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66AK2G12: Confirmation about QSPI switching characteristic

Naoki Kawada
Guru 19890 points

Part Number: 66AK2G12

Hi,

My customer is now checking QSPI switching characteristic on their own board with 66AK2G12 and found that they have not been able to meet the requirement of Q2 (Pulse duration, QSPI_CLK low) if they are compliant with VIL(0.8V) based measurement. But if 1.6V based (center voltage of IO), they can meet the spec. Please take a look at the following captures.  

Please note that they have followed the all of length matching recommendations described in the the following document:

http://www.ti.com/lit/an/sprac54a/sprac54a.pdf

2.17 QSPI

The question here is, should they measure low pulse clock duration based on its VIL ?  Could you please confirm ? As for the clock waveform, it looks not so bad to me. 

Best Regards,
NK    

  • 0
    TI__Mastermind 42545 points

    Hi Naoki,

    The duty cycle is relative to the thresholds for both Vih and Vil. You can't measure at the voltage level for Vil since internally the device will not register a high until the rising edge reaches the Vih value of 2V.  Normally if the rising and falling edges are approximately the same slope you can measure at the voltage that is half way between Vil and Vih or, in this case, 1.4V.  If the slopes are not the same you can measure from the point where the signal passes Vil on the falling edge to the point where it passes Vih on the rising edge.

    Regards, Bill

  • 0 in reply to Bill Taboada
    Guru 19890 points
    Hello Bill,
    Thanks for your reply. This answers to their question. I close the thread now.

    Best Regards,
    NK