The test conditions are generally tighter for automotive products than for typical consumers products, since the safety of driver and passengers is involved and it is necessary to ensure that the vehicle runs properly. Most of the EMC test regulations are designed specifically for vehicles, and that’s why the automotive electronics certification is almost independent of other fields. This article aims to explore the EOS tests defined for automotive OEMs, ISO standards and the adopted EOS solutions based on years of experience collected by Amazing Microelectronic in the automotive market.
ISO 7637 standard
IEC 61000-4-5 is in general used as the EOS test standards for typical consumer products. However, this test is rarely performed in the field of automotive, since the environment on board a car is quite complicated. During an EOS test, it is necessary to simulate what really happens on board a vehicle; for example, an artificial network is built to simulate the impedance of wire harness in a car, and high-current circuit breaker is used to realize the scenario where the car’s power supply system is connected/disconnected. All the test conditions are defined in ISO 7637 [1]. The ISO 7637 series is titled “Road vehicles -- Electrical disturbances from conduction and coupling”. ISO 7637-2 [2] specifies only the transient disturbances along “power supply lines”, while ISO 7637-3 [3] defines the transient disturbances induced by capacitance and inductance along all lines except power supply lines.
The delivery specifications of many automotive OEMs are based on ISO 7637 standard, and the test parameters are modified to meet the corporate automotive needs. For Tier 1, the tests are performed on modules according to specifications developed for OEMs. Passenger cars, the vehicle category with the highest market share, run on 12 V power system based on which all the test specifications mentioned in the article are written.
Transient disturbance resistance test of power supply lines
Table 1 provides the 5 waveforms defined in ISO 7637-2, namely Pulse 1, 2a, 2b, 3a and 3b, each of which is generated for a specific event that occurs to on-board wiring. The waveforms are generated by a test module during the test to simulate the environment in which real events occur. Among them, Pulse 2b is flexible and performed only when it is specified by OEMs. Generally, the test requirements are taken into consideration in the design stage for Tier 1, and production devices complying with ISO 7637 are adopted for better resistance of module to disturbances. For example, in-house tests (with the equipment shown in Fig. 1) have proven that the AZ9424-01G of Amazing Microelectronics meets level IV, the highest level recommended by ISO 7637-2, which is the Pulse 1, 2a, 3a and 3b voltages in Table 2. It protects the internal power supply lines on board of a vehicle and lowers the risks of failures during testing and future EOS issues at the customers.
Figure 1 ISO 7637-2 test equipment at the test lab of Amazing Microelectronic
Pulse 1 | Description | Example | Duration |
| A part is connected to an inductance load in parallel. If the power supply line is open suddenly, the voltage across the inductance load will be applied reversely to power supply end of the part, resulting in a negative transient voltage, Pulse 1. | A transient negative voltage occurs to the coil of the brushless fan motor as its power is turned off. | 2 ms | |
| |||
Pulse 2a | Description | Example | Duration |
| The parasitic inductance in the power supply harness causes change in current when the parallel load is disconnected, generating and feeding a positive voltage to power supply. | When the LED is turned off, the current decreases, and the parasitic inductance on the harness starts to discharge. | 0.05 ms | |
 | |||
Pulse 2b | Description | Example | Duration |
| A part is connected to a DC motor in parallel. When the engine is turned off, the DC motor suddenly becomes an equivalent generator and generates and feeds a positive voltage to power supply. | While the pump is running, the power is disconnected, and the motor continues to rotate due to inertia, and generates a transient. | 0.2 s ~2 s | |
 | |||
Pulse 3a/3b | Description | Example | Duration |
| When a mechanical switch is disconnected, the switching action generates an arc, which in turn generates a high-speed cyclic transient. | The ignition is turned off, and the power supply generates a spark. | 150 ns ± 45 ns | |
| |||
ISO 7637-2 | Level IV | Level III | Level I/ II | Number of Pulses or Test Time |
Pulse 1 | -150 V | -112 V | -75 V | 500 Pulses |
Pulse 2a | +112 V | +55 V | +37 V | 500 Pulses |
Pulse 2b (Optional) | +10 V | +10 V | +10 V | 10 Pulses |
Pulse 3a, 3b | -220 V, +150 V | -165 V, +112 V | -112 V, 75 V | 1 hour |
Test methods for transient disturbance resistance of CAN bus
There are CAN (Controller Area Network), LIN (Local Interconnect Network) and FlexRay for on-board buses, where CAN is the most widely used on-board communication interface. The CAN bus is subject to tests according to ISO 7637-3, since it is considered a signaling cable.
