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SN74LVC2G34: Short Circuit Current

Part Number: SN74LVC2G34

Customer is using SN74LVC2G34DBVR to drive an external LED via via 49.9ohm resistor (sourcing current).  The customer is concerned with short circuit on the external LED wiring damaging the SN74LVC2G34DBVR due to current above the 50 mA absolute max.

What is the risk if they decide to leave the circuit as is?

Does TI offer an alternative device that can support 65 mA short circuit current?

Please advise.


  • The risk is that the device will be damaged (short circuit or open circuit or one after the other).

    Two outputs in parallel would allow 100 mA.

  • Hey Mark,

    Clemens is correct. I just wanted to add that there are a few options in this scenario:

    (1) Increase the resistor value to 75 ohms -- most LEDs will still produce a very good amount of light even at half their rated current, and this would be the cheapest/easiest solution to prevent any damage. At 71 ohms (75 - 5%) and 3.3V, the output short circuit current is limited to 46.5mA, which is within the device's capabilities.

    (2) Use one SN74LVC2G34 per LED and parallel both channels. The device can support up to 100 mA total current, and you can parallel channels within the same device (don't try it with multiple devices though, as this can introduce timing differences).

    (3) I put this last since it is least likely to be useful - but it's still worth mentioning.  You might be able to increase the LED supply voltage to 5V -- in this scenario, 1.7V additional falls across the limiting resistor, which allows for a larger resistor value at the same current output, and thus ends up with a short-circuit safe output. Assuming 5V and 2.3V Vf at 20mA, the resistor needs to be 135 ohms, which results in short circuit current of 37 mA.

  • Thanks for the detailed response.  My recommendation was #1, increase the resistor value and see what effect it has on LED brightness.

    Appreciate the quick reply.