AN2727 Freescale Semiconductor / Motorola, AN2727 Datasheet - Page 29

• Manufacturer Part Number: AN2727
• Description: Designing Hardware for the HCS12 D-Family
• Manufacturer: Freescale Semiconductor / Motorola

When driving high impedance loads such as logic devices the voltage dropped across the output RDSON
will be low, and the VOH and VOL levels will be much closer to the appropriate supply rail voltages.
I/O Injection Currents
All digital I/O pins are internally connected to VSSX/VDDX, VSSR/VDDR, or VSSA/VDDA via protection
diodes. Taking an input pin above VDD5 or below VSS by greater than a diode drop will cause current to
flow to or from the internal device supply rails, via the protection diodes. This is known as “current
injection” and is valid as long as the application limits the injected current to within specified limits.
Continuous (IICS)
Up to
Device Total (IICP)
The sum of the injected currents on all pins = Σ
Instantaneous Maximum (ID, IDL)
Short duration injection current maximum
guaranteed but the device will not be damaged. The IICP limit must be respected.
Keep current injection on any individual input less than IICS (2.5 mA) and the total device current injection
less than IICP (25 mA). If any pin transient exceeds IICS, MCU functionality is not be guaranteed but, as
long as the individual pin current and the total device current remains less than 25 mA, the device will not
be damaged.
Analog Input Considerations
In addition to the above constraints, current injection on ATD inputs may cause additional error in
conversions of adjacent pins. A portion of the injected current will also be picked up by the adjacent
Freescale Semiconductor
±
2.5 mA per pin. MCU functionality is not guaranteed if any single pin exceeds this value.
The power supply must maintain regulation within operating VDD or VDDX
range during instantaneous and operating maximum current conditions. If
positive injection current (Vin > VDD or Vin > VDDX) is greater than IDD or
IDDX, the injection current may flow out of VDD/VDDX and could result in
external power supply going out of regulation. Make sure that the external
VDD/VDDX load will shunt current greater than maximum injection current.
This will be the greatest risk when the MCU is not consuming power.
Examples are: when no system clock is present, as in STOP mode; when
the clock rate is very low, which would reduce overall power consumption.
Designing Hardware for the HCS12 D-Family, Rev. 0
±
25 mA (on any single pin). MCU functionality is not
⏐
IICP
NOTE
⏐
. Maximum = 25 mA.
I/O Injection Currents
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