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LM2903-Q1: input protection

Umberto Frangi
Expert 4045 points
Part Number: LM2903-Q1

Hi,

 I would like to know your opinion about an input  circuit protection.

At -IN there is connected a diode with anode to GND, so the input can go down to -0.7V, that is below the datasheet margin of -0.3V.

But to limit the input current there is a 10KOhm resistor.

Do you think this is enough to avoid any device failure?

And do you think the device is not showing any wrong behavior in such condition, like wrong switching?
Thanks

Umberto

  • 0
    TI__Mastermind 49916 points

    Hello Umberto,

    The LM2903-Q1 does NOT have internal input protection, and voltages lower than the ground pin can cause malfunctions or damage.

    Use a Schottky diode instead, like a BAV199 type, which has a lower forward voltage and allow the external diode take the brunt of the current and reduce the negative excursion.

    You want to limit the current to as little as possible. For the LM290x family, I recommend less than 1mA into the pin since there is no protection.

    The external diode is taking the brunt of the current, but the lower the current, the lower the forward voltage. So it is best to limit the current st as little as possible.

    10k ohm sounds reasonable, but depends on the expected negative excursion. The recommended resistor value would be R = Vovervoltage / 1mA.