opamp output clips far from rail values

[hani nik]

Hello all.

I am using a CMOS opamp with power supply 0 to 3 V. The opamp is used as a buffer with the output driving a transducer input based on the signal fed to the non-inverting input. My problem is that the output clips at 1.8 V. I need to drive it op to 2.6 V or so.

I know the output clips at a certain point but I thought it would be close to the power rails. The opamp is suppose to be able to produce close to rail-to-rail output.

Is this normal?

Thank you.

 

[echo47]

It may be normal. What type of opamp is it? How much current is it driving into the load?

 

[hani nik]

It is OPA2336PA.
How do I check how much current it drives into the load? Find the resistance of the load and then apply V=IR?

 

[echo47]

If your load is resistive, then V=IR will work fine.

The TI data sheet shows two graphs, "OUTPUT VOLTAGE SWING vs OUTPUT CURRENT". Although the graphs are for a different power supply voltage than your 3V, you'll see that even a few milliamps of load causes the output voltage to drop significantly. That could be your problem.
https://focus.ti.com/docs/prod/folders/print/opa2336.html

Also, if you signal is at too high a frequency, the output voltage won't reach rail-to-rail. See graph "MAXIMUM OUTPUT VOLTAGE vs FREQUENCY".

 

[FvM]

Also, if you signal is at too high a frequency, the output voltage won't reach rail-to-rail. See graph "MAXIMUM OUTPUT VOLTAGE vs FREQUENCY".

Yes, but this effect can clearly be distinguished from clipping as it is caused by slew rate limitations. The latter produces a triangular waveform.

P.S.: You said, your operating the OP as a buffer. Then the said behaviour is expectable from the datasheet, cause the amplifier is not input rail-to-rail.