your voltage accuracy will be entirely dependent on the stability of your 5 volt supply, which is not normally a good approach to take.

\$\endgroup\$
  • \$\begingroup\$ what you will suggest to improve the accuracy of reference? \$\endgroup\$ – Ash May 18 '17 at 0:20
  • \$\begingroup\$ I'd suggest you consider a TI TL431 if your accuracy needs are moderate (cheap replacement for any zener). If you need < mV variation on your peak detector, you could consider any of the voltage references available. \$\endgroup\$ – Jack Creasey May 18 '17 at 5:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.