• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 15 subscribers
  • Views 194 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ISO1228: LEDx to GND in Sink mode & Clarification the equations

Mohammad Zinati
Prodigy 10 points
Part Number: ISO1228

Tool/software:

Hello

1. I want to use ISO1228 and i don't need the visual indication & wants to LEDx direct to the ground but i read in section 7.3.2

"The LEDx pins can be connected directly to GND in sink mode provided wire-break detection is not used and V24V in source mode."

so if i connect LEDx direct to GND in sink mode, i lost the wire-break detection. Am i right? i really interested how happen is this? i can't figure it out from Block diagram Fig 7.1.

if just voltage drop on led is concerned, can i replace it with a resistor with same voltage drop once input is high?

2. the second question is about the equations in datasheet and the fixed number in that. where is the origin of this number? how is calculated?

for example in equation for wire break detection RIWB = (VINX -2V) /IWB - RTHR. what is the reference of 2v? is it voltage drop on LED and if i connect direct LED to GND this eqation is not valid?

or other equation on section 8.2.3.1.1 

VIH (typical) = 6.0 V + RTHR x IL (typical) (2)
VIL (typical) = 5.0 V + RTHR x IL (typical) (3)
VIH (max) = 6.4 V + RTHR x IL (max) (4)
VIL (min) = 4.7 V + RTHR x IL (min) (5)

 how calculated the numbers of 6, 5, 6.4, 4.7?

Thanks

  • 0
    TI__Mastermind 18925 points

    Hello Mohommad, 

    Thank you for reaching out.

    1. You are correct that the wire break is only available in source mode and if the LEDx pins are connected to LEDs or similar diodes. Let me confirm with the team to see if I can tell you specifics. 
    2. These numbers are each constant that are a result of the internal circuitry of the device.  

    Best,
    Andrew

  • 0 in reply to Andrew Jackiw
    Prodigy 10 points

    Hello Andrew

    Thanks for your response

    I had meant, the wire break is only available in Sink mode.  Is my understanding correct?

    Andrew Jackiw said:
    the wire break is only available in source mode

    I would appreciate it greatly if you could share more specific detail.

    Thanks,

    Best regards,

    Mohammad

  • 0 in reply to Mohammad Zinati
    TI__Guru 53085 points

    Hi Mohammad,

    Andrew is currently looking into your questions and is going to come back with answers later this week. Thank you for your patience.


    Regards,
    Koteshwar Rao

  • +1 in reply to Koteshwar Rao
    TI__Mastermind 18925 points

    Hello Mohammad, 

    Sorry to keep you waiting. Here is the clarification from the team. 

    Mohammad Zinati said:
    so if i connect LEDx direct to GND in sink mode, i lost the wire-break detection. Am i right? i really interested how happen is this? i can't figure it out from Block diagram Fig 7.1.

    Wire break works only in sink mode. In source mode, wire break detect is not available because there is no way to distinguish between and "ON" and a wire break.

    You can choose to use a diode if an LED is not needed. However, 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

    The equation assumes a VLED of ~2V. The equation is "RIWB = (VINX - V_DiodeDrop) /IWB - RTHR," if you are not using a 2V LED/Diode.

    Mohammad Zinati said:

    VIH (typical) = 6.0 V + RTHR x IL (typical) (2)
    VIL (typical) = 5.0 V + RTHR x IL (typical) (3)
    VIH (max) = 6.4 V + RTHR x IL (max) (4)
    VIL (min) = 4.7 V + RTHR x IL (min) (5)

     how calculated the numbers of 6, 5, 6.4, 4.7?

    These numbers are the worst-case threshold values in the device. Rthr is needed to meet the type 1,2 or 3 DI inputs standard, however the equation is still valid if RTHR = 0.

    Best,
    Andrew 

  • 0 in reply to Andrew Jackiw
    Prodigy 10 points

    Thanks for your helpful reply.