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# LMK1C1104: sinewave input/maximum input slew rate

Part Number: LMK1C1104

I would like to use the LMK1C1104 with either an LVCMOS or sinewave input at 40MHz. With a 3.3V supply, what is the MAXIMUM input slew rate, i.e., will it work with a sinewave? The data sheet only specifies minimum slew rate.

• I think I misstated this question. What is the maximum input RISE TIME (inverse of slew rate). If I read the data sheet correctly, a minimum slew rate of 0.1V/ns implies that my 40MHz sinewave won't work with this part. Am I correct?

• Hi Barry,

The slew rate specification is for 20% to 80%.  So a sine wave actually does get moving well enough here that at 40 MHz you can meet the slew rate specification.  For example:

40 MHz @ 3.3 V from 20% to 80% is 0.387 V/ns, risetime = 5.1 ns
40 MHz @ 2.5 V from 20% to 80% is 0.293 V/ns, risetime = 5.1 ns
40 MHz @ 1.8 V from 20% to 80% is 0.211 V/ns. risetime = 5.1 ns

As for maximum rise time, since we specify slew rate, the maximum allowable rise time becomes a function of amplitude.  The larger amplitudes have longer allowed rise times.  In my example above, the slew rate increases because I hold the frequency (which is associated with rise time) constant while increasing amplitude.
So for a 3.3 V signal, a 10.5 MHz sinewave would have just over a 0.1 V/ns slew rate with a rise time of 19.5 ns.
For a 1.8 V signal, a 19 MHz sinewave would have about 0.1 V/ns slew rate with a rise time of 10.8 ns.

Of course supply isn't always exactly 3.3 V or 1.8 V.

Hope this helps.

73,
Timothy

• Thanks, Timothy.

I wasn't thinking quite clearly (apparently) when I posted this. This makes perfect sense.

TU,

Barry