Allegro 3213 example circuit help

Hi - I’m going to purchase an Allegro 3213 hall effect sensor to experiment with detecting model trains on a layout. I’m looking at the example circuit diagram from:

https://www.allegromicro.com/Products/Magnetic-Digital-Position-Sensor-ICs/Micropower-Switches-Latches/~/media/Files/Datasheets/A3213-4-Datasheet.ashx

I’ve got a couple of questions.

What is the 10pF capacitor for on Vout ? The sensor output is HIGH when no magnetic field is detected and the MOSFET ties it LOW in the presence of a magnetic field.

Secondly, the data sheet says it can sink 1mA on Vout. What sort of current will a micro controller draw when reading that output ?

To the second question, the leakage current of an ATmega328p (as in UNO) input pin (without pullup resistor) is about 1 micro amp.

Ok. Thanks for that.

I’m still trying to get this to work after a long break. The Hall effect sensor has an open drain output capable of sinking only 1mA. I would like to illuminate an LED as it triggers so 1mA will not be enough to do this as well provide the sink current for the MCU (3D printer end stop input).

Should I be using a PNP transistor to provide the current sink when it’s base is driven low or should I be looking at a small FET ? I have spent a day reading about sizing the transistor base resistor to get the transistor to saturation to act as a switch but I’m still confused. I’m not sure how to go looking for a PNP transistor that will saturate at 5v while drawing 1mA max through its base resistor.

How would you drive an LED from an open collector output from this Hall effect sensor ?