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LM2901: LM2901

ITZIK MIZRAHI
Prodigy 210 points
Part Number: LM2901

hi,

i wanted to ask about the output value status, when i put on the output pull-up (3.3V through 10kohm resistor), the +VCC of the device is 24V and the -VCC of the device is 0V.

for my understanding:

  • if the + input larger then - input, then the output will be 3.3V
  • if the - input larger then + input, then the output will be 0V

but, what happened if no pull-up placed on the output?

thanks,

  • 0
    TI__Guru 55126 points
    Hello Itzik,

    You are correct. The output will go "high" to the pull-up resistor termination voltage (Vt), regardless of comparator (V+) supply voltage.

    The "output" is essentially a single pole switch from the output pin to GND. When the switch is open, the output is pulled-up by the resistor. When the switch closes (-IN > +IN), the output switch turns on (conducts) and shorts the resistor to GND (0V).

    If no pullup resistor is placed on the output, the output will be essentially zero, as the output has no capability to go "high". It may float a few dozen mV above 0 due to base leakages, but that is very weak and overcome by any loading.