The RFB of the LTC2757

Hi UBOTI 

UBOTI said:

Q1:The RFB of the LTC2757 is 10KΩ (TYP) in the table specs, but can it be changed by setting the output voltage span?

The resistance of RFB is constant regardless of the output voltage span. 

Not sure what you meant by Q2, could you elaborate?

Best regards,

Ian

Used for connection of data sheet P1.
It will be used in applications that emphasize responsiveness.
The time constant is determined by Rfb and 27pF of the external capacitor.

When I checked the waveform, I thought that Rfb was different because it did not match the calculated value.

There is a link on the product introduction website, and if you look at the explanation of the LTC2757 introduction video, it explains that Rfb changes depending on the output span setting.

www.analog.com/.../5579239875001.html

I'm sorry to trouble you, but could you please check again?

Used for connection of data sheet P1.
It will be used in applications that emphasize responsiveness.
The time constant is determined by Rfb and 27pF of the external capacitor.

When I checked the waveform, I thought that Rfb was different because it did not match the calculated value.

There is a link on the product introduction website, and if you look at the explanation of the LTC2757 introduction video, it explains that Rfb changes depending on the output span setting.

www.analog.com/.../5579239875001.html

I'm sorry to trouble you, but could you please check again?

We've tried to reach out to the design team to check on this. I'll let you know when there is an update. 

Hi UBOTI I was just checking this and wanted to confirm, when you are testing the time constant, does it change depending on the output span setting? (same vout step value) Also, I noticed that RFB value is a typical spec which means it could vary on units, the guaranteed spec is the minimum which is 8k ohm.

The responsiveness of the output would largely rely on the settling time and response of the output amplifier used. From the datasheet, when LTC1468 is used wi a Cfb of 27pF, a 1.8us @ 0.0004% accuracy can be achieved. a good read would be  AN120 - 1ppm Settling Time Measurement for a Monolithic 18-Bit DAC (analog.com)

Yes, changing the span setting will change the time constant.
So Rfb changes