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CDCUN1208LP: Power consumption

Part Number: CDCUN1208LP

I would like to check if I understood the data seet right.

My use case is as follows:

I- LVDS input (IN1P and IN1N);

II- 8 LVDS outputs

III- VDD and VDDOx = 1.8V

IVa - Input frequency 5MHz, square

IVb - Input frequency 160MHz in bursts (67% active, 33% idle)

Assumptions below based on Table 14 of the data sheet.

1- IDEV is the core (i.e. VDD) current and it does not depend on fout and fin. The table assumes input is LVCMOS (ITTP open) but LVDS input should not impact IDEV significantly. 

2- ILVDS is the per output current (i.e. half the VDDOx total current), not dependent on fout and fin.

So I used IDEV = 80mA and ILVDS (total) = 8 * 9mA = 72mA. Therefore total device current consumption is 152mA. I assume the current does not vary significantly between static (i.e. no fin) and normal operation as stated in IVa and IVb above.

So my first question is if the assumptions above are correct. If not, how do I determine the current consumption?

My second question is what is the typical current consumption of this device?

  • Hi Elder,

    The 80mA should be the max current consumption when all outputs are enabled according to the datasheet, because the "OE" column is high.

    I'm afraid the typical current consumption is not provided in the datasheet.

    Regards,
    Hao
  • Hello, Hao.

    Thank you for your answer.

    It occurred to me that IDEV could be the total current but ICORE is 26mA (all outputs off) and per data sheet, all outputs on sum up 72mA so it seems unlikely the core would require only 8mA under such a condition. Our measurements suggest 156mA is closer to the value. The measurements were taken with the board that uses six units but the board has other circuits and we are not able to make isolated measurements.

    Regarding the typical values, I asked because the data sheet does not mention them. Yet it would be useful to know the values. I suppose the maximum values were taken from many measurements so I guess there should be an average value that reflects the typical (expected) values or a design spec.

    Again, thank you for your support.

    Elder.

  • Hello Hao,

    IDEV-LVDS, the max. current the device consumes in LVDS mode is 80 mA at 100 MHz.
    ILVDS, the max. current consumed by each LVDS driver is 8 mA -> total 72 mA for 8 LVDS outputs at 100 MHz.
    Each VDDOx supplies 2 outputs, so with differential LVDS output ILVDS is per output.
    When all 8 LVDS outputs are on I would expect to measure around 152 mA of current at 100 MHz.
  • Vibhu Vanjari said:
    Hello Hao,


    IDEV-LVDS, the max. current the device consumes in LVDS mode is 80 mA at 100 MHz.
    ILVDS, the max. current consumed by each LVDS driver is 8 mA -> total 72 mA for 8 LVDS outputs at 100 MHz.
    Each VDDOx supplies 2 outputs, so with differential LVDS output ILVDS is per output.
    When all 8 LVDS outputs are on I would expect to measure around 152 mA of current at 100 MHz.

    So my understanding regarding how the total current is correct.

    It would be useful to know the frequency dependency and typical values (even if a ballpark figure would be useful).

  • Hello Elder,

    I've placed an order for the EVM of the part to take a bench measurement on. Please let me know what frequency/frequencies you are interested in and I will follow-up next week.

  • Hello, Vibhu.

    The frequencies in my design are 5MHz and 160MHz.

    Thank you very much for your support.

    Best Regards,

    Elder.

  • Hello, Vibhu.

    Have you been able to take the measurements?

    Elder.

  • Hello Elder,

    My previous responses were not accurate. I've taken measurements on the bench for 160 MHz and 10 MHz clocks (not 5 MHz).
    When all output drivers are enabled (LVDS, 1.8V VDD and 1.8 VDDOx) I see 78 mA and 56 mA at 160 MHz and 10 MHz respectively.
    When all output drivers are disabled (LVDS, 1.8V VDD and 1.8 VDDOx) I see 37 mA and 16 mA at 160 MHz and 10 MHz respectively.

    In the table IDEV-LVDS includes all current/power consumed by the device.

  • Hello, Vibhu,

    Thank you very much.

    Elder.