# what will happen when providing two pull up resistors in same line

If two pull ups given in a situation one pull is 4.7 K-ohm and other pull up is 10 k-ohm was given to open-drain pin then what will happen? Imagine the open-drain was connecting to an IO pin of an external MCU

In open drain pin's device datasheet it was mentioned that open drain pin as input will handle max of 10 uA. In that case will that 1 mA damage the open drain pin ? actually there will be current division right (or) will all current enterily flows towards the open-drain pin ?

• Ah, let me see. If the output IC is a switching MOSFET, and when switched on, then Vsd ~= 0V (Rds9on ~= 0) , so I output ~= Vsupply/Rpull-up. On the other hand Input depends on input resistance Rinput, Ic ~= 0V / Rinput. ~= 0A. If fet switch of off. Then Iinput = Vsupply/ Rinput. Just thinking aloud, nothing proofread. Commented Oct 10, 2020 at 9:45

You'll have a pull-up of 4k7 || 10k = 3k2.

The open drain pin will have to handle a maximum current of V / R = 3.3 / 3k2 = 1 mA.

In open drain pin's device datasheet it was mentioned that open drain pin as input will handle max of 10 uA.

This sounds as though you are mis-reading it. It doesn't "handle" a current but may source or draw up to 10 μA. That means that the pull-up resistor would have to source 10 μA into the input to keep it high. That's not an issue.

In that case will that 1 mA damage the open drain pin?

The open drain pin is on your "Output IC". Check the datsheet. It can probably sink 50 mA.

... actually there will be current division right (or) will all current entirely flows towards the open-drain pin ?

When the line is high the pull-up will supply 10 μA to the input.

When the line is low the pull-up will supply 1 mA to the open-drain transistor.

For almost all practical purposes you can ignore the input current for CMOS devices because it is so low for steady-state conditions. At high frequencies the situation changes because you have to charge and discharge the input capacitance.

• Thanks for reply...Edited question again and asked one more question with picture in main question section itself Commented Oct 10, 2020 at 9:39
• See the update. Commented Oct 10, 2020 at 9:52