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SN65HVS882: System Protection for Input Module

Ahmed Noeman
Expert 3520 points
Part Number: SN65HVS882

In Figure 21 of the datasheet, an application circuit demonstrating the system protection for the SN65HVS882 device is shown. for the input terminals, it depends barely on the 1.2kW resistor.

My question is:

- what is the maximum protection this circuit offers in case of Continuos voltage (mis-wiring) and Surge event?

- in case of 1kV surge event, we will have ~1A for about 20 uS, where this current will flow after capacitor charging? there is no information in the datasheet about the maximum current in case of ESD event and for how long it can flow. only the normal operation 5mA limit.

- if the device is relying on internal diode to channel this current to the VCC, can this diode withstand such current?

- in case of Continuos voltage of say 30V, there will be 25mA of current through the 1.2kW resistor while normal current limit is 5mA. what is happening in this case? increase of pin voltage and turn on of the ESD structures leading again to a condition like above with less current?

Those questions are related to a Customer opportunity which  we are working on right now.

Thanks in advance!

  • 0
    TI__Expert 3520 points
    Another related question is : is a minimum current of 2mA is required to detect logic 1? can I detect logic 1 for much lower current limit, say 100 uA? according to Rlim spec, this limit is possible. but shall this work for detection? I'd like to use it in non standard application for detecting certain levels.
  • 0
    TI__Mastermind 25705 points
    Ahmed,

    In HVS882 there is one 15kV HBM ESD rating diode to GND for each IPx pin. In general, it's about 0.7A/kV peak current for HBM event. Can you double check peak current during your surge event? It looks a little too low for 1kV surge (IEC 61000-4-5 www.ti.com/.../slva711.pdf) If the current level is around amp level, I think the diode should be able to take it.

    You can also refer to this thread for the input characteristic of the pin. (e2e.ti.com/.../15559) Basically it shows 300kOhm until the ESD cell trip point. After that, I/V slope depends on the characteristic of ESD cell.

    If input current limit is set to 5mA by Rlim, the voltage across 1.2kOhm Rin will be 6V. Thus the voltage on IPx will be 30-6=24V.

    From the datasheet, it looks possible to set current limit to 100uA by a Rlim around 0.9MOhm (90V/100uA). It should work for detection if you make input voltage Vin-on threshold works for you as well.

    Please let me know if you have any further question.