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SN74AVC4T234: Maximum data rate at 1.2V / 80 MHz clock and 160 Mbps DDR data rate

Ue
Genius 16285 points
Part Number: SN74AVC4T234
Other Parts Discussed in Thread: SN74AUC125, SN74AUC34, SN74AUC32

Hi all

My customer  is not sure how to read the  datasheet specification for the SN74AVC4T234: 

In the datasheet they find 100 Mbps at 1.2V.

In their design they have an 80 MHz clock and data (DDR, meaning data change at the rising and at the falling edge of the clock) with a resulting data rate of 160 Mbps per lane to be handled by the level shifter.

Are they within the specification of 100 Mbps because of the 80 MHz clock or are they above the max value because of the 160 Mbps data rate ?

Best regards

Ueli

  • +1
    Guru 242650 points

    One clock cycle consists of two pulses, high and low, which corresponds to two bits. So 80 MHz = 160 Mbps, which is too fast for this device.

    Better use a low-voltage logic family like AUC. For level-shifting to a lower voltage, you can simply use a buffer with overvoltage-tolerant inputs, e.g., SN74AUC34 or SN74AUC125.

  • 0 in reply to Clemens Ladisch
    TI__Genius 16285 points

    Hello Clemens

    Thank you for the quick reply !

    Best regards

    Ueli

  • 0 in reply to Ue
    TI__Genius 16285 points

    Hello Clemens

    Here comes the customer feedback:

    ----------------------------

    They find it is not clear that the AUC are really faster than the AVC for their supply voltages. Further below the TPD resp. TPHL/TPLH values for the AUC34 and the AVC4T234 are copied. There is only a difference of 100 - 200 ps. Moreover the max data rate is not specified for the AUC devices. Considering the AUC is specified for 1.2V with CL=15pF/2kOhm and the AVC with CL=30pF/500Ohm there seems no difference. They have to base their design on the max values.

    ----------------------------

    Please comment if their understanding is correct.

    Best regards

    Ueli

    SN74AUC32

    SN74AVC4T234

  • 0 in reply to Ue
    Guru 242650 points

    The worst case of 1.2 V ± 0.1 V is 1.1 V. For that voltage, AVC does not specify a maximum, while AUC's maximum is smaller than AVC's typical value.

    I do not know where those Mbps values in the AVC datasheet come from. I do not see a strong correlation with the propagation delay.