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LM2903: LM2903

Part Number: LM2903


Need to understand

Query 1

1:We are using LM2903-Q1 comparator in our design.


Design considerations.

We are using it as window comparator.(Two Comparators COMP 1 an COMP 2)

 Input voltage will from VIN =  0-5V.

Upper Threshold 3.665V ( at COMP 1)

Lower Threshold 1.335V ( at COMP 2)

Vcc = 5V

Open drain Supply also 5V.

Temperature consideration 85 deg C

We need to understand the effect of Parameter Common mode Input Voltage range VICR on output voltage.


We have kept our upper threshold as 3.665V.

We need to know if we are providing input voltage VIN > 3V.

Whether it will be accepted and it will provide output based on pull up Vcc,when upper threshold is crossed

or output will be clipped above 3V not providing output greater than Vcc-2 i.e. 3V.


Input voltage cannot be accepted greater than Vcc-2 i.e 3V.

As per datasheet VICR is  0 to Vcc-2V for full scale temperature range.

Please provide the solution for it.


Siddharth Sangam

  • Hi Siddharth,

    you should never exceed the allowed common mode input voltage range, otherwise strange things can happen, like output phase reversal, degradation of timing characteristics and latch-up. The usual way to prevent the input signal from exceeding the allowed common mode input voltage range is the use of a resitive voltage divider at the input.

  • Can there be another possibility such that

    if I use Vcc = 12V or 15V and output is open drain supply connected to 5V.

    As per VICR output will not be greater than Vcc-2 (12-2=10V) max range.  

    So, my circuit will  toggle above threshold voltage (VTH upper threshold = 3.665V) as Vcc is kept at much higher voltage.

    And output will be not affected, output phase reversal, degradation of timing characteristics and latch-up will not happen.

    Is the solution??? 

    Or to use Rail to rail output comparator.

    Siddharth Sangam

  • Hi Siddharth,

    yes, of course, you can do that.