© 2004 California Micro Devices Corp. All rights reserved.

6

430 N. McCarthy Blvd., Milpitas, CA 95035-5112

L Tel: 408.263.3214

L Fax: 408.263.7846 L www.calmicro.com

01/09/04

CM1209

Application Information

Design Considerations

In order 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 segment

between the signal input (typically a connector) and the

ESD protection device. Refer to Figure 4, which illus-

trates an example of a positive ESD pulse striking an

input channel. The parasitic series inductance back to

the positive supply voltage.

An ESD current pulse can rise from zero to its peak

value in a very short time. As an example, a level 4

contact discharge per the IEC61000-4-2 standard

results in a current pulse that rises from zero to 30

Similarly for negative ESD pulses, parasitic series

to drastically increased negative voltage on the line

being protected.

The CM1209 has an integrated Zener diode between

voltage of the Zener diode. However, for the lowest

significantly below the Zener breakdown voltage, it is

recommended that a 0.22

µF ceramic chip capacitor be

As a general rule, the ESD Protection Array should be

located as close as possible to the point of entry of

expected electrostatic discharges. The power supply

bypass capacitor mentioned above should be as close

minimum PCB trace lengths to the power supply,

ground planes and between the signal input and the

ESD device to minimize stray series inductance.

Additional Information

See California Micro Devices Application Note AP209,

“Design Considerations for ESD Protection", under

Applications at www.calmicro.com.

Figure 4. Application of Positive ESD Pulse between Input Channel and Ground

N

V

PATH OF ESD CURRENT PULSE I

ONE

CHANNEL

OF

CM1209

CHANNEL

INPUT

GROUND RAIL

CHASSIS GROUND

POSITIVE SUPPLY RAIL

SYSTEM OR

CIRCUITRY

BEING

PROTECTED

LINE BEING

PROTECTED

ESD

0.22µF

2

D

0A

20A