Robust Automotive Supply Protection for ISO 7637-2 and ISO 16750-2 Compliance: Page 9 of 9

October 22, 2017 // By Dan Eddleman, Linear Technology (Analog Devices)
Automotive power supplies produce formidable transients that can readily destroy exposed onboard electronics. Over time, as electronics have proliferated in vehicles, automotive manufacturers have duly noted failures, compiling a rogues’ gallery of the responsible power supply transients. Manufacturers have independently created standards and test procedures in an effort to prevent sensitive electronics from falling prey to these events. Recently, though, automotive manufacturers have combined efforts with the International Organization for Standardization (ISO) to develop the ISO 7637-2 and ISO 16750-2 standards, which describe the possible transients and specify test methods to simulate them.

ISO 7637-2 Requirements

While the power quality portions of ISO 7637-2 moved to ISO 16750-2 in 2011, pulses 1, 2a, 2b, 3a, and 3b are still contained in ISO 7637-2.

Pulse 1

Pulse 1 describes the negative transient observed by electronics connected in parallel with an inductive load when the connection to the power supply is interrupted. Pulse 1 begins with the supply voltage collapsing to 0V as the supply voltage is removed. Soon thereafter, a −150V pulse is applied with a 2ms decay time. The energy of the negative pulse is limited by the 10Ω series resistance.

Pulse 2a

Pulse 2a describes the positive voltage spike that may occur when current is interrupted to a circuit in parallel with the electronics being tested. If current is built up in the wiring harness, when a device suddenly stops sinking current, the energy stored in the wiring harness inductance may cause a voltage spike. The energy of this positive spike is limited by a 2Ω series resistance.

Pulse 2b

Pulse 2b defines a situation that occurs when the ignition is switched off and DC motors act as generators. For example, if the heater is running when the driver

 turns off the car, for a short time the blower motor can supply DC power to the system while it spins down.

Pulses 3a and 3b

Pulses 3a and 3b are the negative and positive spikes that may occur as a result of switching processes including arcing across switches and relays. For this specification, the energy is limited by a 50Ω series resistance.

 

Independent Test Report

The LTC4380 has been tested for ISO 7637-2 and ISO 16750-2 compliance by an independent test facility. The full test report is available at www.linear.com/docs/56650.

About the author:

Dan Eddleman is Senior Applications Engineer, Mixed Signal Products (now part of Analog Devices).

 

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