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LMH6574

SNCS103E – NOVEMBER 2004 – REVISED AUGUST 2018

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Application Information (continued)

In such an application, the output settling may be longer than the LMH6574 switching specifications (~20ns),

while switching between two separate LMH6574 devices. The switching time limiting factor occurs when one

LMH6574 is turned off and another one is turned on, using the SD (shutdown) pin. The output settling time

consists of the time needed for the first LMH6574 to enter high impedance state plus the time required for the

second LMH6574 output to dissipate the left-over output charge of the first device (limited by the output current

capability of the second device) and the time needed to settle to the final voltage value.

While Figure 31 MUX expansion benefits from more isolation, originating from the parasitic loading of the un-

selected channels on the selected channel, afforded by individual ROUT on each multiplexer output, this

configuration does not produce the fastest transition between individual LMH6574 devices. For the fastest

transition, the configuration of Figure 32 can be used where the LMH6574 output pins are all shorted together.

Figure 32. Alternate 8:1 MUX Expansion Schematic (for Faster SD Switching)