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Thread: Resistance of a XMC4500-Pin against GND for dimensioning a voltage divider

  1. #1
    New Member New Member b2kbutt is on a distinguished road
    Join Date
    Oct 2018

    Resistance of a XMC4500-Pin against GND for dimensioning a voltage divider


    I'm triing to control a BLDC-Motor with a XMC4500 Relax Lite Kit.
    Sadly the motors hall sensors work with a 5V-Logic, so i have to convert their signal to 3,3V so the XMC won't get damaged
    One way how to acomplish this would be using linear voltage regulators but I wondered, if could do it the quick and dirty way and use a voltage divider built with resistors.
    To find the correct dimension of the resistors, i looked up the datasheet for a resistance value of a pin configured to input to ground(?) but could not find any information.
    Is my way of thougt completly wrong or are there people who tried to acomplish a similar goal

    Best regards,

  2. #2
    Intermediate Intermediate
    Infineon Employee
    Infineon Employee
    Eric is on a distinguished road
    Join Date
    Mar 2013
    Hi b2,

    usually Hall switches connect Q output to GND when they detect a magnetic field.
    E.g. Figure 3 Functional Block Diagram TLE4965-5M

    This means you can connect Q with a pull up resistor to 3.3V or you can use the XMC pull up resistor.
    The power supply remains 5V or you choose a 3,3-5V switch like TLE4965-5M.

    Best regards
    The views expressed here are my personal opinions, have not been reviewed or authorized by Infineon and do not necessarily represent the views of Infineon.

  3. #3
    Beginner Beginner Alberto-g is on a distinguished road
    Join Date
    Oct 2017
    I guess he is referring to linear output Hall current sensor.
    Input ADC inpedance should not be so important for the divider ratio, LEM sensors can source milliamps IIRC.
    Problems come from the fact that ADC needs to be driven by a very low impedance source, so you should put a relatively high capacitor parallel connected to ADC input.
    Doing so you would have a low pass filter that lowers precision of fast changing signal measurement.
    I would definitely put an op amp there. ADC of micros are already so bad, there is no need to make them worse.

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