Detailed explanation of automotive EMI/EMC test standard ISO7637-2

At present, the popular automotive electronics standard ISO7637 is often encountered, so I think it is necessary to give you a simple and clear introduction to the general content of this standard so that you can use the solution in a targeted manner.

(I) Test pulse classification:

W/A/S/T/E

Test pulse 1: It simulates the transient phenomenon generated when the power supply is disconnected from the inductive load. It is suitable for various modules that are directly connected in parallel with the inductive load when used on vehicles. P1 pulse has a large internal resistance (10~50Ω), a high voltage (tens of volts to hundreds of volts), a fast leading edge (microseconds) and a large width (milliseconds). It is a medium-speed and medium-energy pulse interference in the entire ISO7637-2 standard, and it has both interference (causing equipment malfunction) and destruction (causing damage to components in the equipment) on the tested equipment.

Test pulses 2a and 2b

W/A/S/T/E

Pulse 2a simulates the transient phenomenon caused by the sudden interruption of current in the device connected in parallel with the module due to the inductance of the wiring harness. The P2a pulse is a pulse interference with fast speed and small energy in the entire ISO7637-2 standard. Its function is somewhat similar to the P1 pulse, but it is a positive pulse.

Pulse 2b simulates the transient phenomenon when the DC motor acts as a generator and the ignition switch is disconnected. The P2b pulse is a pulse with low voltage (roughly equivalent to the system power supply voltage), slow leading edge (milliseconds), large width (up to seconds) and small internal resistance. In the entire ISO7637-2 standard, it belongs to low-speed and high-energy pulse interference, focusing on the destructiveness to equipment (components). The effect of the P2b pulse is somewhat similar to P5, but the voltage is lower and the pulse is wider.

Test pulses 3a and 3b: Test pulses simulate transient phenomena caused by switching processes. The characteristics of these transient phenomena are affected by the distributed capacitance and distributed inductance of the wiring harness. P3 pulses are a series of high-speed, low-energy small pulses in the entire ISO7637-2 standard, which can often cause malfunctions in equipment controlled by microprocessors or digital logic.

Test pulse 4: simulates the drop in power supply voltage when the starter motor circuit of the internal combustion engine is powered on, excluding the peak voltage during starting. When the starter of the internal combustion engine is powered on, the power supply voltage drops, generating pulse 4. The P4 pulse in the ISO7637-2 standard is mainly used to assess the malfunction of the equipment during the fall process, especially to assess whether the equipment with microprocessors has data loss and program disorder.

Test pulses 5a and 5b:

W/A/S/T/E

Simulate the transient phenomenon of load dump. When the battery is disconnected (power-deficient state), the AC generator is generating charging current, and there are still other loads on the generator circuit. The current in the coil of the generator is large when it is not disconnected, and suddenly the current decreases when it is disconnected, generating a reaction potential.

抛负载的幅度取决于断开电池连接时，发电机的转速和发电机的励磁场强的大小。抛负载脉冲宽度主要取决于励磁电路的时间常数和脉冲幅度。大多数新型交流发电机内部，抛负载幅度由于增加限幅二极管而受到抑制(箝位)。

Load dump may occur due to cable corrosion, poor contact or disconnection from the battery while the engine is running.

The P5 pulse has a high amplitude (100~200V, which is considered high voltage compared to the system power supply voltage), a large width (up to several hundred milliseconds), and a very low internal resistance (several ohms, or even a few tenths of an ohm). Therefore, in the ISO7637-2 standard, the P5 pulse is a pulse with relatively high energy. In addition to assessing the anti-interference ability of the tested equipment under the action of P5, it is also currently assessing its destructiveness to the equipment components.

(II) Functional status classification:

The following classification is used for the functional status of an assembly or system

W/A/S/T/E

Category A: The device or system can perform all its pre-designed functions during and after the application of disturbance.

Class B: The device or system can perform all its pre-designed functions during the application of disturbance; however, one or more indicators may exceed the specified deviation. All functions automatically return to the normal working range after the cessation of the application of disturbance. The storage function should maintain the Class A level.

Category C: The device or system does not perform one or more of its pre-designed functions during the application of disturbance, but can automatically return to normal operation after the disturbance stops.

Category D: The device or system does not perform one or more of its pre-designed functions during the application of disturbance, and can only return to normal operation after the disturbance is stopped and a simple "operation or use" reset action is performed.

Category E: The device or system does not perform one or more of its pre-designed functions during and after the application of disturbances, and its normal operation cannot be restored without repairing or replacing the device or system.

Note: “Function” here refers to the function performed by the electrical/electronic system.

(III) Auxiliary instructions for experimental level

W/A/S/T/E

a Test pulse is the same as the standard pulse

b Value agreed upon by vehicle manufacturer and equipment supplier.

c The amplitude is the Ua value determined for each test pulse in the standard pulse.

d Since the minimum number of test pulses is 1, the pulse cycle time is not given. When multiple pulses are applied, a minimum delay of 1 min should be allowed between pulses.

e The test level reflects the load dump condition of the generator at rated speed. If concentrated load dump protection is used, the determined test pulse 5b and the values ​​in the specified table are applied.

f Number of pulses or test time for durability test. Number of pulses or test.

g Levels I and II are deleted because these levels do not ensure adequate noise immunity in road vehicles.

(IV) Determination of functional status classification of test pulse severity

Manufacturers and users should specify the functional status classification of the device and the test pulse severity level to clarify the specific application of the device.

Test pulses may be ignored if they do not reach the real conditions of the specified device - the conditions under which the device is used in a vehicle.

Class C functional defects are acceptable for devices that do not have to operate when a specific pulse occurs (such as a flasher during startup).

Class D functional defects are acceptable for devices that do not cause customer complaints or inconvenience failures.

Category E functional defects are used primarily for test report purposes and are generally unacceptable except under special circumstances.

For details, please refer to ISO7637-2. This article only provides a simple analysis.