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Input levels for LVDS driver

Avi Chami1
Mastermind 7395 points
Other Parts Discussed in Thread: SN65LVDS1, SN65LVDS4, SN74AVC1T45

Hi,

The SN65LVDS1 is defined for Vcc operation of down to 2.4V. It is also defined as a complementary of 2.5V capable SN65LVDS4.

However, Voh is defined as 2V irrespective of Vcc.

I would like to use this device for 2.5V LVCMOS, and for that purpose I would expect Vih to be defined as approx. 1.7V, for Vcc=2.5V. Can you please tell me what would be Vih and Vil for Vcc = 2.5V?

Thanks!

  • 0
    TI__Expert 4990 points

    Hi,

    the SN65LVDS1 is a driver with a LVTTL Input. For LVTTL Inputs the VIHmin is defined with 2V, VILmax with 0.8V as mentioned in the datasheet on page 4.

    As you can see in attached picture, VOHmin of 2.5V CMOS is defined with 2.3V and VOLmax is defined with 0.2Vthe 1.7V you mention is a VIHmin for LVCMOS Input. As you can see in the pictuure in the top right corner, you can use the 2.5VCMOS Output (Driver) of your device to a LVTTL Input (Receiver).

    So, the important thing to mix with different LogicLevels is, that VOH is higher than VIH and that VOL is less than VIL. Also important is, that the maximum Output Voltage is not higher than the maximum Input Voltage (VIH Tolerance).

    Regards,

    MIchael

  • 0 in reply to Michael M.
    Mastermind 7395 points

    Thank you for your fast response.

    LVCMOS-2.5V levels are defined on Jedec standard JESD8-5A.01. This standard defines that Voh, for light loads, is 2.1V. And it defines Vih to be 1.7V. The reason for that is to ensure a noise margin of 0.4V, which is a common noise margin for many digital families. I understand that TI parts Voh is 2.3V, but that is more than the standard demands.

    My customer is using a non TI device which complies with LVCMOS Voh of 2.1V, and he needs to connect that output to an LVDS driver. He feels not confortable (and I think that he is right) with a noise margin of only 0.1V, as would be the case if he used the SN65LVDS1 driver. The reason for my question was that SN65LVDS1 is defined for very low operating voltage, so I was hoping that you may have tested it in the past for LVCMOS-2.5V levels compliance. It this is not the case, and the Vih level is indeed 2V as stated in the datasheet, my customer won't be able to use this part.

    All the best,

    Albert

  • 0 in reply to Avi Chami1
    Intellectual 310 points

    Maybe you can use SN74AVC1T45 to level shift the 2.1V signal.