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# SN74AHCT541: Supply current and dissipation calculation

Part Number: SN74AHCT541

Hello,

I see that Figure 5 on the datasheet shows 270mA @50MHz 3.3V operation. ((270e-3/8)/50e6)/3.3 = 204pF per channel. Why is the current in that figure this high? I see in section 7.9 the power dissipation capacitance per buffer as 33pF. So I'd expect 8*33pF*3.3V*50MHz = 43mA total supply current instead of 270mA.

Kind regards,

Zeki

• Hi Zeki,

Can you please link to the datasheet you are referencing? The datasheet for SN74AHCT541 ( https://www.ti.com/lit/ds/symlink/sn74ahct541.pdf ) doesn't include a figure as you describe.

• Hi Emrys,

My bad :), I now realized that the component I was looking at was SN74LVC541ARGYR. Should I create a new question or would you be able to help me in this page?

Kind regards,

Zeki

• Hey Zeki,

You forgot a square in your power consumption calculations - 8*33pF*(3.3V^2)*50MHz = 144 mA -- which still isn't quite as high as what is shown.

Figure 5 shows a calculated power consumption estimate for the LVC family in general. This is useful to show generally how power relates to voltage and frequency in the device, but shouldn't be used as a replacement for calculation.

I can see how it's confusing since it's listed as a typical curve for the application section -- I'll mark this for deletion in the next datasheet revision.

• Hi Emrys,

I think you've calculated the power by multiplying again with the voltage, so it would be 144mW but 43mA @3.3V. In any case, I understand that the figure is supposed to be qualitative and not quantitative. Thanks for the help!

Kind regards,

Zeki

• Hey Zeki,

Yeah - my mistake. Sorry about that.