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ISO1228: LEDs lighting up when input disconnected in source mode

Brayden Box
Prodigy 10 points

Part Number: ISO1228

I have followed the reference design in the ISO1228 datasheet for source/sink mode with the back-to-back LEDs for each channel on the LEDx pins.  What I have found, is that in sink mode, the LEDs work properly.  However, in source mode, the LEDs are quite bright even when the inputs are disconnected.  They do get brighter when an input is active, but why are they on at all?  Does the chip have high internal leakage, or could this be the wire break detection current?  The LEDs I am using are APHB1608LVBDZGKC.  Thanks

  • 0
    TI__Guru* 76132 points

    Brayden,

    If possible, can you share a schematic of the circuit? I want to make sure I understand the power scheme and the direction the LEDs are facing. Based on your description, it could be the wire break detection current, but that may mean that the LEDs are facing the wrong polar direction given they are in source mode. 

    If you don't feel comfortable posting a schematic to the public E2E forum, you can email it directly to me at e-hackett@ti.com.

    Regards,

    Eric Hackett