EMC FLEX BLOG A site dedicated to Automotive EMC Testing for Electronic Modules

Types of load dump transient generators

The high energy content of load dump pulse require specialized pulse generators like classic LCR or DC amplifier based pulse generators.

E.1 Determination and verification of pulse generator minimum energy capability
E.1.1 Calculation method
This method is used to calculate the energy of the pulse as delivered by the generator to the matching resistor (resistive load RL ), utilizing the measured pulse parameters td and Us.
The transient generator used shall generate double exponential transients, which are a result of capacitive discharges into a pulse shaping network. This type of generator is applicable to pulses 1 (12 V), 1 (24 V), 2a, 3a/3b and 5.

SAE J1113-11 (2007)
The Load Dump Pulse Suppressed or Unsuppressed  is defined regardless to specification used by (Us) Peak Voltage in Volts, (Ri) Internal Resistance in ohms, and (td) Duration in ms.



The precise characteristics of suppressed load dump pulse varies based on automotive OEM type of centralized LD suppressor used. The testing methodology is periodically adjusted to accommodate new type of electronic devices. As of today most OEM specifications tend to relay on ISO 16750 for Load Dump.

GM9105P Pulse#6 (LD)

• DUT that operate in a vehicle using avalanche/zener diodes in the alternator for LD protection
• suppressed LD must be clamped to the avalanche diode clamp level.
• DUT that provide vehicle LD protection must be tested to verify
• the peak current sinking capability
• the clamping voltage under load
• DUT expected to sink greater than 40 amps peak current (e.g., engine controller)
• tested with an additional 1 ohm of resistance in series with the simulator.
• DUT expected to sink greater than 25 amps peak current (e.g.,airbag control module)
• tested with an additional 2 ohms of resistance in series with the simulator.
• For both cases
• the clamping voltage under load, across the DUT, must be less than 40 volts
• For all other DUT
• open circuit pulse is clamped to an equivalent vehicle system level (40 V maximum, ramping to 35 V max at 100 ms and 25 V max at 200 ms) by connecting a vehicle suppression model in parallel across the load dump output

Case #2

• LD protection in a (single) centralized location
• The engine controller, airbag control module or other modules are not expected to sink load dump current.
• DUT that provide a centralized load dump clamp (e.g. zener protected power distribution center or PDC)
•  tested with the full simulator output with no additional series resistance.
• For all other DUT
• this open circuit pulse is to be clamped to an equivalent vehicle with simulated avalanche/zener diode suppression in the alternator system level (36 V maximum) by connecting an alternator simulator suppression model in parallel across the load dump output.

Case #3

• Alternator avalanche/zenner diode load dump protection
• LD test pulse applied to the DUT must be clamped to the avalanche/zener diode clamp level (32 V maximum) by an alternator equivalent suppression model.

Test Pulse #5B as delineated in LP-388C-36

• The suppression network shall be connected to the load dump simulator with a wire length of 20cm and in parallel with the DUT.
  
• Test all DUT supply terminals together.
• Leads to be load dumped include the following: battery, ignition and any other input and/or output sourced from battery or ignition voltage as configured in a DUT's complete vehicle system.
• Isolate any exerciser circuits, which are meant to simulate other electronic module peripherals to the DUT.
  
• Do not apply the transient to support equipment.
  
• The DUT supply voltage shall be provided through the load dump simulator, while the DUT exerciser shall be powered from a separate supply. The negative terminal for the two power supplies shall be connected together.

Suppression Module Verification

• Before the test, the Suppression Module must be verified with 13.5 dc volts offset.
  
• The output waveform is evaluated using the specifications defined in PF-9326.
  
• The results of both open and loaded measurements must be documented.

Load Dump Simulator Impedance Verification
The load dump waveform shall be verified with the output open-circuited and shall be evaluated using the specifications defined in PF-9326. Verify that the effect is not caused by the transient interfering with the DUT support equipment. If there is suspicion that the load dump is interfering directly with components of the DUT exerciser, measure the pulse amplitude appearing at the input to the exerciser component which is not meant to be tested. If a substantial amplitude is present, investigate by removing such components.



ES-XW7T-1A278-AB CI 240
A load dump typically occurs during a vehicle-to-vehicle jump start when the jumping vehicle can experience a significant load dump or due to a loose battery terminal. It represents sudden disconnection of load from alternator. Max voltage ESC is exposed to is about 45 V.

• Open Circuit: Vbat+ 60V, 300 ms
• Loaded Circuit: (R = 0.7W): Vbat+30 V, 150 ms

EMC-CS-2009.1 CI 220 Pulse G2 (Centralized Load Dump)
Practically the same CLDS suggested by SAE J1113-11.


