Why AD4841 is not rail-to-rail?

Hello Richie,

The problem is that you are exceeding the input voltage range of the ADA4841-2, which is on a +5V supply is -0.1V to 4V. If you want to use the ADA4841-2 to buffer the reference you’ll need to increase the power supply to at least 1V above the reference voltage.

I hope this helps.

Regards

John

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Dear JohnA

It helps for sure! However, I dont quite understand this design..

The AD7682 supports +5V voltage reference. The maximum allowed Vdd for AD7682 is 5.5V.

If I want to use it in the +5V voltage reference mode, does it mean that I need to provide at least two voltages for the system?

Thank you very much.

Best regards

Richie CHEN

Dear JohnA

Can I ask you one more question?

Can I understand it in this way: If I only want to supply the system with one kind of voltage source, I have to choose the 4.096V range. Because the maximum allowable voltage for AD7682 is 5.5V. And the voltage is not sufficient for ADA4841 to work from 0V input to +5V input.

And if I really want to use the +5V range of ADC, I have to add one more voltage source to the system, say 6V.

Thank you very much.

Best regards

Richie CHEN

Hello,

Yes your comments are exactly right. You just need to decide what option you want to use.

Regards

John

Sent from my iPhone4

Dear John, 

I have similar problem, I power ADA4841 to +3.6V, 0V. I need output voltage of 3.2V (maximum 3.6V). The maximum output voltage I get  is  2,9 V

Will I improve the output voltage if gain is greater than 1?

Are there any alternative I can put in my design that it will be rail to rail? an I can obtain 3.2 V of output voltage?

What does "rail to rail" in datasheet?

Tahnk you in advance

Thank you in advance. 

Thank you