I want to check my Li-ion Charger( Microchip MCP73833 ) status with nRF52832.

So i will connect Stat 1,2 and PG to nRF But MCP73833 have an open-drain output

If i connect pins to nRF without Pull-UP resistor and use nRF's internal pull-up is it ok ?

  • \$\begingroup\$ Those internal pullups are about 10kOhm on NRF52x, so they should work unless there is lots of electromagnetic noise present. \$\endgroup\$
    – Turbo J
    Oct 17, 2017 at 12:25

2 Answers 2


It seems you want to sense the state of a open drain output with a microcontroller.

Open drain outputs only actively drive low. For the logic high state, they go to high impedance instead of actively driving high. Something else needs to make the line go high when the open drain output is in the high impedance state. Otherwise, the line will stay low once it is driven low.

The usual solution is to connect a resistor between the line and the positive supply. That's such a common thing that it has its own name of "pullup resistor". 10 kΩ is a good value for most ordinary cases. I go into detail about the value to use for a pullup resistor HERE.

Check the datasheet of your microcontroller. Many micros have internal passive pullups that can be enabled on some of their pins. If you are using such a pin, then you don't need any external part at all. Just enable the internal pullup in the micro.

  • \$\begingroup\$ i've got it ! i have tried one and that works thank you for your reply :) \$\endgroup\$
    – Bongjin
    Oct 28, 2017 at 7:42

As long as there is some pull-up resistor somewhere on the line, it will work.


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