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ISO1228: Abnormal LED light

Zoey Wu
Expert 5855 points
Part Number: ISO1228

Tool/software:

hi team,

my customer is using ISO1228 and they found that the LED works normal under sink mode.But when in source mode , the LED will stay light whatever the input.

Could u kindly give some advise? thanks!

  • 0
    TI__Mastermind 29375 points

    Hello Zoey, 

    Thank you for reaching out. In order for the LED to light up in both sink and source mode there needs to be two LEDs per LEDx pin. This allows the LED current to flow in both modes. Please see our [FAQ] How to Enable Sink/Source Mode without Terminal/Component Changes? for an example of how to enable Sink/Source mode. We will also have an EVM featuring this topology released next month

    Please provide a schematic of the customer solution if further review is needed. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Expert 5855 points

    hi Andrew,

    their schematic is as below and the Rilim=0Ω，Rthr=1kΩ，Rpar=16kΩ. But when INX is no input, the LED will also light. The LED they are using now will conduct with only 200uA .Is there any possibility that this problem is caused by the current when wire break detection? 

    And is the function of Rsuge to prevent the surge in hot swap? when the Rsuge =1k, INX=0, the LED will be lighter. Do u know what is the reason?

  • 0 in reply to Zoey Wu
    TI__Mastermind 29375 points

    Hello Zoey, 

    I would need to see the customer's schematic to confirm the LED direction and provide possible reasons why it is lighting up in source modes. Currently, I think that you are right and current from the wire break detection is causing the LED to light and that the LED is in the sink mode direction. I cannot confirm this without the customer schematic. 

    The EVM I mentioned in my last post is now released. ISO1228EVM Evaluation board | TI.com. The sink/source mode EVM is a good reference on how to structure a board to support both operation modes. 

    The use a surge-proof resistor at Rsurge allows the ISO1228 to can protect against surges of without the need of an external TVS diode in Sink Mode (see 7.3.1 Surge Protection for more details). 

    Best,
    Andrew