Transient Voltage Suppressors (TVS) for

Automotive Electronic Protection

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Document Number: 88490

2

Revision: 09-Aug-10

Application Note

Vishay General Semiconductor

Fig. 3 - Parameters of Voltage and Current

PRIMARY PROTECTION OF THE AUTOMOTIVE POWER LINE (LOAD DUMP)

Automotive electronics, such as electronic control units,

sensors, and entertainment systems, are connected to one

power line. The power sources for these electronics are the

battery and alternator, both of which have unstable output

voltages that are subject to temperature, operating status,

and other conditions. Additionally, ESD, spike noise, and

several kinds of transient and surge voltages are introduced

into the power and signal line from automotive systems that

use solenoid loads, such as fuel injection, valve, motor,

electrical, and hydrolytic controllers.

Fig. 4 - Typical Vehicle Power Bus

What is Load Dump?

The worst instances of surge voltage are generated when

the battery is disconnected when the engine is in operation,

and the alternator is supplying current to the power line of

the vehicle. This condition is known as “load dump”, and

most vehicle manufacturers and industry associations

specify a maximum voltage, line impedance, and time

duration for this load dump status, as shown in Figure 5.

Fig. 5 - Output Voltage of Alternator in Load Dump Condition

Two well-known tests simulate this condition: the U.S.’s

ISO-7637-2 pulse 5 and Japan’s JASO A-1 for 14 V

powertrains and JASO D-1 for 27 V powertrains. In this

section we review the application of TVS for load dump in

14 V powertrains.

Specification and Results of Load Dump Tests

The U.S.’s ISO-7637-2 pulse 5 and Japan’s JASO A-1 tests

for 14 V powertrains are simulated in Table 1.

Reverse

Voltage

I

F

V

F

I

R

I

PP

V

WM

V

BR

V

C

Reverse

Current

Forward

Voltage

Forward

Current

A

TCU

ECU

Air-Bag

ABS

Car-Audio

& ......

Battery

Regulator

ESD or Lightning

High Voltage induced

by Alternator

Reaction Transient

from Motor and Spark Plugs

A

Load

X

Output Voltage of Alternator

Battery

Connected

Battery

Disconnected

V

P

V

N

TABLE 1 - MAJOR LOAD DUMP TEST CONDITIONS FOR 14 V POWERTRAINS

(V)

(V)

(V)

(

Ω)

TIME

(ms)

CYCLE TIME

JASO A-1

70

-

12.0

0.8

200

1

88

-

12.0

1.0

200

1

ISO 7637-2 pulse 5

78.5 to 100.5

65 to 87

13.5

0.5 to 4.0

400

1