CM1223 Datasheet, PDF (9/19 Pages) California Micro Devices Corp – Industry First Low Capacitance ESD Protection Arrays w/Backdrive Protection

CM1223
Backdrive Protection
Backdrive protection is needed to block against backdrive current flowing from a high potential voltage node
toward a lower potential voltage node through the interface cable.
For example, consider a DVD player connected to a TV via an HDMI interface. If the DVD player is switched off
and the TV is left on, there is a possibility of reverse current flow back into the main power supply rail of the
DVD player. Typically, the DVD's power supply has some form of associated bulk supply capacitance, and it is
possible over time to charge that bulk supply capacitance to some intermediate level.
If that level rises above the power-on-reset (POR) voltage level of some of the integrated circuits, the DVD
player may not reset properly when the DVD player is turned back on. This is largely because all CMOS logic
exhibits a very high impedance on the power rail node even when "off".
To avoid this situation, the CM1223 with integrated backdrive protection diode was designed to block backdrive
current, guaranteeing no more than 5µA on any I/O pin when the I/O pin voltage is greater than the CM1223
supply voltage.
Application Information
Design Considerations
To realize the maximum protection against ESD pulses, care must be taken in the PCB layout to minimize
parasitic series inductances on the Supply/Ground rails as well as the signal trace segments between the signal
input (typically a connector) and the ESD protection device. Application of Positive ESD Pulse between Input
Channel and Ground illustrates an example of a positive 8kV ESD pulse striking an input channel. The 8kV ESD
current pulse will divert along the path as indicated in Application of Positive ESD Pulse between Input Channel
and Ground, through the D1 diode and the Zener diode back to the ground rail.
An ESD current pulse can rise from zero to its peak value in a very short time. For example, a level 4 contact
discharge per the IEC61000-4-2 standard results in a current pulse that rises from zero to 30 Amps in 1ns. The
CM1223 has a fast response time of less than 1ns and low clamp voltage to handle this pulse scenario.
Similarly for negative ESD pulses, parasitic series inductance from the V_N pin to the ground rail will lead to
drastically increased negative voltage on the line being protected.
The CM1223 also has an integrated backdrive diode between V_P and V_N to prevent backdrive current flow from
the powered sources.
As a general rule, the ESD Protection Array should be located as close as possible to the point of entry of
expected electrostatic discharges.
Additional Information
See also California Micro Devices Application Note AP209, “Design Considerations for ESD Protection”, in the
Applications section at www.cmd.com.
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