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SN74LVC541A: Value of Icc vs input Frequency

Daisuke Higa
Genius 3515 points
Part Number: SN74LVC541A

Hi support team.

I received some inquiries regarding Fig 5 Icc vs frequency at P12 in datasheet from my customer.

1. Is it  MHz as the unit of frequency on the horizontal axis?

2. Is the value of Icc for 1ch or the sum of all channels in Fig5?

3. Could you tell me the circuit or/and conditions as you measured?

    Conditions are temperature/Load/...

My customer would like to estimate Icc on the three conditions below.

Case 1 : Using All channel is 5MHz.

Case 2 : Using 4 channels are 5MHz and other 4 channels are 10MHz 

Case3 :  Using 4 channels are 10MHz and other 4 channels are DC inputs. 

I appreciate if you provide some information.

Let me know if you have any question.

Thank you for your cooperation.

Best regards,
Higa

  • 0 in reply to Clemens Ladisch
    Genius 3515 points

    Hello Ladisch-san

    Thank you for yopur reply.

    However, your answer is not what I want to know.
    I would like to know the measurement conditions in Fig. 5.
    What are the values of RL and CL?
    How many channels have you measured?

    In my calculation result, the value of Icc does not match FIG5 under the following conditions.

    VCC = 3.3V
    Nsw = 4ch
    CL = 30pF
    RL = 20kohm (calculated from datasheet)
    Cpd = 33pF (from datasheet)
    fi = fo = 10MHz
    D = 0.5
    Voh = 2.4V (from datasheet)
    Ptotal = 0.027692W
    Icc = 8.4mA

    In the graph of FIG5, Icc is approximately 55mA at 10MHz.
    There is a big difference between my calculation result and the value in the graph.
    I think it's because RL and CL are different, but I don't know what's causing it.

    Best regards,

    Higa

  • 0 in reply to Daisuke Higa
    TI__Guru* 96591 points

    Hello Higa-san,

    I have verified that your calculations are correct.

    I don't have data on how this plot was created, but it looks like it was calculated rather than measured (the lines are perfectly straight), so it's likely that there was just an error in the calculation. I would guess that the engineer that did the calculation was using the datasheet measurement specs of 50pF and 500 ohms.

    I will add this datasheet to our errata list to fix. The fix will be to remove this graphic.