Can 74VHC4040 work at 250MHz clock input ?? Anyone?

[europus2002]

Hi all,
I have a situation here...I am trying to do some very precise frequency counting. I am trying to use 74VHC4040 in the design at 250MHz with gate charge dissipation resistor to ground (47Ohm) at clock input.will that work? 74VHC4040 spec sheet says Fmax=210MHz...Has anyone used this config before? or have any suggestions...I am trying to take count output on latches only when the counting is over....Let me know if more info i needed.

 

[itsmoked]

Is this a one-off? You'd be insane to base a product on this. Not only is your desired speed 19% over the absolute maximum but it's 208% over the maximum over temperature!!

That said if you raise the voltage further you might have a better chance on a one-off. Notice how much faster the part gets with voltage. Maybe run it at 6.8V - you might get to 250Mhz. Otherwise just get the smallest CPLD or FPGA and define a 4040 in it that will run at 2-3Ghz.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[logbook]

Looking at the Fairchild data sheet the minimum guaranteed operating frequency is 150MHz at 5V with minimum load capacitance. Don't bother, even for a one off. It just won't be reliable. Use a divide by two pre-scaler in front of it to make it useable.

 

[logbook]

Consider using a Philips/NXP 74ALVC74 as a divide by 2 pre-scalar. This will run above 300MHz at 3.3V according to the datasheet.

 

[IRstuff]

Not a problem, IF you run it at something like -20ºC. CMOS runs faster at colder temperatures.

TTFN

FAQ731-376

 

[europus2002]

Thank you all....I decided to prescale both input frequencies / 16 and they both should work good with that chip....Just for sharing with you guys , I did few tests and 74VHC4040 does work at 250MHz without a problem provided you have gate charge dissipation resistor. But cannot risk it letting it out for manufacturing. I mainly decided not to use that since there was skew in the output when i pushed it to 200MHz and above limit.....I needed skew to be less than 0.01% & it turned out to be 0.05% and the only capacitance in the output was that of oscilloscope probe (~10pF)..... Thanks again for sharing with me your thoughts....