AD5317R internal reference buffers

I am grateful that you are paying attention to this problem.
My customers are trying to decide to connect an external reference using resistance.
I think that my customers are requesting something  evidence to design.

Best regards

Hi,

I am still looking for resources to answer your request. I'll give a reply here once they are available. May I know what are your concerns? Can the customer introduce a delay to the external reference as I have suggested before? Thanks.

Cheers,

Ivan

I was shown in the following thread that the input impedance varies depending on the selected gain.
In the data sheet, the structure of resistance strings is posted next to the figure you show.
I would like to see a mechanism by which the input impedance changes, depending on the gain chosen.

Sorry to trouble you.
I thank you in advance.

Best regards

AD5317R and external reference

https://ez.analog.com/thread/98951

I was hoping for a buffer between the Resistor String and the reference terminal.
I assume that the Resistor String and reference terminal are as direct as you say.
At that time, when connecting a resistor in series with the reference terminal, a current flows from the reference terminal to the Resistor String, so that resistance seems to influence the accuracy.
Is not there another buffer somewhere?

Best regards

Hi,

The reference section (including the ref buffer) is the same as shown in Figure 42 of the datasheet. 

Cheers,

Ivan

Hi,

The impedance change happens in the resistor string block.

Cheers,

Ivan

Hi Mochi,

the way you are dealing with this problem is not optimum, as the 1kohm resistor in series acts as a resistor divider with the internal string DAC, which in addition degrades all the specs, like drift, or gain error.

You can do couple of things,

1- add a JFET switch or similar and connect the external reference one the internal has been disable.

2- Disable the internal reference after power-up the device. During the power-up will be a short circuit but it should not be higher than few mA so, I do not believe is going to be destructive.

3- use a different DAC without internal reference.

Note- the DAC should be powered at least to the same voltage than the external reference.

Note II- why you are not using the internal reference and Gain = 2 to get a 5V output?

Regards,

Miguel

Hi,

Depending on the gain, the input impedance may affect the static performance (including accuracy) of the device which is evident on the TUE spec.

There's no other buffer in between reference block and string resistor block except the one I have shown on my previous post.

Cheers,

Ivan