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LM2903B-Q1: Input short to battery

Shinji Tsuji
Genius 14349 points
Part Number: LM2903B-Q1
Other Parts Discussed in Thread: LM2903B, LM339, LM393LV

Tool/software:

Hi team,

We are using LM2903B-Q1 as a non- inverting comparator with the hysteresis.

Can we apply the battery voltage at the non-inverting pin while the supply voltage is 3.3V?   Are there any reliability issues?

What will be the output voltage if the non- inverting input voltage is higher than the reference voltage of 2.5V.

I am presuming that op-amp output is saturated to the supply voltage of 3.3V. Please confirm?

regards,

  • 0
    TI__Guru 63396 points

    Hello Shinji,

    The LM2903B inputs can go up to 38V without damage. We would recommend a series resistance to limit any current should there be a fault (~1k or so) when directly connected to a battery or a supply.

    What is the battery voltage?

    "What will be the output voltage if the non- inverting input voltage is higher than the reference voltage of 2.5V."

    The valid input voltage range (Vcc-2V). 

    At 2.5V input on 3.3V supply, the maximum input voltage over temperature is 3.3 - 2 = 1.3V max. So you are already violating the 1.3V input maximum at 2.5V. 

    Under your conditions, both inputs would be above the input limit, causing the "both inputs above" behavior.

    For the current "B" (Ji3) silicon, the output would be high. But that may change in a year or two.

    This is all covered in the LM339 family application note. Please see sections 6.2, 6.4 and 6.7:

     Application Design Guidelines for LM339, LM393, TL331 Family Comparators

    At 2.5V, you could be floating between the "Feature" behavior and the "Both Inputs Above" behavior, so the output condition could change over temperature.

    "I am presuming that op-amp output is saturated to the supply voltage of 3.3V. Please confirm?"

    Not quite sure what is being asked (the output can only sink current), but if you are asking if the output will be "high", then the last paragraph above answers that (could be high or low depending on temperature).

    If the battery voltage is below 5.5V, then the LM393LV could be used. It has a R-R "fail-safe" input that could tolerate the battery voltage, even with the power off (as long as it is below 5.5V).

  • 0 in reply to Paul Grohe
    TI__Genius 14349 points

    Hi Paul-san,

    Does any simulation model that I can simulate the behavior beyond the input voltage range?

    I see below notes in TINA TI model on TI.com. 

    * Model Notes:
    * Modeled parameters:
    * Supply Voltage Ranges
    * Input Voltage Range
    * Supply Current
    * Input Bias Currents
    * Typical Offset Voltage
    * Propagation Delay
    * Error Conditions:
    * If the input goes beyond the recommended input voltage range, the output will float to mid supply
    * If the supplies goes beyond the recommended supply voltage ranges, the output will float to mid supply
    * The real device will NOT do this.

    Regards,

  • 0 in reply to Shinji Tsuji
    TI__Guru 63396 points

    Hello Shinji,

    We do not want to encourage out-of-datasheet behavior. This is why we flag it in the model.

    The behavior also depends on which version of the die you get.

    Please see the LM339 family appnote, sections 6.4, 6.7 and 6.8:

    Application Design Guidelines for LM339, LM393, TL331 Family Comparators