Dear Analog Devices

I am having challenge in understanding the datasheet on the ADA4807 (alternative AD8027), in respect of the output swing.

My challenge is that I have an input from a potmeter, providing a voltage input to a “buffer”, using an opamp (ADA4841-1YRJZ) with gain +1. The voltage source to the amplifier is a filtered +5V. The signal into the amplifier is in the range of 0V to +5V, where I need the output from the opamp to be as close to the 0V to +5V as possible. Using the ADA4841, the output only rise to 4.2V. I am therefore considering to use the ADA4807 (alternative AD8027) as replacements, being able to change the component only, not needing to change the PCB layout footprint. The time and cost is crucial.

Is it possible to give me a feedback on the actual expected output swing when using a +5V power source, and an input signal of 0V to +5V?

Regards

K

• Konta,

Op amps can be RR output but not RR input.  Look at the data sheets to determine.

The 4841 has a guaranteed input voltage range of 0-4V, so that's why you see 4.2V.

WRT output swing, for RR outputs, the transistors are either common emitter or common source.

So you can get within a Vce(sat) or an Rds(on)*ILoad, so it depends on what your load is.

If it's high, say 100kohms, you could probably get within 100-200mV of either rail.

Harry

• Hi Konta,

If you are using a single supply of 5V in your opamp, and apply a signal of 0-5V at a gain of 1. It does not necessarily mean it will produce an exact output of 0-5V. It is usually i little above the minimum signal and a little below the max, its because of the headroom voltages in the amplifier. As you can see in the datasheet the output voltage swing of the opamp in a 5V single supply at a gain of 1 is typically between 0.029 to 4.974 and considering that you filtered the supplies, the range would decrease. I would suggest that you would increase your voltage supply if you want to achieve a 0-5V output swing.

Regards,

Roel

• Depending on the source impedance, i.e. the resistance of your pot, and the maximum signal and conversion frequencies (likely to be pretty low considering a pot is the source), you might not need any buffer amplifier to drive the ADC. Try a wire instead ;-).

You likely want to add some ESD protection, but that should be there no matter what.

Klaus

• Hi and thank you for the feedback

I tested the ADA4807-1ARJZ and it worked just fine. The same footprint did not require a new layout.

I appreciate the feedback from you all, thank you

Regards

Konta

• This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

Thank you,