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How "Rail-to-Rail" are we really talking here???.......

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Smokey:
Lets take the TL900x series:
https://www.ti.com/lit/ds/symlink/tlv9002.pdf

"TLV900x Low-Power, RRIO, 1-MHz Operational Amplifier for Cost-Sensitive Systems"

"The TLV900x family includes single (TLV9001), dual (TLV9002), and quad-channel (TLV9004) low-voltage (1.8 V to 5.5 V) operational amplifiers (op amps) with rail-to-rail input and output swing capabilities."

7.10 Electrical Characteristics:
Output:
Vo -  Voltage Output Swing from Supply Rails:
         Vs = 5.5V, RL=10K  ---> Typ 10mV, Max 20mV
         Vs = 5.5V, RL=  2K  ---> Typ 35mV, Max 55mV

So this Rail-to-Rail-Input-Output opamp can only actually get to best case output of 10mV of the rails, and worst case 55mv?

I understand this is significantly better than a nonRRIO part, but that could totally screw a design if those 10mV around zero were important. 

Note: 10mV is good, but it's not "Rail-to-Rail". 
Note2: I propose this:
For linear regulators we have "Low Drop Out".  They don't call them "Zero drop out*" ....."*still need 0.4V".
How about "RRI-LHO" = Rail-Rail-Input, Low-Headroom-Output

Shay:
Seems quite decent. I don't know any RR op-amp that can swing better than that.

Marco:
Unfortunately there's no zero ohm FETs.

Smokey:
I'm less complaining about the 10mV here, which as I said I agree is pretty good.

It's more about the advertising as RRIO as a banner spec.  There isn't even a * footnote.  Yes I know you should be reading the whole datasheet. 

I feel it's like advertising "Free Pizza Today!".  Then when you get there, it's actually $1.  That's a great price for a pizza but it's not "Free".

SiliconWizard:

--- Quote from: Smokey on March 17, 2023, 09:07:58 pm ---I understand this is significantly better than a nonRRIO part, but that could totally screw a design if those 10mV around zero were important.

--- End quote ---

Yes, this is significantly better than common, non-RRIO opamps with swings limited to hundreds of mV below rails.

The zero can't be achieved, at least not for outputs. What is zero anyway in physics? If it was 10┬ÁV rather than 10mV, would you still feel ripped off? If not, why, it's still not hitting the rails?
For inputs, some opamps actually allow going all the way down to the negative rail or even slighly lower.

The way to handle this is well known, just use power rails with a slight headroom. The benefit of using RRIO opamps even in that case is that the required headroom can be pretty small.

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