Other Parts Discussed in Thread: ADS8588S, ADS8598H
[1]
Question regarding the capacitance on the REFCAPA and REFCAPB pins to REFGND.
- Pin Functions section of the DS states :
This pin must be shorted to REFCAPB and decoupled to AGND using a low ESR, 22-µF ceramic capacitor.
- Electrical Characteristics section of the DS states recommended typical capacitance of 10uF for C(refcap)
- Section 7.3.8 in the DS states:
The REFCAPA (pin 45) and REFCAPB (pin 44) pins must be shorted together externally and a ceramic capacitor of 10 µF (minimum) must be connected between this node and REFGND (pin 43) to ensure that the internal reference buffer is operating as closed loop.
- The Figure 57 and Figure 61 in the DS show 22uF
- The EVM uses 10uF
Which value is correct? When would you use a higher capacitance? If you have the board space, is the higher capacitance better?
[2]
Figure 61 shows for an external reference voltage, you need Cref to filter the reference voltage noise.
- Are there any guidelines on choosing this capacitance?
- Figure 65 shows both Cref on the external reference output, and a 100nF on the ADC REFIN/REFOUT pin. Is this the proper setup, and the Cref is generally 10uF?
[3]
If the serial interface is used (vs parallel interface), and DOUTB not needed, can this pin be left floating?
[4]
There was trouble with a different ADC in previous-gen equipment, where when a sensor was connected to the ADC, and power from the sensor was supplied to the inputs of the ADC before the ADC was powered, the ADC wouldn't function correctly. For the ADS8588H, are there any requirements about there being voltages applied to the ADC inputs before the device has powered up?
Thanks,
Darren
