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LM2903-Q1: Comparator Common-mode input-voltage range

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Part Number: LM2903-Q1

Dear sir or madam

We are using LM2903VQPWRQ1, and in datasheet of LM2903-Q1,  Common-mode input-voltage range stays below Vcc-2V.

With a note : "The upper end of the common mode voltage range is VCC+ − 1.5 V for the inverting input (−), and the non-inverting input (+) can exceed the VCC level; the comparator provides a proper output state."

Does it mean the inverting input (−) must be lower than Vcc-2V for a proper output?

In our design, Vcc is 5V, V+ is2.8V, V- is 3.9V. Is it OK for a proper output?

Thanks in advance.

Regards,

Ruipeng

  • Hello Ruipeng,

    The Vcc-1.5 is for room temperature and above. If you will be going cold, you should use Vcc-2V.

    So I will be conservative and use Vcc-2V. So the maximum input voltage for a +5V supply should be +3V.

    The +IN is within the limit (2.8V). The -IN is outside the limit (even at Vcc-1.5).

    So only one input is within the specified range. The output will be correct, but it may not be meeting other datasheet specifications such as offset, bias current and prop delay.

    Please see the following appnote for further explanation:

    Application Design Guidelines for LM339/LM393/TL331 Family Comparators

    Regards,

    Paul Grohe

    TI Comparators (CMPS) Applications Group

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