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Original question:

[FAQ] How to use a high side switch (HSS) to implement one fail all fail in a multi-module automotive LED rear light system...

New technique for one fail-all fail in LED rear lights

Kevin Kirby
Prodigy 20 points

So, if we assume that, in figure 2, pcb1 = a fender lamp and pcb2 = a trunk lamp then the situation you describe works for a failure of a fender lamp. However, how would this work for a failure of a trunk lamp where the fender lamp can legally remain functioning (e.g. tail or stop functions)?

Kind regards,

Kevin Kirby

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    TI__Genius 10652 points

    Kevin,

    Sorry for the delay in response.

    The design goal you described is not a fail-one fail-all scenario.

    From what i understand, Fender lamp fails, trunk lamp being forced off is OK, however, if the trunk lamp goes out, it is still legal for fender lamp to continue so you want that case to keep fender lamp(s) on.

    below is a snippet from that FAQ

    1. LED failure in PCB1. When a PCB1 LED failure occurs, the LED channels on PCB1 will be disabled and the LED driver Fault pin goes low. This turns off the HSS, which results in the turning off LEDs in PCB2. That is, failures in PCB1 will also turn off all LEDs in the lamp.
    2. LED failure in PCB2: When a PCB2 LED failure occurs, the LED driver will turn off the LEDs in PCB2. The current consumption of PCB2 reduces and the HSS in PCB1 detects this as an open load. The HSS fault pin goes low and disables the LED drivers on PCB1. This then turns off the LEDs in PCB1. Thus, failures in PCB2 will turn of all LEDs in the lamp.

    Basically if we cut this "trace", if Trunk LEDs fail, TPS1H200A will show fault, but that fault will not pull EN low of the PCB1 LED driver (tails). But the Tails failing will still keep the trunk LEDS off.

    But then that EN signal would need to have to driven from a controller or pulled high.

    Other option is to allow Fault of the LED drivers from each PCB1 and PCB2 to feedback to controller. Controller negotiates the fail-one fail all only for certain cases just as you mentioned.

    Or some simple discrete logic can accomplish this.

    Hopefully this helps, please let us know if you have additional questions. But if this answers your question, could you press the green button to let us know.

    Best

    Dimitri