Transient Voltage Suppressors (TVS) for

Automotive Electronic Protection

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Document Number: 88490

4

Revision: 09-Aug-10

Application Note

Vishay General Semiconductor

Two Groups of Load Dump TVS

There are two kinds of load dump TVS for the primary

protection of automotive electronics: EPI PAR TVS and

Non-EPI PAR TVS. Both product groups have similar

operating breakdown characteristics in reverse bias mode.

The difference is that EPI-PAR TVSs have low forward

conditions. This characteristic is important to the reverse

voltage supplied to the power line. Most CMOS ICs and LSIs

have very poor reverse voltage capabilities.

The gates of MOSFETs are also weak in reverse voltage, at

- 1 V or lower. In the reversed power input mode, the voltage

This reverse bias mode causes electronic circuit failure. The

low forward voltage drop of EPI PAR TVSs is a good solution

to this problem. Another method to protect circuits from

reversed power input is utilizing a polarity protection rectifier

into the power line, as shown in Figure 7. A polarity

protection rectifier should have sufficient forward current

ratings, and forward surge and reverse voltage capabilities.

Fig. 7 - Reverse Bias Status

SECONDARY PROTECTION OF THE AUTOMOTIVE POWER LINE

The primary target of protection circuits in automotive

systems is high surge voltages, but the clamped voltage is

still high. Secondary protection is especially important in

24 V powertrains, such as found in trucks and vans. The

main reason for this is the maximum input voltages for most

regulators and DC/DC converter ICs for automotive

applications are 45 V to 60 V. For this kind of application,

using secondary protection, as shown in Figure 8, is

recommended.

Fig. 8 - Secondary Protection Circuit

Adding resistor R onto the power line reduces the

transient current, allowing smaller power-rating TVSs as the

secondary

protection.

Current

requirements

for

microprocessor and logic circuits in electronic units are

150 mA to 300 mA, and the minimum output voltage of a

12 V battery is 7.2 V at - 18 °C, or 14.4 V for a 24 V battery

under the same conditions. In a 24 V battery under the

above conditions, the supply voltage at a 300 mA load is 8.4

V at R = 20

Ω, and 11.4 V at R = 10 Ω at a minimum voltage

of battery of 14.4 V (24 V battery voltage in - 18 °C).

This supply voltage is higher than the minimum input

voltages for most voltage regulators and DC/DC converter

ICs.

Protected

Load

-

TVS

V

F

Current

Reverse

Power Input

+

Load

Current Limiter

Primary

Protection

+

R

Secondary

Protection

Power

Line

Transient

Voltage

Clamped

Voltage

Clamped

Voltage

V

L

V

min.

V

⁄

()

⁄

()

V

⁄

() R

–

()

×

=

V

V

I

R: Resistor value