Application Note

Automotive Circuit Protection using

Littelfuse Automotive TVS Diodes

Safety

Airbags

Battery Disconnect

Anti-rollover

Stability Control

Seat Belt Pre-tensioning

Tire Pressure Monitoring

HID Lighting

Seating Controls/Memory

Ride Control

Theater Lighting

Climate Control

Navigation Systems

Infotainment/Video

Comfort and Convenience

Engine Management

Adaptable Suspension

Advanced Powertrains

Performance and Emissions

Gas Electric

Fuel Cell Electric

Diesel Electric

Li-Ion Polymer

Ultra-capacitors

Hybrid Vehicles

Figure 1. Vehicle Systems Subject to Transient Surge Hazards

The designers of automotive electronics face many technical challenges during the system design process, including designing

methods of protection against a variety of electrical hazards. The three major sources of electrical hazards in these systems are

electrostatic discharge (ESD), lightning, and switching loads in power electronics circuits. Overcoming transient surges that can harm

the vehicle’s electronics is one of the biggest challenges of the design process.

The Challenge

The Solution

Note: For 48V power system with high power surge rating, welcome to contact Littelfuse for technical support and application test)

Protecting automotive electronics includes eliminating transient surges that can damage the control units, infotainment electronics,

sensors, fuel injectors, valves, motors, 12/24/42/48 volts powertrains, and hydrolytic controllers, etc.

What do Littelfuse Transient Voltage Suppression (TVS) Diodes Protect?

As shown in Figure 1, Littelfuse TVS diodes provide protection for four main categories of vehicle systems: safety, performance and

emissions, comfort and convenience, and hybrid vehicles.

In modern automotive designs, all on-board electronics are connected to the battery and the alternator. As indicated in Figure 2, the

output of the alternator is unstable and requires further conditioning before it can be used to power the vehicle’s other systems.

Currently, most of the alternators have zener diodes to protect against load dump surges; however, these are still not sufﬁcient. During

the powering or switching of inductive loads, the battery is disconnected, so that unwanted spikes or transients are generated. If left

uncorrected, these transients would be transmitted along the power line, causing individual electronics and sensors to malfunction or

permanently damaging the vehicle’s electronic system, affecting overallreliability.

Application Note

Figure 2. The Alternator Causes Most of the Transients In a Vehicle’s Electrical System

Voltage

Reg.

Wipers

Airbag

ABS

EEC

Window Motor

BATT

Alternator/Regulator Assembly

(Actual circuit is fully wave rectiﬁed)

Automotive Transient Surge (Not ESD) Standard

Littelfuse is a leading provider of TPSMF4L, TPSMB, TPSMA6L, TPSMC, TPSMD, TP6KE, TP1.5KE, TP5KP, SZSMF, SZ1SMA, SZ1SMB,

SZP6SMB, SZ1SMC, SZ1.5SMC, SLD, SLD5S, SLD6S, and SLD8S Series. TVS Diodes which can provide secondary transient voltage

protection for sensitive electronics from transients induced by load dump and other transient voltage events. These series offer

superior electrical performance in a small footprint package, allowing designers to upgrade their circuit protection without altering their

existing design footprint or to provide more robust protection in new circuit layouts.

Load dump protection requires high energy TVS diodes in the 12 and 24 volt system. For more information on load dump

protection, visit Littelfuse.com.

The automotive market has major two standards that outline protection against transient surges: JASO and ISO7637-2 (Surge) test for

the Japanese, American, and international markets. JASO A-1 outlines test conditions for 14 volt vehicle systems; JASO D-1 outlines

test conditions for 27 volt vehicles.

The following test standards are international and American test standards, which include the load dump, switching transients

and ESD threats.

Reverse

Battery

24V Jump Start

85V Noise

120V Load Dump

Nominal

14V

6V Crank

Figure 3a: Surge Wave of Different Pulses & Its Magnitude

More Information on the ISO7637-2 Pulses:

International Standard ISO7637-2:

• Applies to road vehicles-electrical disturbance by conduction

and coupling

USA National Standard:

• SAE (Society of Automotive Engineers) J1113

• GM 9105, ES-F2af-1316-AA Ford (Visteon)

• Automotive EMC Transition Requirements

■ Pulse 1- Interruption of inductive load – refers to

disconnection of the power supply from an inductive load

while the device under test (DUT) is in parallel with the

inductive load

■ Pulse 2 - Interruption of series inductive load – refers to the

interruption of current and causes load switching

■ Pulse 3 - Switching spikes

■ 3a negative transient burst

■ 3b positive transient burst

■ Refers to the unwanted transients in the switching events

■ Pulse 4 - Starter crank – refers battery voltage drop during

motor start. This always happens in cold weather

■ Pulse 5 - Load dump – refers to the disconnection of the

vehicle battery from the alternator while the battery is

being charged.

■ Pulse 6 - Ignition coil interruption

■ Pulse 7 - Alternator ﬁeld decayPulse 1, 2, 3a, 3b, 5 - Related

to high voltage transient getting into the supply line; Pulse

4 deﬁnes minimum battery voltage. Refer to Figure 3a

and Table 1