It is learned from the examples in Table 1 that the 5 pulses defined in ISO 7637-2 are events directly applied to power supply lines. The corresponding disturbance waveforms are injected to these lines directly for testing. For signaling lines, however, indirect disturbances are generated by coupling. There are 3 test methods in ISO 7637-3 to couple pulses to signals, namely capacitive coupling clamp (CCC), direct capacitive coupling (DCC) and inductive coupling clamp (ICC). The Fast a and Fast b waveforms defined are based on Pulse 3a and 3b in ISO 7637-2, except that the appropriate one of the three method is to be selected for coupling for the transient disturbance resistance test of signaling lines.
Amazing Microelectronic provides the dual-channel AZ9424-02S family for the differential signals on CAN bus. Apart from highly efficient ESD protection capability, it has the resistance to transient disturbances. Table 4 presents the results ISO 7637 tests performed on AZ9424-02S at a third-party lab. With DCC, it passed Pulse 3a and 3b (Fastａ/ Fast b) with a voltage up to ±200 V, far better than the highest test level in ISO 7637-3 (Level IV in Table 5).
For an automotive module to pass successfully the ISO 7637 system tests for CAN bus, designers have to evaluate the specifications of protection devices in particular, and the transient disturbance resistance of the CAN transceiver itself needs to take into consideration. The ISO 7637 tests for CAN transceiver are also included in IEC 62228-3 [4]. This document is the electromagnetic compatibility standard specified for CAN transceivers evaluated by automotive OEMs. The complete CAN transceiver family of Amazing Microelectronic has passed the maximum test voltage specified in IEC 62228-3 for transient disturbance resistance (Table 3), and the automotive transceiver products are certified by a third-party lab in Germany.
|
Test Pulse |
Voltage Level |
|
1 |
-100 V |
|
2a |
+75 V |
|
3a |
-150V |
|
3b |
+100 V |
Amazing Microelectronic has more solutions for automotive buses in addition to CAN bus. FlexRay and CAN both run on differential signals and, therefore, the dual-channel AZ9424-02S may serve as the ISO 7637 protection solution in both cases. LIN, on the other hand, transmits signals through single-end. The single-channel AZ9824-01L is recommended in this case. The details are provided in Table 4.
| P/N |
Vrwm |
Package |
ISO 7637-2 Pulse 3a, 3b (DCC) |
Cap. |
ISO 10605 ESD (330 Ω/ 150 pF) |
ESD Clamping Voltage (at TLP 16 A) |
Applications |
| AZ9424-02S |
±24 V |
SOT23-3L |
±200 V |
38 pF |
±25 kV |
±31 V |
Classical CAN |
| AZ9824-01L |
+24 V, -15 V |
SOD-323 |
±600 V |
55 pF |
±30 kV |
+21 V, -31 V |
Classical CAN, LIN bus |
Table 4 Automotive bus solutions: AZ9424-02S and AZ9824-01L parameters
|
ISO 7637-3 |
Level IV |
Level III |
Level II |
Level I |
Test Time |
|
Fast a |
-60 V |
-40 V |
-20 V |
-10 V |
10 min |
|
Fast b |
+40 V |
+30 V |
+20 V |
+10 V |
10 min |
Conclusions
There are so many automotive EOS tests, and this article talks about the electric disturbance tests in ISO 7637 for 12 V power system. Should a module under test be used in a commercial vehicle or run on 24 V, please consult the test specifications in ISO 7637-2 or call Amazing Microelectronic. Also, OEMs evaluate their own needs and modify ISO 7637 into their own version of automotive specifications. For example, a car manufacturer is known to incorporate test methods for 48 V power system additionally for the tests on 48V modules used in their light hybrid models, as well as waveforms other than those in Table 1 and test voltages other than those recommended by ISO 7637. Module manufacturers are recommended to work on OEM test requirements in the design stage, and talk to device suppliers about the ISO 7637 specifications of the intended devices, ensuring that they have compliant disturbance resistance and preventing the waste of time for repeated certifications.
Reference
[1] ISO 7637 Road vehicles -- Electrical disturbances from conduction and coupling Third edition 2011-03
[2] ISO 7637-2 Part 2: Electrical transient conduction along supply lines only 2016-07
[3] ISO 7637-3 Part 3: Electrical transient transmission by capacitive and inductive coupling via lines other than supply lines Second edition 2007-07
[4] BS EN IEC 62228‑3:2019 Integrated circuits - EMC evaluation of transceivers Part 3: CAN transceivers Chapter 6.3 Immunity to impulses