AM4372: Pull-up/down resistor

Hello Goto,

Thank you for the query.

Data sheet reference

DC Electrical Characteristics (continued)

All other LVCMOS pins (VDDSHVx = 1.8 V; x=1–11)

All other LVCMOS pins (VDDSHVx = 3.3 V; x=1–11)

The customer needs to consider the combined worst case leakage current associated with all devices connected to a signal to understand what value external pull is required to ensure the resulting potential remains at a valid high or low logic level when not actively driven to a high or low logic level.  They need to be careful and not use a resistor value that is too low, such that the output buffer driving the signal is not able to achieve a valid logic state.  They may also need to consider noise sources that could induce a potential on a signal and make sure they apply an appropriate external pull that is able to hold a valid logic level when exposed to the noise source. 

Regards,

Sreenivasa

Hello Goto,

The below tips can be used as reference:

https://www.ti.com/lit/ds/symlink/omap-l138.pdf

4.3 Pullup/Pulldown Resistors

Tips for choosing an external pullup/pulldown resistor:
• Consider the total amount of current that may pass through the pullup or pulldown resistor. Make sure
to include the leakage currents of all the devices connected to the net, as well as any internal pullup or
pulldown resistors.
• Decide a target value for the net. For a pulldown resistor, this should be below the lowest VIL level of
all inputs connected to the net. For a pullup resistor, this should be above the highest VIH level of all
inputs on the net. A reasonable choice would be to target the VOL or VOH levels for the logic family of
the limiting device; which, by definition, have margin to the VIL and VIH levels.
• Select a pullup/pulldown resistor with the largest possible value; but, which can still ensure that the net
will reach the target pulled value when maximum current from all devices on the net is flowing through
the resistor. The current to be considered includes leakage current plus, any other internal and
external pullup/pulldown resistors on the net.
• For bidirectional nets, there is an additional consideration which sets a lower limit on the resistance
value of the external resistor. Verify that the resistance is small enough that the weakest output buffer
can drive the net to the opposite logic level (including margin).
• Remember to include tolerances when selecting the resistor value.
• For pullup resistors, also remember to include tolerances on the IO supply rail.
• For most systems, a 1-kΩ resistor can be used to oppose the IPU/IPD while meeting the above
criteria. Users should confirm this resistor value is correct for their specific application.
• For most systems, a 20-kΩ resistor can be used to compliment the IPU/IPD on the boot and
configuration pins while meeting the above criteria. Users should confirm this resistor value is correct
for their specific application.
• For more detailed information on input current (II
), and the low-/high-level input voltages (VIL and VIH)
for the device, see Section 5.3, Recommended Operating Conditions.
• For the internal pullup/pulldown resistors for all device pins, see the peripheral/system-specific terminal
functions table.

Regards,

Sreenivasa