On-Die Termination ZQ value? | Cypress Semiconductor
On-Die Termination ZQ value?
I'm quite confused by the references to ODT in the datasheets and application notes.
I'm reading this one:
and this one:
From what I can tell, the output drive impedance is set to RQ/ 5.0 (where RQ is the resistor attached between ZQ and ground). No problems. That's confirmed by looking at various other manufacturer's datasheets -- presumeably its in the standard.
So, for my board's 50R characterisitic impedance, I want to set this to 250R.
Where it gets confusing is the ODT. With the high range set, you get a receive termination of RQ / 1.66, and with the low range set you get a receiver termination of RQ / 3.33. Now, given I need 250R for my drivers, how do I get a receiver termination value of 50R to match my board's 50R traces. Surely this is about the most common impedance to design a board for?
Any clarification would be very much appreciated.