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TLK1201AI vs. TNETE2201 - Input and output termination recommendations
Reposted from e-mail correspondence:
Have another question regarding the TLK1201AI. The data sheet states that no pull-down resistors are needed on the TXP/TXN outputs. (Its on page two towards the bottom where the differences between TLK1201A/AI and the TNETE2201). It also does not show any termination in Figure 12, the typical application circuit, like is shows for the RXP/RXN inputs. I just wanted to verify that if I am using this part for a Fibre Channel design that won't need any terminations. Can you please verify this for me?
Yes, the information in the TLK1201AI datasheet is correct. The TNETE2201 uses a typical LVPECL output structure, and when AC-coupled requires source termination of 150 to 220 Ω to ground in order to drive falling edges. The TLK2201AI is a newer device that uses an LVPECL-compatible VML output stage which is capable of driving both rising and falling edges. Because of this, pull-down resistors are not required on TXP/TXN outputs. Termination resistors are still necessary at the RXP/RXN inputs in order to match the transmission line impedance and prevent signal reflections. The configuration shown in Figure 12 of the data sheet is recommended.
Let me know if you have any additional questions.
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