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AM37x pullup / pulldown sizing

AndMan
Intellectual 335 points

Hi,

I am in the process of sizing / determining the need for the pullup and pulldown resistors on the IO around the AM37x. For other digital device's I've typically calculated the required size of the resistor based off of the voltage drop which would occur across the pullup / pulldown due to total maximum leakage current, then ensuring that VIL or VIH would still met when factoring in that voltage drop.

In the case of the AM37x, the pullup / pulldown values are spec'd in terms of drive strength (datasheet sec 2.3), and the input leakage current only appears to be specified for the I2C inputs. What is the proper way to determine the need for / size of a pull resistor when specified this way? 

Thanks - AM

  • 0
    TI__Expert 4745 points

    AndMan,

    As you may know, the AM 3715 has internal pullups and pulldowns which are deemed sufficient unless you have a load out there that needs to be pulled high or low.

    In those instances the size might be determined by the external device requirements and the supplier's DS definition / need for pullups and pulldowns.  

    If you just want to terminate unused, please refer to the datasheet and put the same pull up or pulldown as suggested. 

    If there are specific pins you are concerned about, please provide a list and we can evaluate the needs case by case.

  • 0 in reply to DaveB123
    TI__Guru 64470 points

    In addition to Dave's comments, the AM37xx datasheet does provide information on the active current through the internal pullup and pulldowns.  Section 2.3 eludes to this in Note 11 talking about the PULL U/D TYPE field.  The pullup/pulldown drive strength is equal to min=50uA, typ=100uA and max=250uA, except for noted signals.