Hi Team,
Please let me me confirm about the pull down resistor for the 4 level input pins.
There is table 1 in the datasheet page 12. For R, the recommended pull down resistor is 20kohm. If the customer cannot use 20kohm, the choice would be 22kohm or 18kohm.
I believe these 22k or 18k ohm resistor are acceptable, but could you give me your opinion ?
Best Regards,
Kawai
Hello Kawai-san,
The DS80PCI402 does not have a complete description of the 4-level input pins, and we intend to update this datasheet to include this information in the future.
For now, I would like to refer you to the Feature Description section (Section 7.3 Page 14) of the DS80PCI810 datasheet. This section provides a detailed explanation of how the internal pull-up/pull-down is set up. “There is an internal 30 kΩ pull-up and a 60 kΩ pull-down connected to the package pin.” This section also provides where the thresholds fall between the 4 levels.
Based on this information, we can determine if these resistors would be acceptable.
Let us assume that we have a 3.3 V power supply. This means that the threshold between 0 and R would be 0.66 V and the threshold between R and F would be 1.65 V. As long as we fall between these two voltages, then the pin level will be R. When adding a 20 kΩ to ground, we can determine the voltage at the output based on adding a resistor in parallel with the 60 kΩ pull-down resistor, and this would give 1.1 V at the output.
By a similar calculation with an 18 kΩ resistor, the voltage would be approximately 1.04 V, and with a 22 kΩ resistor the voltage would be approximately 1.15 V. Both of these fall well within the threshold for the R level, and therefore either of these resistors would be acceptable.
If you are using a 2.5 V power supply, then a similar calculation would be applicable.
Best,
Michael
High Speed Datapath Solutions
Analog Factory Applications
