chandu13:
In my case I have to use PULL DOWN resister
LPC2114 source & sink current is 5mA &V=3.3v, for how much ground current is needed for pull down
Please suggest How to calculate the pull down resister
I think in this case the size of the pulldown doesn't matter as long as it is sufficiently large. If you are using a pulldown, you don't have to worry about sinking any current into the LPC2114. You only have to worry about how much current the LPC2114 is driving. So, you don't want the resistor to sink too much current when the processor is driving 3v3.
In fact, you can probably calculate the smallest resistor permissible based upon your specs. At 5mA max drive, that means you 3v3/5mA, or 660 ohms. But since you don’t want the resistor to do anything except for when the processor is in reset, go with something big.
When the processor is in reset, you want to prevent the lines from floating. So it doesn’t matter how big or small the resistor is. It is only when actually driving do you care how big the resistor is. At 3v3, a 10k resistor only sinks 330uA (3.3/10k = 0.33 mA), and that is probably small enough. You could go larger, say 100k, and only sink 33uA. If all you are driving is the resistor and the 74LS244, I think we are fine.
(Sidebar: I’m not taking into account any leakage current into the 74LS244. I don’t know what it typically is for TTL devices (isn’t LS TTL?). But for CMOS devices (e.g. 74HC244), the leakage is so small as to be negligible. And it probably is in this case as well.)