# How can I determine whether this is a “rail to rail” opamp from its datasheet?

I know that rail to rail means that the opamp output can have a swing upto its power rail voltages.

So for a rail to rail opamp lets say if the supply test condition is +-12V, I would assume that the output swing can reach upto +12V or down to -12V. Similarly with a +-15V supply the swing would reach upto +15V or down to -15V.

But nowhere in this datasheet "rail to rail" phrase is indicated.

In electrical characteristics I can only see some section called "Maximum peak output voltage swing" without any given supply voltage condition.

So briefly, I'm not able to verify whether this opamp is rail to rail and I guess don't know to focus on the right parameters.

How can it be inferred from this datasheet whether this opamp is rail to rail?

• The table in 6.5 has the Vcc mentioned at the top (+/- 15V) – ratchet freak Oct 1 '18 at 8:52
• I see so can we say it can typically swing between +13.5V and -13.5V for a supply voltage +/- 15V? So not a rail to rail opamp? – floppy380 Oct 1 '18 at 8:55
• @ratchetfreak Please keep your answers to the answers section. As you can see, your comment is now starting a possibly lengthy discussion from OP, and you can not edit your comment to clarify, nor can the user accept your answer. – pipe Oct 1 '18 at 9:06
• Rail-to-Rail means NOTHING! It is marketing, and is used in descriptions to imply that either/both inputs or outputs get close to the rails (by some amount that is not typically advertised). You must check the datasheet carefully (as shown in the answers). Manufacturers could label any of their products as having 'rail-to-rail' I/O. – Chris Knudsen Oct 1 '18 at 15:10

## 3 Answers

Try this: -

For a power rail of +/- 15 volts the input common mode range is only guaranteed to be +/- 11 volts.

For a light load on the output pin (10 kohm) the output is only guaranteed to swing +/- 12 volts.

An R2R op-amp will never output swing completely to the rails but you could expect it to get within 100 mV on a light load.

Conclusion - this op-amp is NOT an R2R device.

• Max peak output voltage is more straightforward. But what is really meant by "common mode input voltage range" in this context? – floppy380 Oct 1 '18 at 9:16
• @user1234 it's the voltage range that the op-amp inputs has to be constrained within if you are to expect op-amp functionality. – Andy aka Oct 1 '18 at 9:52

Most manufacturers specifically label their op-amps to be "rail-to-rail" if they're capable of such.

Under Typical Characteristics, Figure 2 shows you what the output voltage is for a given VCC. So for a VCC of 15V, the best output you'll get is approx ~+12V.

So it is not a rail-to-rail op-amp.

• Rail to rail on the output is not the same as rail to rail on the input, and vice versa. Many fall into that trap. – Scott Seidman Oct 1 '18 at 11:02

Vicr and Vom are the parameters to look at. In a rail to rail op amp, these will go all the way to the rails. The table lists the supply voltage at the top (+/- 15v). Spoiler alert : this is definitely not a rail to rail op amp.