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Original question:

DS90LV804: Some questions

DS90LV804: Double Termination Question

Bernard Regier
Prodigy 10 points
Part Number: DS90LV804

Tool/software:

The TX of the DS90LV804 shows an internal 100ohm termination resistor. With a normal configuration 100ohm termination at the RX side would this put two 100ohm resistors in parallel; the internal and external making the transmission line 50ohm differential termination instead of 100ohm? Is the DS90LV804 designed to handle 50ohm differential termination and still drive the lines within nominal LVDS logic levels (VOL 1.0V, VOH 1.4V)?

I'm guessing I will also want to add the extra 100ohm termination resistor at the RX side of the transmission line.

  • 0
    TI__Genius 15321 points

    Hello, 

    I am checking on this and I will get back to you tomorrow. 

    Thanks, Amy

  • 0
    Guru 316760 points

    Each individual termination resistor (at each end of the cable/trace) should match the characteristic impedance of the cable/trace. For LVDS, this is usually 100 Ω, so this is OK. (You would have a problem only if you had two 100 Ω resistors at the same place.)

    LVDS usually uses unidirectional point-to-point connections, which need only a single termination at the receiver. With two resistors, the current will be higher, but this device is designed for that: VOD is specified with both internal and external resistors present.

  • 0
    TI__Genius 15321 points

    Hi Bernard,

    This device is a buffer. There is a section in the datasheet called OUTPUT INTERFACING that mentions, "outputs signals are compliant to the LVDS standard", and the lines will be driven to the levels described in LVDS OUTPUT DC SPECIFICATIONS (OUTn±) (datasheet pg. 3). There is no need to add an extra termination resistor at the RX side of the transmission line, unless you are terminating the end of the bus (see the OUTPUT INTERFACING section). 

    Best Regards, Amy