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AM3517 IBIS Model - I2C SCL/SDA Not Behaving as Expected

John Morton
Prodigy 150 points
Other Parts Discussed in Thread: AM3517

Hello,

  I am performing Hyperlynx simulations on I2C2 and I2C3 using am3517_zcn.ibs, v4.1 10-May-2010 and am getting some unexpected results. In a nutshell, it appears the drivers for I2C2_SCL, I2C3_SCL, I2C2_SDA, and I2C3_SDA are performing like totem pole outputs instead of open drain.
   

  I am selecting Model_22 I/O, 3.3V, PD for my simulation. What leads me to say I think these drivers are behaving like totem pole outputs is that the rise time is quite fast, approx. 3ns. An open drain output with a 4.7k pull-up should have resulted in a 200 ~ 250ns rise time, I would think.

   I'm pretty sure the silicon is performing as open drain for the I2C ports as we've been interfacing successfully with a variety of I2C peripherals. I don't think they would work if the AM3517 I2C pins were totem pole.

  This leads me to believe there's a problem with the IBIS model.


Thanks,

John M.