The AD777x already integrates a 2.5V +-10ppm reference. The reference is internally buffered and available at Pin REFOUT.
The buffers can be set in three different modes.
- In Fully enable mode, no external buffer is required since the current is provided by the internal buffer.
- In Bypass mode, the internal buffer is bypassed, so the high frequency currents are provided by the external capacitors connected to the REFx+ and REFx- pins. In this case it is recommended to use an external buffer if a low noise reference is required.
- In buffer precharge (pre-Q) mode, the internal buffer is connected during the initial acquisition time to precharge the internal ADC reference capacitor. During the final phase, the reference is connected directly to the ADC external capacitors, reducing the current requirements.
For more information, please read “Internal Reference and Buffers” section.