FMC1278 Rev 2 CI 222 (Suppressed Load Dump Pulse 5b )



DUT Load Dump Protection using TVS Diodes
1. Darlington LD Suppression Circuit for low current consumption devices



2. P-FET LD Suppression Circuit



3. P-FET LD Suppression with Isolation Switch Circuit



Summary
1) TVS Diodes are used to protect DUT from various supply line transients


2) For vehicle having centralized load dump protection the test pulse used is ISO 7637-2:2004 (ISO 16750) 5b.
3) Avalanche diodes or Zener diodes are used in alternators to suppress the load dump to a voltage defined by automotive OEM.

The generic shielding effectiveness requirement is 40 dB for magnetic field, electric field, and plane waves. Depending on the application the frequency range can start from 10 Hz going up to GHz.

To predict shielding effectiveness (SE) of a metal sheet the following factors are summed:  Absorption Loss (A), Reflection Loss (R), re-Reflection Correction Factor (C).  SE = A + R – C (see MIL-HDBK-419A).

Absorption loss depends on material thickness, permeability, electrical conductivity, and the frequency of the incident wave.  It is the same for all electromagnetic waves.

Reflection loss depends on the distance of the EMI source to the material (different for electric, magnetic, and plane waves), material electrical conductivity, and the frequency of the incident wave.

• Materials_for_electromagnetic_interference_shielding.pdf (388.20 kb)
• Engineering_Aspects_of_Electromagnetic_Shielding.pdf (9.47 mb)
• IEEE-299-1997.pdf (502.42 kb)
• MF_SE_of_thin_conductive_coatings.pdf (282.80 kb)
• Predicted_and_measured_EMI_shielding.pdf (668.60 kb)
• Properties_of_metals_used_for_RF_shielding.pdf (4.80 mb)
• Shielding_Effectiveness_Superalloy_Aluminum_Mumetal_Shielding_Tapes .pdf (443.55 kb)

The Bulk Current Injection (BCI) test method simulates a field-to-wire coupling from nearby low frequencies radiated fields induced onto a test harness small relative to wavelength.
The coupling from BCI probe will increase with test frequency when the cable is electrically short, and then flatten out when the cable approaches and exceeds a half-wavelength in length.

The transducers (RF current transformers) inject current into both sides of the test harness, therefore both DUT and Load Simulator are subject to test. RF radiation from load simulator cables is possible, but it can be reduced placing 20cm of clip-on split-ferrite RF suppressers close to the transducer.

The BCI common-mode current injected in the test harness simulates an illuminating RF field.
To simulate conducted differential-mode disturbances the BCI induced current is injected in individul conductors.

Using the Substitution Method the actual current injected in test cables can vary from what was initially  calibrated, being less likely to over-test but more real-life representative.

To ensure the repeatability of test results, the cable under test must be centered within BCI current probe, the test set-up must be consistent, especially cable routing, placement of the clamp, and proximity to metal structures.

BCI Calibration Levels per MIL STD 416F CS114:

CAN Bus Off is an error state of the CAN controller and it can be set only by the Transmitter Node when Transmit Error Counter is above 255. Such critical error is usually the result of a critical hardware issue (e.g. high level of electromagnetic field, bus wiring short-circuit, defective transceiver).

Methods to self-recover from a Node CAN Bus Off state:

1) Automatically after the CAN controller generates an interrupt.

2) Manually upon User request (ISO11898-1 §6.15).

In both the above  instances the bus turns back on after 128 occurrences of 11 consecutive Recessive Bits (BOSCH CAN 2.0B §8.12).

Auto-Bus-ON is not required by ISO 11989, therefore the CAN controller makers let the application to decide on its implementation. The automotive industry does not encourage the auto-bus-on feature.

If application's driver reports repeatedly the CAN Bus Off state the application should stop using the CAN.

Christian Rosu

The data is carried on the CAN bus as a voltage difference between the two signal lines. If both lines are at the same voltage, the signal is a recessive bit. If the CAN_H line is higher than the CAN_L line by 0.9V, the signal line is a dominant bit.

Immunity to Ground Noise

The CAN bus does not use the ground as reference point for these two signal lines. Therefore the CAN bus transmissions lines are immune to any ground noise typically present in automotive applications.

Immunity to Electromagnetic Filed

The signals on the two CAN lines will both be subject to the same electromagnetic filed level. Therefore no differences in voltages between the two lines should become relevant under electromagnetic interference.

Using Twisted Pair Wires for Differential Signal Lines

Bad connectors are almost guaranteed to present an impedance discontinuity, and hence will cause reflections. Transmission line stubs of any length are also a source of reflections, longer the stub, the worse the impact of the reflections on lower data rate signals. Reflections are bad because they can cause destructive interference that can corrupt any transmitted data.

Christian Rosu