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Original question:

ISO1228: 4 pcs ISO1228 in daisy chain

ISO1228: Use the Resistor to replace LED

Chen Alex1
Expert 2725 points
Part Number: ISO1228

Tool/software:

HI Sir

Due to space issue, we need to remove the led & Resistor replace it

have any issue?

  • 0
    TI__Mastermind 18955 points

    Hello Alex,

    In order to maintain the wire break feature of the ISO1228, you can choose to use a diode if an LED is not needed. The device needs some consistent voltage drop for the wire detect feature to work. A resistor cannot be used because it will not have constant voltage drop. Any diode of voltage higher than 0.8V can be used for wire break. 

    Also, please review "Figure 8-2. Sinking Type Digital Inputs with ISO1228". The cathode of the diode/LED should be connected to AVSS and not in parallel with the input signal.

    Best,
    Andrew 

  • 0 in reply to Andrew Jackiw
    Expert 2725 points

    hi Sir

    if i use the IN4148 to replace LED, iso1228 can work correct?

    thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 18955 points

    Hello Alex,

    The IN4148 should work to replace the LED since it has VF = 1V (assuming IF=100mA). Please let me know the updated schematic. 

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    Expert 2725 points

    hi Andrew

    Due to board space issue, we need to remove the all in4148 , after remove the in4148, if have problem?

  • 0 in reply to Chen Alex1
    TI__Mastermind 18955 points

    Hi Alex, 

    The diodes are typically needed for full operation of the device. Certain features may be unavailable, however let me check with the team to see if there is a way to operate with less diodes or no diodes. 

  • 0 in reply to Andrew Jackiw
    TI__Mastermind 18955 points

    Hello Alex,

    ISO1228 can operate without LED/diode in both sink and source mode but the wire break detection will not be available. “The LEDx pins can be connected directly to GND in sink mode provided wire-break detection is not used and V24V in source mode.” (7.3.2 Field Side LED Indication).

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    Expert 2725 points

    hi Andrew

    could you describe it detail? thanks

    The LEDx pins can be connected directly to GND in sink mode provided wire-break detection is not used and V24V in source mode.” (7.3.2 Field Side LED Indication)

     the pin is mean The LED

    1. short the pin to Ground, what happen?
    2. The pin pull high to 24v ,what happen?
    3. floating the pin,what happen?thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 18955 points

    Hi Alex, 

    Good questions. Please allow me some extra time to answer them. I am checking with the team on a few items. 

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    Expert 2725 points

    hi

    Could i reduce the resistor space from 0805 down to 0603  Size?

    thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 18955 points

    Hello Alex, 

    You can use the size needed for your application. However, please keep in mind that the smaller resistors will need to be rated for the correct surge and power rating that your application requires. 

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    TI__Mastermind 18955 points

    Hello Alex, 

    Thank you for your patience. To answer your questions, see below: 

    • In sink mode, LEDx pins can be connected to GND. A diode is needed for wire break detection to work. Wire break detection will not be available if the LEDx pin is shorted. 
    • In source mode, the LEDx pins can be connected to AVCC (wire break detection is not available in source mode). 
    1. short the pin to Ground, what happen?
      1. In Sink mode, no issue. The device will operate. 
      2. In Source mode, this is an invalid condition the device will not operate as expected.
    2. The pin pulled high to 24v, what happen?
      1. In Sink mode, this is an invalid condition the device will not operate as expected.
      2. In Source mode, no issue. The device will operate. 
    3. floating the pin, what happen? 
      1. Not a valid function. Device will not operate as expected.

    Best,
    Andrew