CMOS drive to capacitor

[sijukrishnan]

Timing is not critical, but how I decide magnitude of capacitance that can be connected to a CMOS output?
I want, 2.5V CMOS IO to drive 8 CMOS devices having a total loading of 22pf capacitance. Do you recommend a direct connection?

Thanks

 

[erikl]

Timing is not critical
I want, 2.5V CMOS IO to drive 8 CMOS devices having a total loading of 22pf capacitance. Do you recommend a direct connection?

No problem, as "timing is not critical".

 

[sijukrishnan]

Thank you for your answer, but let me clarify to the fullest. When the output switches state, momentarily capacitor would become short circuited if the transition time is very fast. Mightn't this surge in the capacitor load damage the device?

 

[erikl]

Mightn't this surge in the capacitor load damage the device?

No: there's always a driver output resistance which limits the output current to a max. value which is harmless.

High fanout (in your case: only 8) -- apart from timing -- is only a problem for very high values, like feeding 10000 flip-flop reset inputs from a single feeble driver (fanout=10000). This could make the ramp so slow, that the cross currents through the (10000) input buffers could break down the power supply.

 

[sijukrishnan]

>>there's always a driver output resistance which limits the output current to a max. value which is harmless.
So momentary loading will not damage the output right? Thank you very much erik, gathered valuable info from you.

 

[leo_o2]

Yes, momentory loading might not damage it.