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TL431: TL431

Jani Isoo
Intellectual 1930 points
Part Number: TL431

looking at implementing a load dump protection circuit – based around the TL431 (actually based on your app note –SNVA681A–March 2015).

I’ve got a couple of questions:

 

Looking at Fig 6 – C1 will act as a speed up cap causing U1 to turn on as soon as the voltage starts to rise – Can I remove this as it prevents setting the voltage correctly ?

We need to withstand a voltage of 80V – this will put a voltage on Vref of about 6V – is this safe ?

Whilst the circuit is clamping the cathode voltage will be below Vref – again is this safe ?

  • 0
    TI__Expert 3835 points
    Hi Jani,

    The feed-forward cap (C1) helps improve stability and the transient of the load dump. If this is preventing you from setting the correct voltage then it can be removed or reduced. The trade-off would be a slower response and perhaps instability from removing the zero from the frequency response.

    The REF pin does not have a voltage rating, but current rating. The high voltage is fine since there are resistor dividers that will limit the current of the REF pin. Having the cathode voltage below the REF voltage is also okay. This application uses the TL431 in an open-loop configuration which is defined in our datasheet.

    Regards,
    Ethan