Q
A customer asked why we specify the output impedance of AD8129/30 in power-downmode as 10pF in the datasheet? Does that mean in power-down mode, the output
impedance is very high for DC and will get lower as the frequency increasing?
Would you please help to clarify this specification?
A
The PD pin on the AD8130 is only intended to save power in "Power Down" mode,and is not intended to put the output in a high-Z tri-state condition. There is
no buffer on the output to implement the high-Z state. With the PD function
asserted, what happens when another device connected to the output becomes
active depends upon a number of factors, including the magnitude and frequency
of the signal on the output of the active part. If the customer wishes to
multiplex the outputs of several AD8129/30s, the safest bet is to use a
separate device, such as an analog mux, to implement the switching function.