✔ Calculation For Pull Up Resistor

Calculation For Pull Up Resistor

- April 28, 2018

And the current will be the maximum current sunk by the logic pins. In bipolar logic families which operate at operating at 5v the typical pull up resistor value is 1 5 kw.

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An output an output voltage v out of 18 v is used as an example.

Calculation for pull up resistor. For switch and resistive sensor applications the typical pull up resistor value is 1 10 kw. Supply voltage 24v sink current 16ma r vi 24016 1500w now we need information on the load to determine the maximum pull up resistor. Also resistor array schematics.

So theoretically if this bus has the absolute maximum amount of capacitance on it this bus should use at least 177 k ohm pull up resistors down to 171 ohm resistors if their maximum low drive strength is 135 ma each during sclsda low. If you do need resistor pull ups next determine if you should use an individual resistor or a resistor array. Tie the input directly to the rail without a resistor although in ultra low power designs this is not a good practise up to 100 kohm or possibly more should work fine.

Now that ipull up has been calculated the maximum value for rpull up is found by using equation 2. Example cmos values used 1 check i ih or maybe just i i for same devices input high current on the data sheet. A rule of thumb is to use a resistor that is at least 10 times smaller than the value of the input pin impedance.

So if we assume a voltage drop of only one volt 10v across the resistor giving double the input voltage at 4 volts a quick calculation would give us a single pull up resistor value of 50kw. These pull ups would draw 33v 177 k 186 ma each when scl sda is low. So r pull up v supply v hmin i sink.

Calculate the pull up resistor value. If its a pull updown for a not high speed high impedance digital logic input then virtually any resistor from 0 ohms ie. In case of the pull up resistor the v will be the source voltage minimum voltage accepted as high.

Here is how to calculate the minimum pull up resistor. Reducing the resistive value further will produce a smaller voltage drop but increase the current.