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ID: 879
Case Type: faq
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Family: LatticeXP2

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 The XP2 device does not have a mini-LVDS output type, can I still drive mini-LVDS inputs with the XP2?

Situation:
Some devices such as the LatticeSC and LatticeECP3 have a mini-LVDS output type
while the LatticeXP2 device does not provide a mini-LVDS output type. An
application uses the LatticeXP2 device and needs the mini-LVDS output type.

Solution:
If your design is using 50 ohm PCB trace and cable impedances, you can set the
LatticeXP2 IO output type to LVDS and this will produce 400mv peak signal swing
at the receiver's 100 ohm termination with proper common mode output voltage.
The mini-LVDS specification lists 0.3v to 0.6v peak differential, so 400mv peak is
within the acceptable range for mini-LVDS.

If you have PCB trace impedances near the extremes of the mini-LVDS spec,
you can turn on the RSDS output type and add a series resistor at each of the
differential output pins located physically close to the LatticeXP2 device with
resistance value of:

Rseries = (3.167 * PCB_Z0) - 33

This will produce 600mv peak differential signal swing into the mini-LVDS receiver.
You can also lower the peak differential signal swing by raising the Rseries resistor
value. IOs set to the RSDS output type will switch over the full power supply range
into the external resistor network, so you can see higher SSO and edge skew than
when using the LVDS output type in a 50 ohm environment.
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