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TCA6424A LED Connection

Raja Ashutosh Kedia
Intellectual 430 points
Other Parts Discussed in Thread: TCA6424A

Hi,

The datasheet at Page-26 mentions, "The LED acts as a diode so, when the LED is off, the I/O VIN is about 1.2 V less than VCC." As per my understanding, the port act as an output pin in this case and hence voltage at the pin should be either VCCP or GND irrespective of state of LED. When it is VCCP, LED will be OFF and when it is GND, LED will turn on. Can you please clarify the same?

Regard,

Raja

  • 0
    TI__Genius 16510 points
    Raja,

    In many cases, the user may wish to set the port to an input to make it high-Z. BY doing this, they can guarantee that no current flows. In many cases, the LED could be driven by a voltage higher than VCC, and in this case, setting the output high may still result in current flowing through the diode. For this reason, many customers will set the port to either output low, or to input. When an input, the pin voltage should be held at VCC to prevent shoot through current. By using a resistor in parallel with the LED, you can ensure the pin is pulled up to VCC when not being used.
  • 0 in reply to Jonathan Valdez
    Intellectual 430 points

    Hi Jonathan,

    In our use case, we have connected anode terminal of LED to 3.3V supply and cathode terminal of LED to TCA6424A (whose VCCP is 3.3V) via a series resistor. The port of TCA6424A is set as output always. It is high when LED is required to be turned off and low when LED is required to be turned on. No current flows when LED is off and 10mA current flows (TCA6424A acts as sink) when LED is On. Do you see any issues with this scheme? I have attached a reference connection diagram for your reference.

  • 0 in reply to Raja Ashutosh Kedia
    TI__Genius 16510 points

    Raja,

    If VCC is 3.3V for the IC and LED, then you are OK setting the output to high to turn the LED off instead of to input. You're fine doing what you want.