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DS08MB200: Output termination setting for DS08MB200TSQ/NOPB

Masashi Koike
Prodigy 10 points
Part Number: DS08MB200

Tool/software:

I have some questions regarding your product, DS08MB200TSQ/NOPB, and I would appreciate your guidance.

[Target Product]
DS08MB200TSQ/NOPB

[Questions]
Could you please provide guidance on the termination method for LVDS output usage of this product?
My understanding is that there is no internal termination resistor in the output stage of this product. Is this correct?

[Background]
We intend to input an LVDS signal into this product and output the signal in LVDS. The input system of this product has a characteristic impedance of 100Ω, and the output device requires an input characteristic impedance of 100Ω. Therefore, we plan to use 100Ω termination for both the input and output of this product.

The device at output of DS08MB200TSQ/NOPB does not have internal termination in the input stage (based on the specification sheet and actual component measurements), and it appears that there is no internal termination resistor in the output stage of DS08MB200TSQ/NOPB (based on the datasheet). Therefore, we planned to use external termination (100Ω) between the output of this product and the input of the other device.

However, when we created the actual circuit, the termination resistance between the signal P/N in the above path was 50-52Ω, suggesting that the external termination resistor of 100Ω is being combined with another resistance component. When the circuit is operated, it oscillates at approximately 5.3MHz. When the external termination resistor is removed, the termination resistance between the signal P/N in the above path becomes approximately 100Ω, and the oscillation stops.

  • +1
    TI__Guru 72741 points
    Masashi Koike said:
    The device at output of DS08MB200TSQ/NOPB does not have internal termination in the input stage (based on the specification sheet and actual component measurements)

    I think we're saying the same thing here but the input pins denoted as LIx and SIx have internal termination. The output pins defined as LOx and SOx do not have termination. 

    Masashi Koike said:
    Therefore, we planned to use external termination (100Ω) between the output of this product and the input of the other device.

    For LVDS buses, you normally only terminate at the point furthest away from the driver (at the receiver node). If you place a 100 ohm resistor at the output, it will weaken the VoD and limit the speed/distance it can communicate. I normally only terminate the output in a MLVDS bus.

    Masashi Koike said:
    When the external termination resistor is removed, the termination resistance between the signal P/N in the above path becomes approximately 100Ω, and the oscillation stops.

    I don't think you should be placing termination on both sides the bus in the LVDS system. I'm not entirely sure why its oscillating but it may be due to resonance of an RLC circuit (cabling has inductance and capacitance, with the resistor you're likely hitting a frequency where the system becomes unstable).

    -Bobby