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ISO1212: Surge protection for ISO1212/ ISO1228

Anicia Yu
Prodigy 40 points

Part Number: ISO1212
Other Parts Discussed in Thread: ISO1228

Hi,

I'm using the ISO1228 configured for source inputs and the ISO1212 configured for sink inputs in a 28VD aerospace application.

While reviewing the datasheets, I noticed the recommendation to add a TVS diode for surge protection. I would like to clarify how this recommendation relates to the optional input filter capacitors.

  1. For the ISO1228, does the recommended TVS diode replace the CFIL capacitor, or should both be populated when surge protection is required?
  2. For the ISO1212, does the recommended TVS diode replace the CIN capacitor, or should both be used together?
  3. If a TVS diode is already installed at the connector on every I/O line, is an additional TVS diode recommended near the ISO1228/ISO1212 devices, or is the connector mounted TVS sufficient? 
  • 0
    TI__Genius 16900 points

    Hi Anicia,

    Thanks for reaching out. Please find my inputs below:

    1. For ISO1228, both are required — the TVS diode does not replace CFIL.
      1. TVS diode is a must in source type inputs for surge protection. CFIL between AVCC-AVSS provides local decoupling to the IC and must be of 1nF value which is required for the proper functioning of the current limit function
    2. For ISO1212, both may be used together — the TVS diode supplements CIN rather than replacing it.
      1. The CIN capacitor (10 nF to 330 nF) provides filtering and contributes to prevent overshoot beyond 60V during transitions and also meeting surge requirements at lower levels.
      2. For higher voltage levels of surge tests or for faster systems that cannot use a large value for CIN, TVS diodes or varistors can be used.
    3. Ideally if the TVS diode is able to clamp the voltage the at 28V all the INx and VCC pins then yes, the TVS at connector pin good enough.
      1. But in order to have redundancy - considering aerospace application - additional TVS near to the device, for avoiding any overshoot risk, is always recommended for added safety.

    Regards
    Varun

  • 0
    Prodigy 40 points

    Hi Varun,

    I am using the recommended component values for a Type 3 system, including CFIL = 1 nF. Since the TVS diode is used in addition to the input capacitor (CFIL/CIN) rather than replacing it, I will include both components in my design.

    I also have a question regarding the LED feature. If I would like to use the input status indication shown in the datasheets, do I need to add external LEDs?

  • 0 in reply to Anicia Yu
    TI__Genius 16900 points

    Hi Anicia,

    Anicia Yu said:
    I am using the recommended component values for a Type 3 system, including CFIL = 1 nF. Since the TVS diode is used in addition to the input capacitor (CFIL/CIN) rather than replacing it, I will include both components in my design.

    Sure, sounds good.

    Anicia Yu said:
    I also have a question regarding the LED feature. If I would like to use the input status indication shown in the datasheets, do I need to add external LEDs?

    Yes, external LEDs on the respective LEDx pins for ISO1228.

    For having LEDs on ISO1212 ISO1212 - Refer section "8.2.1.2.7 Status LEDs" in the datasheet.

    Regards
    Varun