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DS90CR288A: The LVDS question for DS90CR288A

Mickey Zhang
Genius 12080 points
Part Number: DS90CR288A
Other Parts Discussed in Thread: DS90CR482

Hi team,

The customer would like to use DS90CR288A. The DS90CR288A datasheet shows the Receiver Input Range Voltage is 0~2.4V

and the Differential Input High Threshold is -100mV~100mV.  For the 0~2.4V input voltage, my understanding is 

the common voltage range of the RxINx+ pin or the the RxINx- pin. And the 0~2.4V input voltage can meet the TIA/EIA-644 LVDS Standard.

Q1. Is my understanding correct?

Q2. The customer said there were 2.5VLVDS standard, 3.3VLVDS standard and 5VLVDS standard. I think 2.5V, 3.3V or 5V is

indicated the VCC voltage. Is this correct? Would you explain the 2.5VLVDS standard, 3.3VLVDS standard and 5VLVDS standard?

Q3. The customer's input common voltage is 2.5V. It is above 2.4V. So DS90CR288A cannot meet his requirement.

So he needs to verify if we have the similar device that  can meet the 2.5V input common voltage.

If my above understanding is correct, this mean we do not have the device which can meet the customer's input common voltage.

Would you help me to verify this?

Q4. However, I note DS90CR482. The Absolute Maximum Ratings shows the e Receiver Input Range Voltage is -0.3V~3.6V. 

Can DS90CR482 meet the customer's requirement that the input common voltage is 2.5V?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

  • 0
    TI__Genius 12080 points
    Hi team,

    Would you provide some suggestions for my questions?
  • 0 in reply to Mickey Zhang
    TI__Genius 10250 points
    Hi Mickey,

    I am looking at this and will get back to you today.

    Yaser
  • 0 in reply to Yaser Ibrahim
    TI__Genius 10250 points

    Q1. Correct

    Q2. Correct. These are Vcc voltages.  There is no separate standard for 2.5, 3.3 or 5V supply.  In all cases the LVDS receiver needs to support 0 to 2.4V common mode and 100 mV differential voltage threshold.

    There are variations of LVDS for lower common mode, e. g. sub-LVDS which uses 0.9V common mode (typical, instead of 1.2V in LVDS).

    Q3. The LVDS driver should have a typical common mode voltage of 1.2V. To allow for up to  1V of ground voltage difference, the driver common mode voltage needs to be between 1V and 1.4V.  This will make sure that the receiver will see a common mode of 0 to 2.4 V. The diagram below shows how this works.

    Q4. The Abs Max LVDS Receiver Input Voltage for DS90CR288A is also from -0.3 to Vcc+0.3 V (which is 3.6V), just like DS90CR482.  For both devices this is Abs Max, not operating spec.  

    The 2.5V common mode is not compliant with spec.  They need to reduce it. Please note that this is not a limitation of our devices; this is LVDS standard. Devices from other manufacturers also follow that standard.

  • 0 in reply to Yaser Ibrahim
    Prodigy 10 points
    Hi team,
    As what you've said above ,Four LVDSs have different values of voltage, is it true?
    The datasheet shows Vcm is 1.2V. Compared with picture above ,how to explain that?
    Wish your reply ,thanks.
  • 0 in reply to user5294365
    TI__Genius 10250 points
    Hello,

    The picture above also shows that Vcm at transmitter is 1.2V, just like the datasheet. At the receiver there could be ground shift causing Vcm at the receiver to be different.

    Regards,
    Yaser