About internal pullup/pulldown resistor value of AM3517

Internal pull-up/pull-down resistors are implemented with week transistors.  As the voltage present on the I/O pin varies the relative gate voltage to this week transistor changes which will cause the effective pull-up/pull-down resistance to change.  Therefore, internal resistors do not have a linear response like external resistors.  That is part of the reason you see internal pull-up/pull-down resistors specified as having a wide range of resistance.  The wide range of resistance also provides margin for process variation.

I’m still trying to determine the typical drive strength for the internal pull-up and pull-down resistors for these pins.  I hope to have a better answer in a few days. 

I have normally seen this type of I/O cell specify a typical value of 100uA.

Regards,

Paul

I just realized the word “weak” was spelled incorrectly.  The post should have read:

Internal pull-up/pull-down resistors are implemented with weak transistors.  As the voltage present on the I/O pin varies the relative gate voltage to this weak transistor changes which will cause the effective pull-up/pull-down resistance to change.  Therefore, internal resistors do not have a linear response like external resistors.  That is part of the reason you see internal pull-up/pull-down resistors specified as having a wide range of resistance.  The wide range of resistance also provides margin for process variation.

I’m still trying to determine the typical drive strength for the internal pull-up and pull-down resistors for these pins.  I hope to have a better answer in a few days. 

I have normally seen this type of I/O cell specify a typical value of 100uA.

Regards,

Paul

I found the following information in some internal documentation.  This indicates the typical value for both is 150uA.  However, the pull-up may range from 70uA to 330uA and the pull-down may range from 75uA to 270uA.

6. I _I(PU) is the on-state current through a pullup. I _I(PD) is the on-state current through a pulldown. Single values in the nominal column represent the typical current with all conditions at their nominal recommended values. The ranges shown in the nominal column represent the typical variation of current with stated conditions at the values shown and unstated conditions varying over their full recommended ranges. Conditions may include voltage, temperature, and process.

Regards,

Paul

RY said:

 - I think that I can calculate the resistor value as R=V/I.
   Is it correct?

Yes, this is the equation to use for calculating the effective resistance.

RY said:

 - The AM3517 can operate two types of voltage level(3.3V or 1.8V).
   When I calculate the resistor value,
   which voltage level(3.3V or 1.8V) can I use?

Use the voltage level that you are going to implement in the system.  If you are going to apply 3.3V to the voltage supply rail servicing these I/Os, then 3.3V should be used in your calculations.  Similarly, if you are going to apply 1.8V to the voltage supply rail, then use 1.8V in your calculations.