Other Parts Discussed in Thread: LMK04828, DAC38RF83
Hi,
I am referencing section 7.4 on page 14 of this document:
It mentions using a network with 1150ohm pullup on SYSREF+ and 453 pulldown on SYSREF- to create a fixed VOL for times when SYSREF is not driven.
I wanted to confirm, isn't this backwards? If you are pulling SYSREF+ up and you are pulling SYSREF- down, wouldn't this create a VOH scenario with a positive differential voltage across the inputs from + to -? Wouldn't this leave the SYSREF input as "asserted" or logic high? Why would the reverse not be done, with SYSREF- pulled above SYSREF+ to leave the SYSREF differential input biased in the logic low, or unasserted state with a negative differential voltage across the inputs from + to -?
I have setup with driver with ~2.2V Common mode and ~0.75V to 1.2V differential swing for SYSREF so I believe AC coupled approach is necessary as resistor divider to bring the common mode down to 0.5V (the SYSREF input common mode spec for the DAC38RF89) would cause too much signal attentuation