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Altera_Forum
Honored Contributor I
1,260 Views

Cyclone III 3.3V LVTTL/LVCMOS input impedance

I have a customer that has an unusual driver arrangement for a couple Cyclone III 3.3V LVTTL/LVCMOS inputs and they want to know what the Cyclone III input impedance will be. Digging through the Altera info pile I found numbers specified for an output driver and an447 discusses PCB trace impedances and series resistor values, but have not come up with a specified value (range) for the input impedance. Cyclone III part number: EP3C25U256I6N. 

Thanks in advance for the help.
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Altera_Forum
Honored Contributor I
120 Views

LVTTL/LVCMOS means high input impedance, the input pin impedance can be best modeled by a small capacitance of 5 - 6 pF, see datasheet table "Cyclone III Devices Pin Capacitance".

Altera_Forum
Honored Contributor I
120 Views

 

--- Quote Start ---  

LVTTL/LVCMOS means high input impedance, the input pin impedance can be best modeled by a small capacitance of 5 - 6 pF, see datasheet table "Cyclone III Devices Pin Capacitance". 

--- Quote End ---  

 

 

Thanks FvM. 

I am looking for a quantitative numeric value/range rather than a generic word description that can be interpreted multiple ways. While I do appreciate it can be modeled, the results are only as good as the input to the model and I would think that Altera can supply the needed details.  

Regards.
Altera_Forum
Honored Contributor I
120 Views

Your comment is rather unspecific und doesn't actually tell which kind of model parameters you are looking for and in which frequency and input voltage range you want to model the input pin behavior. There are different quantitative data available from Altera. In particularly you have: 

- datasheet specifications 

- IBIS files 

- HSPICE models (encrypted)
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