I am having trouble understanding the function of the optional buffers between the PGA and ADC on the ADuCM360. It seems the buffers cannot be used at all for Gain=1 when the PGA is off due to a silicon error so I think that the ADC sees the MUX output completely buffered. For PGA gain >2 you can enable the buffer but doesn't the PGA already serve as a buffer between the input and the ADC? What purpose does adding the additional buffer serve. Is the PGA output impedance too high to drive the ADC? It is not clear from the datasheet and manual when you would want to use this feature which increases power consumption.
Your understand is right. For Gain=1, the buffer cannot be used, but this feature is enabled in ADuCM362/3. So if you use this feature, you can choose ADuCM362/3.
For PGA gain>2, the PGA can serve as a buffer, so the buffer isn't necessary. If you use the buffer, it will add noise, but the linearity will be a little better. The recommended way is disable the buffer when PGA gain >2.
HI Barry,Can you comment on what type of issue the device will have when using the PGA Gain =1?Is it just poor linearity or is it something very bad where the ADCs readings are all over the place?We have a customer that will likely shift to the 362 but he has a bunch of boards where he'd like to use the Gain=1 setting for a coarse measurement. If it's 10-bits accuracy, this might be good enough.
When PGA gain =1, the buffer cannot be enabled. So the input current will be bigger (500nA/V), while the input current will be 1nA typ when buffer is enabled.
You need to consider is the input current has effect on your whole system.