AN2434 Freescale Semiconductor / Motorola, AN2434 Datasheet - Page 5

• Manufacturer Part Number: AN2434
• Description: Input/Output (I/O) Pin Drivers
• Manufacturer: Freescale Semiconductor / Motorola

Device Damage
additional input must be made available later in the design process. Pins that may be used as input/output
should be terminated individually to permit maximum flexibility if they are needed later in the design
process. Pins that are configurable as outputs should never be connected to other such pins, because
failure to correctly configure the pins could result in greatly increased power dissipation and may possibly
result in damage to the device.
A pin-by-pin review of every MCU design should be performed to ensure that all unused pins are
terminated correctly. This should specifically account for package variations where not all signal lines are
accessible on pins, such as on reduced pin count packages. These hidden signals must still be treated
as unused pins and configured appropriately to reduce power consumption and noise.
Device Damage
Please note that exceeding the device absolute electrical specifications will result in damage to the MCU.
The information contained in this application note is provided to show what happens when pins are
subjected to loads beyond those in the electrical specification.
Metal migration is caused when the device is heated, even within a small local area, due to excessive
current flows. This allows metal atoms to move and causes thinning of traces or shorts to adjacent
circuitry within the part. Thinning of traces leads to higher trace resistance, which in turn raises the
temperature and continues the process.
Over time, enough metal can be eroded to cause an open circuit or a resistive connection resulting in
reduced reliability. Metal layers are designed for a maximum current density, and they have to be
operated below those levels to ensure reliability. When the metal and silicon traces are designed,
assumptions are made (for example, they are designed for an average current—not peak). A 50% duty
cycle is assumed for current driven on a given pad; therefore, average current is assumed to be no higher
than 50% of peak current.
Input/Output (I/O) Pin Drivers, Rev. 0
Freescale Semiconductor
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