Automotive ESD: ISO 10605

From Technical Report (1994) to Released Standard (2001)

 

The ESD standard for automotive electronics (ISO 10605) was issued as a technical report in 1994 and had remained as such until just over 18 months ago (December 2001) when the technical report was revised to form the current released standard (ISO 10605:2001).  Despite its status as a technical report until recently, it was widely adopted within the automotive EMC community and integrated into many OEM EMC specifications. In general the standard was popular and easy to apply, being broadly based on the industrial and commercial equipment standard IEC 1000-4-2 (now EN 61000-4-2: 1995), using similar equipment and methods but with a different body model.

 

Different Body Model

 

The different human body model is used because the automotive environment for ESD is a discharge between capacitors; human-to-vehicle, as the vehicle is (in general terms) an ungrounded system (it is not connected to a reference “earth”).  This is the main difference between EN 61000-4-2 testing and ISO 10605.  The discharge test head (human body model) contains a higher resistance value; 2kW in ISO 10605 compared to 330W in EN 61000-4-2.  The EN standard uses a single value for the body model capacitance of 150pF, in the ISO standard the same value is used for passenger discharge from outside the vehicle.  Occupant discharge is modelled using more than double this capacitance (330pF) in the ISO standard as the vehicle and user are an “enclosed volume” during occupant discharge rather than “parallel plates” for the external passenger condition.

 

The EN standard does incorporate a method for ungrounded systems, with the system allowed to be permanently wired with 1MW bleed resistance (2 x 470kW in series) to ground.  This simulates battery-operated portable and bench-top equipment rather than the unique condition of a large metal-bodied object that an automotive vehicle represents (aerospace is the closest similar field).

 

Changes to ISO 10605 from 1994 to 2001

 

The ISO 10605:1994 standard was well adopted and little overall change was required.  The one major addition introduced in ISO 10605:2001 is the case for testing un-powered (unconnected) ESA’s.  This test condition represents the handling of the ESA prior to vehicle fit, either during line-fit by the vehicle assembly staff or user fit by an after market installer or the vehicle owner/user.  The test maintains the higher resistance human body model, as again the discharge is capacitor-to-capacitor into an ungrounded and un-powered system.  All testing for un-powered devices is done with the 150pF test head, as the ESA and handler are not in an enclosed volume situation.

 

The test levels for the un-powered ESA test are slightly simpler than the powered tests, having only 3 groups (±4kV, ±6kV and ±8kV direct discharge and ±8kV, ±15kV and ±25kV air discharge).  The maximum air discharge level is higher for un-powered ESAs at ±25kV compared to ±15kV for the powered test.   It is difficult to justify such a high test level as most ESD studies suggest corona discharge prevents a human body achieving more than 15kV for a few seconds and then only if vigorously charged.

 

As with the EN standard for ESD testing ungrounded systems, the ESA has to have any accumulated charge bled from it via a 1MW resistance between discharge impacts.  The ISO standard has no provision for this ground bleed to be permanently fitted to the ESA, hence the accumulated charge remains on the ESA for much longer.

 

Comparison to SAE J1113/13

 

The SAE standard in many ways already encompassed many of the changes that were incorporated into the released version of ISO 10605:2001.  SAE J1113/13 already includes the un-powered ESA test case at the same test levels as adopted by ISO 10605:2001.

 

OEM ESD Standards

 

The North American based OEM’s had already incorporated many of the changes as they adopted SAE J1113/13 in preference to ISO 10605.  The main problem in relation to OEM standards is that some of the European OEM’s have used the EN 61000-4-2 for the un-powered test in their internal specifications, using the lower resistor model value and consequently a higher energy discharge into the un-powered, ungrounded ESA. 

 

The use of the EN 61000-4-2 is incorrect for automotive applications in the opinion of the AutoEMC.net team as this EN standard is primarily designed for earth-referenced (grounded) systems, not for ungrounded capacitor-capacitor discharges.  The EN standard produces a more aggressive test and is not as representative of the application environment as the tests contained in ISO 10605 for automotive electronic equipment.  However any product passing the EN test is likely to pass the ISO 10605:2001 tests at similar voltage discharge levels.

 


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