# Current into level shifter IC from microcontroller

I am trying to do a power assessment of a microcontroller (TMS320F28379D, datasheet link: https://www.ti.com/lit/ds/sprs880o/sprs880o.pdf?ts=1702312460730)

From the below datasheet, is $$\ 4mA \$$ the maximum current that the pins of the microcontroller configured as output can supply?

Now, the output pins of the microcontroller is connected to a level-shifter IC's $$\ 3.3V \$$ side, for shifting to $$\ 5V \$$ (SN74LVC4245A, datasheet link: https://www.ti.com/lit/ds/symlink/sn74lvc4245a.pdf?ts=1702310500407).

In the table below, I am unable to find the current that the input pins of the level shifter IC will take.

My understanding is that even though the microcontroller's input pins can supply a current of $$\ 4 mA \$$, the actual current will depend on the output stage, which in this case is the level shifter IC.

Am I looking at the wrong data, or is my understanding wrong?

• Pay attention to note (3). Commented Dec 12, 2023 at 13:46
• @winny The microcontroller's output pins are connected to the 3.3V side of the level shifter IC. I will try to update the question with a schematic. Commented Dec 12, 2023 at 13:58
• @Hearth So, does this mean that whatever output pin from the microcontroller connected to the 3.3V side of the level shifter IC will add an additional 0.5mA to the supply current? I apologize if my understanding is wrong as I am new to reading datasheets and understanding these ICs. Commented Dec 12, 2023 at 14:04
• @curious_direwolf Sorry, I meant note (2). That's close to but not exactly what note (3) means, but that's not the note I meant to call your attention to anyway. Commented Dec 12, 2023 at 14:06

The input pins take a maximum of either +/-5uA (control inputs) or +/-50uA (I/O pins). Typical is probably in the nA or less at room temperature.

Of course the pins also have a small amount of capacitance (as will the traces used to connect the two) so there is a brief pulse of current whenever the levels change.

Supply current is another matter.

From the schematic, you are using it in the recommended configuration with CMOS input levels so:

Icca should be < 80uA

Iccb should be < 50uA

None of which is supplied by the MCU pins, of course.

• How to go about computing the supply current from the datasheets for this arrangement? Commented Dec 12, 2023 at 14:08
• That's another question and I would like to see the simplified schematic including all supplies. Commented Dec 12, 2023 at 14:10
• I have added the schematic. Commented Dec 12, 2023 at 14:38
• See edit above. Commented Dec 12, 2023 at 14:51
• So the supply current for B port is <50 uA, and the input pins (3.3 V side) of the level-shifter will only take 5uA, and the microcontroller outputs also will supply the same 5uA, is that correct? Commented Dec 12, 2023 at 14:55

My understanding is that even though the microcontroller's input pins can supply a current of 4mA, the actual current will depend on the output stage, which in this case is the level shifter IC. Am I looking at the wrong data, or is my understanding wrong?

The level shifter provides buffered outputs so, the input current into port A/B of the level shifter is not dependent on the output current from port B/A.

Input pins take up to +/- 5 μA.

• Thank you. I have updated the question with a schematic. How can the supply current from the 3.3 V supply of the level shifter IC be computed? Commented Dec 12, 2023 at 14:39