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MSP430G2153: Impedance of GPIOs

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Part Number: MSP430G2153

e2e, 

I'm trying to find the input and output impedance of the GPIOs of the MSP430G2153.  I want to create a model for my SPI signal but need to know how to calculate the source and load resistance from the datasheet. 

From the datasheet below it looks like the source impedance can be calculated by the 0.3 V drop with 6mA of current which would be about 50 ohms. 

From the load impedance the max leakage would be 3V / 50nA with load resistance molded as 60M ohms. 

 What would be a situation I would use the  internal pull down resistor to have the load impedance at 20k ohms? 

Thank you,

Adam 

  • Hi, Torma,

    For source resistance calculation, your method is ok to get draft value. The resistance value is nonlinear. To get accurate value, you can refer to figures 6 to figure 9 (Typical Characteristics, Outputs). For example, in Figure 9, there is voltage drop of 0.3v with 10mA at 3v-2.7v case. So we can get the 30 ohm source resistance for this case.
    For the load resistance calculation, your method is also ok to get draft value. But please notice the 50nA is just maximum value. So the 60M ohm is the minimum value across the process, temperature and voltage variations.
    Internal pullup and pulldown resistor is for input case. For output case, the internal pullup and pulldown resistor should be disabled by reset the PxREN register. Otherwise, the output will be abnormal.

    Regards,
    Lixin
  • In reply to Lixin Chen1:

    Hi, Torma,

    I haven't heart from you for long time. I think it is resolved for you. If you have further questions, please reply on this thread directly.

    Thanks,
    Lixin

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