no voltage drop across pullup resistor

[sudheervemana]

Hi all,

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.

Thanks in advance,
Sudheervemana.

 

[The Real Andy]

Hi all,

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.

Ohms law. Do the math and i think you may find a voltage drop, a very small
one though. You will need to refer to the manufacturers data sheet to see
how much current is drawn through the resistor from the device pin.

 

[Robert Baer]

Hi all,

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.

Thanks in advance,
Sudheervemana.

There are various reasons for this interpretation: 1) there is no
current thru the resistor, 2) the drop is too small for determination on
the scale you are using (not enough sensitivity), or 3) you are not
making the measurement correctly and/or the meter is altering the
circuit too much.

Re-read what i said in response to one of your other queries.

If you are really serious about learning electronics, i have a number
of Navy ane other electronicbooks i could send to you.

 

[dB]

[email protected] (sudheervemana) wrote

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.

The impedance at the pin to which the pull-ip is connected will be
much higher than the value of the pull-up. So, any drop across it
will be very small.

 

[Rene Tschaggelar]

Hi all,

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.

Especially CMOS parts have no DC input current, except perhaps some
femto to pico Amps.

Rene

 

[John Fields]

Hi all,

In many of the applications i have seen that the function
of a pullup resitor is to attain a desired value across a pin.can any
one explain me why the voltage is not getting dropped across the pull
up resistor.