Input/Output Pins
MPC5746R Hardware Design Guide, Rev. 1
NXP Semiconductors 27
Figure 15. Example Weak pull up/down configuration.
Following example describes how to calculate a suitable pull-up resistor value based on data sheet
specifications.
Example:
External resistor R=4.7 kΩ
120 uA max weak pull up current as specified in the data sheet when VDD_HV_IO >= 4.5 V.
Voltage drop (V
IL
)= 4.7 kΩ x 120 μA = 0.56 V
The voltage above pin is less than V
IL
max= 0.35x4.5 V = 1.575 V at V
DD
=4.5 V
Therefore R=4.7 kΩ is suitable.
The same principal applies for internal weak pull down scenarios.
Device for
internal weak
pull up
PAD
(pin)
V
IL
V
DD_HV_IO
4.5 – 5.0V
V
IL
must be in the
spec range
-0.3V ~0.35*V
DD
IIWPUI = 120µA
(Max current drain out of
MCU)
External resistor
R
to determine
Lo level
GND
Voltage drop
=
external pull resistance x
max internal weak pull current
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