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LM2903-Q1 Absolute Max Rating of Input

Expert 5565 points

Replies: 4

Views: 1099

Hello,

I understand that the absolute Max rating of LM2903-Q1's input voltage is -0.3 V on the negative voltage side. However, I'm wondering whether -1 V is tolerable if the current that flows through the pin (either IN+ or IN-) is 0.1 mA or smaller. In the system, -1 V could be applied to IN- pin, but the current flow will be as low as 0.1 mA.

Best regards,
Shinichi Yokota

  • Hello Yokota-san,

    Our product expert for this device is currently out for the rest of the week for the Thanksgiving Holiday here in the US.
    My initial estimate would be that this should be ok, but I cannot guarantee it. Might you be able to await further guidance from the product expert next week?

    Best,
    Michael

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  • Hello Shinichi,

    Yes. If the current is limited to low currents (<1mA or less) damage can be avoided. Typically a resistor in series with the input is used to limit the current.

    However, the LM2903 does not have ESD diodes, so there is not a defined current path for the negative voltages and the current flows through the internal devices an into the die substrate. The current paths are uncontrolled, so even a small current flowing in the wrong place can cause issues (failures, latch-up, etc).

    If voltages below ground are expected, we recommend adding a Schottky clamp diode to ground to provide a controlled current path and shunt the current around the input. The forward voltage of a Schottky diode is less than the substrate "diode", so the Schottky will start conducting before the substrate and conduct the current around the substrate.

    Regards,

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

  • In reply to Paul Grohe:

    Do we offer a Vcc > 12V dual open-drain comparator that will handle the case where a negative voltage may be applied to Vin (through a limiting resistor)? Would the TLC372-EP work with the < 1mA limited current mentioned above?
  • In reply to Steve Widener:

    Hello Steve,

    None of the devices in our comparator portfolio will handle input voltages below their negative supply pin.

    Most will accept a voltage slightly below V-, down to -0.3V is generally acceptable.

    Most of the newer devices have ESD protection on the inputs that clamp to the supplies. But the older devices, like the LM2903 family, do not have ESD diodes, and negative voltages will reverse bias the internal die junctions and do "bad things".

    If negative voltage is expected, a external resistor and external clamp diode should be used. Schottky's are recommended since they have a lower forward voltage (0.3 to 0.4V) and will conduct earlier than the internal junctions (0.6 to 0.8V) and take the brunt of the current.

    Keep in mind that comparators do not need absolute voltage levels. They are just comparing voltages. If you have negative voltages, it is possible to use level-shifting (pull-up) resistor networks to bring the trip points up to legal positive values.

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

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