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SN74AVC2T245: Level Shifter static power consumption question

Jacob Verheyen
Prodigy 20 points

Part Number: SN74AVC2T245

Hi,

I'm trying to calculate the static power consumption of the SN74AVC2T245. According to application note SCEA030B (Voltage Translation Between 3.3-V, 2.5-V, 1.8-V, and 1.5-V Logic Standards), total static power consumption is given by the following formula.

PTOTAL = (ICCA)(VCCA) + (ICCB)(VCCB) + (IOL)(VOL)(NL) + (IOH)(VCC – VOH)(NH)


The I_oh variable represents the high-level output current. I have two questions related to this.

  1. For the SN74AVC2T245, I_oh is negative. Why is this? Is current flowing into the device?
  2. When calculating static power dissipation, this can lead me to calculate a negative value for power consumption in some scenarios. Should I instead be using the absolute value of I_oh instead of the negative value when performing my calculations?

Thanks,
Jacob

  • 0
    TI__Guru* 97666 points
    Hi Jacob,
    You may notice that I_oh is negative in all of our datasheets - this is a convention we have set -- current into a device is positive, current out of a device is negative. For the sake of power calculations, you probably shouldn't be using that number though -- you need to determine the output current for _your_ system. Do you have a resistive load? Most likely there's much less output current than the rated I_OH or I_OL specification.