AN2434 Freescale Semiconductor / Motorola, AN2434 Datasheet - Page 7

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

Injection Current
When the applied voltage or an input pin rises above V
According to the device electrical specification for the 9S12DP256, injected currents should be limited to
±2.5 mA for any single pin. Injection currents above this specification can cause current to flow in the
substrate of the device which can cause increased voltage differential and can affect the accuracy of
analog conversions, and in the most extreme case, it can cause damage to the device. A variable power
supply was used to raise the voltage applied to an input pin while the internal pullup is disabled. The
current flow into the input pin was recorded and is summarized in
Figure 4
Subjecting a device input pin to current above the maximum limit in the device specification can result in
damage to the part. At an injected current of approximately 700 mA, current abruptly drops to 0, indicating
an internal failure. (If the input is current-limited, the voltage into the current-limiting resistor can be raised
above 11 V without a failure.) The failure is caused by an electrical over-stress (EOS) or by melting of the
bond wire which connects the I/O pin to the internal silicon die. EOS can cause the bond wire or metal
traces on the die to fuse open. Failure analysis can determine the actual cause of failure by a microscopic
examination.
For more information on the effects of electrical over-stress and electrostatic discharge (ESD) damage,
please refer to
Freescale Semiconductor
shows the effect of a semiconductor diode clamp to V
Appendix A
6.2
5.8
5.6
5.4
5.2
4.8
6
5
0
Figure 4. Port A0 — Injection Current versus Voltage
and
MC9S12DP256, 25°C, Port A0, V
Appendix B
1000
Input/Output (I/O) Pin Drivers, Rev. 0
at the end of this application note.
CURRENT (µA)
2000
DD
, current can be injected into the input pin.
DD
DD
.
Figure
= 5 V
3000
4.
4000
Injection Current
7