Other Parts Discussed in Thread: LMH32401
Hello I would greatly appreciate if you could comment on the following layout concerns for the LMH5401 differential buffer and the LMH32401 differential trans-impedance amplifier.
(1) For the LMH5401 differential buffer, each differential output pin has an internal buffer resistor to guard against capacitive loading and instability. Our circuit possesses an output C (equivalent) on each differential line to GND of as much as 14.6pF. Could you comment on that capacitance? Is there any chance of instability with this level of capacitive load? We could reduce this capacitance with a partial and selective GND cutout but we were hesitant to do this so far given the desire to ensure the output does not look inductive. Should we do a partial GND cutout that reduces the capacitive load somewhat? What should the maximum C be?
(2) Likewise, the inputs of the LMH5401 (IN-, IN+) have a capacitance to GND of as much as 3.8pF. Do you foresee any issues with this level of input capacitance?
(3) Finally, we are also using your LMH32401 differential TIA. This component strongly warns against output capacitive loading. We have performed a partial GND/PWR removal in the PWB at the output leads that reduces the output pin capacitance to 3.3pF on each output pin to GND. Have we removed enough of the capacitance? Are there any concerns with this level of capacitance on the output pins?
Thank You,
Jose N.