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ULN2003A: Should this part be used for connecting to a 3.3V mcu?

Part Number: ULN2003A

Tool/software:

Someone answered this before in the forum (They said yes, this works great for 3.3V), but I wonder if a TI engineer could look into this?  If we are driving 24V relays with this device, and we want to use an mcu with 3.3V CMOS (Not TTL - like the ULN2003A datasheet says it's compatible with), how will this device work.

I'm trying to see if it's ok for my mcu to have enough current to power multiple ons.  When I look at the datasheet for Iin, it says Vi is 3.85V, and they do not go lower than this.  What is the Ii(on) when I'm driving it with 3.3V?  Wouldn't it be better just using a TPL7407, it says 3.3V and 5V.  I'm concerned that there may be issues with this part overheating or drawing more power than mcu can provide.  I'm just looking for justification on switching to a new part, when we have been using the ULN2003A in older products and don't want to add another part to our library and purchases, but now upgrading our mcu to 3.3V, and want to make a better decision rather than avoiding to add a part to our current library.

  • Hi Jim,

    Yes, either ULN2003A or TPL7407(L or LA) will work with 3.3V. Please see the below image for the required on-state input voltage. The input current at 3.85V is 1.35mA max for ULN - for TPL, the input current is very small because it is buffered.

    Below is the diagram for each channel of ULN, so the input current is just (VIN - 2VBE) / 2.7k. So your input current at 3.85V will be less, maybe around 1mA max.

    Thanks,

    Patrick