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DS90UB927Q-Q1: VDDIO in mipi csi and 927

Amelie Zheng
Genius 10865 points
Part Number: DS90UB927Q-Q1

Hi Team,

My customer design DS90UB927Q-Q1.

The LVDS of CPU is powered by 1.8V VDDIO in SOC. So the Common mode voltage of LVDS in CPU output is 1.2V. 

Could customer use 3.3V as VDDIO to power 927? Does it have risk for CPU and SER in the VDDIO are not the same?

Or the VDDIO of 927 need to keep the same as VDDIO of SOC(1.8V)?

  • 0
    TI__Mastermind 25955 points

    Hi Amelie,

    Common mode voltage for the LVDS pins is nominal 1.2 V in either, as specified in the device datasheet.

    Are there any perceived benefits to the design by using 3.3 V for the 927 when the uC is at 1.8 V?

    Keeping the I/O at the same voltage may simplify interconnect for pins such as PDB and like thresholds, for example, with I2C.

    Sincerely,
    Bryan Kahler

  • 0 in reply to Bryan Kahler
    TI__Genius 10865 points

    Hi Bryan,

    My customer also feel confused about the VCM. Why the max value of VCM is 2.4V? In which application, will VCM become 2.4V?

  • 0 in reply to Amelie Zheng
    TI__Mastermind 25955 points

    Hi Amelie,

    It will remain nominally at 1.2 V.  This is the LVDS interface and not the LVCMOS I/O.

    If you are seeing different results, please share a scope shot.

    Sincerely,
    Bryan Kahler

  • 0 in reply to Bryan Kahler
    TI__Genius 10865 points

    Hi Bryan,

    If the LVDS output signal from MPU to 927 is VCM=1.2V, and 927's VDDIO=1.8V. I could know that no problem.

    But if the LVDS output signal from MPU to 927 is VCM=1.2V, but 927's VDDIO=3.3V.

    What is the actual VCM voltage on the LVDS from MPU to 927?

    Is it still 1.2V?

    Or because VDDIO of 927 is 3.3V, so VCM from 927 is higher than 1.2V. Will it make the LVDS signal come back from 927(VCM >1.2V) to MPU(VCM=1.2V)?

    Or actually VDDIO only decide the GPIO voltage(such as I2C/I2S), not decide the LVDS VCM?

  • 0 in reply to Amelie Zheng
    TI__Guru** 103215 points

    Amelie,

    Bryan has already explained several times. VCM for the LVDS interface is independent of VDDIO. No matter what configuration the device is used in, the VCM will be typically 1.2V but could range from 0-2.4V. 

    VDDIO controls the other I/O voltages like GPIO, I2C, I2S as you say 

    Best Regards,

    Casey