How Ideal Diode Controllers Ease ISO 7637-2 and ISO 16750-2 Compliance in Cars

By Jeongil Lee, Linear Power Business Unit Manager

Ideal diode controllers are widely used in automotive power system designs. They protect against reverse-polarity conditions, allowing for the control of popular 12V and 24V DC rail voltages in passenger cars and commercial vehicles, propelled via an internal combustion engine (ICE) or battery. Typical applications include engine control units (ECUs), infotainment systems, advanced driver assistance systems (ADAS), and battery management systems (BMS). 

One of the challenges faced when designing these systems is to comply with the ISO 7637-2 conducted transient voltage pulses and ISO 16750-2 load dump tests. Both are important standards for automotive power systems.

ISO 7637-2

The ISO 7637-2 standard focuses on the electromagnetic compatibility (EMC) of road vehicles. It specifies test methods and procedures to ensure that electrical and electronic equipment can withstand electrical transients conducted along supply lines. These pulse transients can be caused by various events, such as switching operations or load dumps.

• Scope: Applies to 12V and 24V electrical systems in passenger cars and commercial vehicles.
• Tests: Includes bench tests for injecting and measuring transients to simulate real-world electrical disturbances.
• Importance: Ensures that automotive components can handle electrical disturbances without malfunctioning, which is crucial for vehicle safety and reliability.

The transient immunity Test Pulse 1 is a vital test to assess the robustness of electronic devices against the voltage fluctuations that can occur when a supply is disconnected from inductive loads (see Figure 1).

Figure 1. ISO 7637-2 transient immunity Test Pulse 1 simulates transients due to supply disconnection from inductive loads

The specification parameters for ISO 7637-2 Transient Immunity Test Pulse 1 are shown in Figure 2.

Parameters	Nominal 12V System	Nominal 24V System
Output Voltage (Us)	-75V to -150V	-300V to -600V
Output Impedance (Ri)	10ꭥ	50ꭥ
Pulse Width (td)	2ms	1ms
Rise Time (tr)	(1 ) µs	(3 ) µs
Pulse Repetition Period (t1a)	>0.5s
t2	200ms
t3a	<100µs
a    t1 shall be chosen such that it is the minimum time for the DUT to be correctly initialized before the application of the next pulse and shall be >0.5s. b    t3 is the smallest possible time necessary between the disconnection of the supply source and the application of the pulse.

Figure 2. ISO 7637-2 specification parameters for transient immunity Test Pulse 1 in a 12V and 24V nominal voltage system

 

Figure 3. The AP74700Q ideal diode controller meets ISO 7637-2 pulse 1 with a 12V (left) and 24V system (right)

 

ISO 16750-2

The ISO 16750-2 standard addresses the environmental conditions and testing requirements for electrical and electronic equipment in road vehicles. It ensures that automotive components can withstand the various environmental stresses that they might encounter during their lifecycle.

• Scope: Covers a wide range of environmental conditions, including temperature, humidity, vibration, and electrical stress.
• Tests: Includes specific tests for load-dump protection, which simulate the sudden disconnection of a battery from the alternator.
• Importance: Ensures the durability and reliability of automotive electronics under different environmental conditions, enhancing overall vehicle safety.

The ISO 16750-2 transient immunity Test Pulse B is one of the most destructive pulses described in the standard (see Figure 4) with centralized load dump suppression.

Time (t) Test Voltage (U) Supply Voltage (US) Supply Voltage of the Test Generator (UA) Duration of Pulse (td) Rising Slope (tr)

Figure 4. ISO 16750-2 transient immunity Test Pulse B with centralized load dump suppression

 

The specification parameters for ISO 16750-2 transient immunity Test Pulse B are shown in Figure 5.

Parameters	Type of System		Minimum Test Requirements
	UN = 12 V	UN = 24 V
Usa (V)	79 ≤ US ≤ 101	151 ≤ US ≤ 202	5 pulses at 1 min intervals
Us*(V)	35	As specified by customer (typical value 58)
R1a (ꭥ)	0.5 ≤ R1 ≤ 4	1 ≤ R1 ≤ 8
td (ms)	40 ≤ td ≤ 400	100 ≤ td ≤ 350
T3 (ms)	10	10
a    If not otherwise agreed, use the upper voltage level with the upper value for internal resistance or use the lower voltage level with the lower value for internal resistance.

Figure 5. ISO 16750-2 specification parameters for transient immunity Test Pulse B in a 12V and 24V nominal voltage system

 

Figure 6. The AP74700Q ideal diode controller meets ISO 16750-2 Test Pulse B with centralized load dump suppression in a 12V (left) and 24V (right) system

 

Diodes Incorporated (Diodes) offers ideal diode controllers that meet the ISO 7637-2 transient pulses and ISO 16750-2 load dump suppression compliance standards for automotive applications (see Figure 7).

Component	Input AMR Range /V	Input Voltage Range /V	Ext FET	ISO 7637-2 Compliance	ISO 16750-2 Compliance
AP74700Q	-65 to +65	4 to 60	Single	Meets Compliance	Meets Compliance
AP74700AQ	-65 to +70	4 to 65	Single	Meets Compliance	Meets Compliance
AP74701Q	-34 to +65	4 to 60	Single	Meets Compliance	Meets Compliance
AP74502(H)Q	-80 to +80	4 to 75	Dual  (Back to Back)	Meets Compliance	Meets Compliance

Figure 7. Ideal diode controllers from Diodes Incorporated comply with ISO 7637-2 and ISO 16750-2

 

Reference schematics, including proper TVS and application details, are available in the datasheets. Diodes has also released hardware boards with DC-DC and reverse voltage protection.

 

 

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