OP-Amp NCS20071 not reaching rail, as per datasheet.

[Jdtech]

Hi,
I have a On-Semi Opamp. NCS20071 SN2T1G. In a test circuit on the bench I cannot get the output to swing to within what I believethe spec states.
datasheet

Supply is 5V, in a voltage follower configuration. Output also feeds the inverting (-) input, varying Input signal to non-inverting (+) input.
Using a pot to sweep the input voltage 0.2 to 4.8v. the output will not go above 4.25V.
Datasheet page 8 gives,
Output Voltage High (VOH) Voltage output swing from positive rail 0.013V typical, 0.20V max.
So I assume that I should be able to drive to output to within 0.2V of the supply...or am I wrong?

My output will not go nearer than 750mv from the high rail. I tried with a supply of 10V and still can only get output to within 0.7V of the supply.
Swinging to low rail is fine.
I'm not an analog guy by any strectch but I've thrown a couple of hours at this on the bench and just can't see where I'm going wrong.
Or am I miss reading the datasheet?
Any guidance appreciated. J.

 

[barry]

They don't specify input common-mode range (at least, I couldn't find it) but I suspect your problem is that this is a rail-to-rail OUTPUT device, NOT!!! rail-to-rail input.

Try putting some gain in your circuit and I'll bet the output will go to the rail.

Update: Just found it on page 5

Input Common Mode Voltage Range VCM VSS VDD − 1.35

 

[KlausST]

Hi,

Using a pot to sweep the input voltage 0.2 to 4.8v. the output will not go above 4.25V.

The problem is not the "output", the problem is the "input". This is no "rail-to-rail input OPAMP.
--> The "common mode input voltage range" is limited to: VDD-1.35V

So in inverting mode or in gain >1 mode the output may swing very close to VDD.

Klaus

added:
@barry: V_CM is specified on page 5: OPERATING RANGES

 

[Jdtech]

Thanks Guys,
I'll go have a read up on those aspects.
J.