Tvs Diode Array Spa Diodes Page 13 TVS Diode Array SPA Diodes Catalog

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 02/23/17 TVS Diode Arrays (SPA Diodes) ESD Immunity Test Standards To test their products, manufacturers may apply one of several methods using either the CDM (Charged Device Model), MM (Machine Model), and/or HBM (Human Body Model). MIL-STD-883 Method 3015 and IEC61000-4-2 are testing standards commonly applied: MIL-STD-883 Method 3015 Historically, analog and digital designers have been required to have ESD protection "on-chip" to protect the IC during manufacturing. The most commonly used ESD standard in the manufacturing environment is the MIL-STD-883, Method 3015 and it's also referred to as the Human Body Model (HBM). This model discharges a 100pF capacitor through a 1500 resistor into the device under test. The table below points out the four test levels as defined in the standard. HBM Level Contact Discharge (kV) Peak Current (A) 1 0.5 0.33 2 1 0.67 3 2 1.33 4 4 2.67 The maximum level required for a typical IC had been 2kV up until 2007, but today that level has been drastically reduced to 0.5kV. Obviously, this has helped chip designers save valuable silicon area for more functionality, but in turn, it has made the IC much more susceptible to damage from ESD. IEC61000-4-2 Conversely, equipment manufacturers have traditionally used an ESD standard defined by the IEC (International Electrotechnical Commission) for system or application level testing. This model uses a 150pF capacitor which is discharged through a 330 resistor. The table below displays the four test levels as defined in the standard. IEC Level Contact Discharge (kV) Peak Current (A) 1 2 7.5 2 4 15 3 6 22.5 4 8 30 Most all manufacturers require that their equipment pass Level 4, or 8kV, as a minimum, however, some are looking for increased reliability and require that their devices pass a much higher level like 15kV or 30kV. The system level ESD test defined by the IEC produces a substantial increase in peak current compared to the military standard. If an IC is rated for 0.5kV per the MIL- STD and the equipment manufacturer tests this same IC at 8kV per the IEC specification, the chip will see nearly a 100 fold increase in peak current (i.e. 0.33A vs. 30A)! Additional Transient Immunity Considerations Film Resistors In-line film resistors between inputs and off-board connectors provide minimal transient protection and are often damaged themselves. Component Quality Active components play the biggest role towards ESD/ Transient immunity. If using substitute and/or secondary source components, test and analyze them thoroughly. Though functionally equivalent, they may lack the ESD/ Transient immunity of the preferred components. Multi-Suppressor Combinations ESD protection through use of SPA Diodes included in combination with other filters and transient suppressors is another strategy for inputs, outputs and power ports. See www.littelfuse.com for more information. Preventive Software Programming The basic requirement of good software is to cleanly handle abnormal operations, no matter the cause. Internal Moving Parts Equipment with moving parts can become its own ESD/ Transient generator. Printers and copiers are especially susceptible because they carry paper through paper rollers and use toner. In general, the problem areas include sliding parts, rolling parts, flexing parts, flowing liquids and airflow carrying particles or liquid droplets. Finally, once the design has been approved, it's tempting to substitute components in effort to boost product performance. Often newer chips and components are faster but more sensitive to transients causing new emissions and immunity problems. Keep fully informed, as periodically suppliers can make changes to components that may affect ESD Immunity. Test the new parts to determine if they are still effective. Planning is key, in the event the new product doesn't work or the company ceases producing it, having several backup plans will help your company face unforseen challenges. For More Information Please visit www.littelfuse.com/esd for technical notes and application advice articles that address ways to reduce catastrophic failures and allow the equipment to reliably withstand certain ESD events. ESD Suppression Strategies and Standards (continued)

Previous Page
Next Page