NXP Semiconductors MPC560xP, Design Manual

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Table 22. ADC conversion characteristics
Symbol Parameter Conditions Value Unit
Min Typ Max
I
INJ
Input current
injection Current
injection on one
ADC input,
different from
the converted
one. Remains
within TUE
specification -5 5 mA
TUE Total
unadjusted
error without
current injection - -2.5 - 3 LSB
TUE Total
unadjusted
error with
current injection - -3 - 3 LSB
NOTE
In case overload condition can not be avoided, injection current specification (I
INJPAD
,
I
INJSUM
, I
INJ
) can be applied which limits the current at internal clamp by using an
external series resistor, however, current injection should be minimized because it causes
degradation of ADC accuracy.
9.3 Handling unused pins
In some applications, not all pins of the device may be needed. Good CMOS handling practices state that all unused pins
should be tied off and not left floating. On the MCU, unused digital pins can be left open in the target system. Almost all pins
have internal pull devices (either pullup or pulldown devices
2
). For unused digital pins, it is recommended that software
disable both the input buffers and the output buffers of the pads in the Pad Control Register for the ball. In addition, the weak
pulldown device should be enabled. This keeps the pad in a safe state under all conditions.
For analog pins, it is recommended that they be pulled down to VSSA (the analog return path to the MCU).
2. Technically, these devices are not resistors. They are active weak transistors that pull the input either up or down.
Pin Overview
Hardware Design Guide, Rev. 0, 2012
24 Freescale Semiconductor, Inc.