Op Amp Voltage Ranges—input and output, clearing some confusion

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Alex Scott — Fri, 20 Aug 2021 12:22:25 GMT

This is really true that some op amps claim only a rail-to-rail output, lacking the input characteristics shown in figure 3. Rail-to-rail op tree chipper amps are very commonly used on single 5V supplies and lower because they maximize signal voltage capability on their limited supply range.

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Doug Smyth — Mon, 11 Mar 2019 14:23:25 GMT

Very good explanation Bruce. Adding this link to all op-amp application notes would be beneficial to many.

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Otavio Augusto Gomes — Sat, 01 Apr 2017 20:52:55 GMT

Clearly explained Bruce. Perhaps the best. Thanks.

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

om prakash1 — Sat, 07 Nov 2015 03:57:41 GMT

Hi Brush, Very clearly explained in this blog what is rail to rail means. Very much thanks for explanation.

I was making a collection of Op Amp of TI as well as other manufacturers for Rail to Rail 'Negative Input only' and 'Positive Input only'. I found TI describes only for OPA835, OPA836 and THS4521-HT as 'Negative Rail Input' devices. There are many other Op Amp like TLE4121, LM611 where common mode input voltage goes upto ground or below the negative rail (for LM611 Common-Mode Range: V− to (V+−1.8V)), My confusion is if the input reaches to negative rail or below these should be grouped as 'Negative Rail In' devices. Like wise when C-M input goes to positive rail or slighltly above, all those device should be understood as 'Positive Rail In' devices. But I do not see if TI describes anywhere as 'Positive Rail In' in the description. I shall be very thankful if you can spare some time for me.

Thanks in advance.

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

harish jangid — Fri, 11 Jul 2014 11:07:48 GMT

Thanks Bruce..

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Bruce Trump — Thu, 10 Jul 2014 20:57:21 GMT

Harish— The linear input voltage range of an instrumentation amplifier is quite different from an op amp. The combination of differential and common-mode voltage can overload internal node voltages in ways that are not so obvious. The typical performance graphs of common-mode voltage vs. output voltage describe this behavior. These graphs are admittedly tricky to interpret and specific to power supply voltage. Only commonly used supply voltages are shown in the data sheet. Your application is unusual and will likely require additional support not related to this blog. I suggest that you please post your question with complete details on the precision amplifiers E2E forum. — Bruce, (now retired).

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

harish jangid — Thu, 10 Jul 2014 19:49:27 GMT

Hi Bruce , I am using INA129 with unbalanced supply (-V) is -2.5 and (+V) 11.5. The gain of the Differential amplifier is 50 but i am not getting the linear output after the output reach to +2.5 volt. i have applied 0 to 100 mVolt in +Vin and 0 Volt in -Vin input signal and i got 14.5 m Volt to 2.80 Volt output, what is wrong in My case??

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Vijeendra Nadgir — Wed, 19 Feb 2014 06:32:12 GMT

Thanks Bruce. Moving forward, I will post in relevant forums.

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Bruce Trump — Tue, 18 Feb 2014 20:03:07 GMT

Vijeendra-- Yes, you are correct. For the OPA547, 100mA sourcing and sinking, the minimum output voltage swing is as you state with 12V single supply. Specific product related questions would best be posted on TI's product support forums. -- Bruce

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Vijeendra Nadgir — Tue, 18 Feb 2014 13:35:39 GMT

I wanted to raise this query but I found there is a answer for similar query. Just wanted to confirm on my understanding. I am referring page 3 of OPA 547 - SBOSO56F

OUTPUT Row

If my op-amp is connected to 0V & +12 V, then I can see output only from 1.2V to 10.2V, am I Correct?

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Arun Kumar — Sun, 06 Jan 2013 04:10:01 GMT

Thank you Bruce. I had always worried about the difference between dual-supply and single-supply op amps but never found a clear answer, until now.

I love your blog.

Arun

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Bruce Trump — Thu, 04 Oct 2012 13:21:02 GMT

Ken-- There are some circuit configurations that require common-mode range that extends to, or beyond the supply rail. These circuits do not require the output of the op amp to swing beyond the rail. This would perhaps make a good future blog topic. I can't attach a figure in this comment but I can describe a simple circuit (not necessarily a common one). Visualize an inverting amplifier with the non-inverting input referenced to a fixed voltage above the rail. With sufficient voltage on the input resistor of the of the circuit, the output of the op amp will be in the linear output range of the op amp.

Regards-- Bruce

RE: Op Amp Voltage Ranges—input and output, clearing some confusion

Ken Dillinger — Thu, 04 Oct 2012 05:01:40 GMT

I am curious to know why many manufacturers are marketing their op-amps as "beyond the rails" at the inputs. The outputs cannot reach the rails, so as a buffer there is no issue with violating the input range. Unless it is with the internal design to ensure excellent CMRR, Vos, and Iib from each rail and the byproduct is a little bit of overhead. Amiright?

-Ken