Transient voltage suppressors (TVS) for automotive electronic protection: Page 2 of 4

March 31, 2011 //By Soo Man Kim
Transient voltage suppressors (TVS) for automotive electronic protection
A major challenge in automotive design is protecting electronics – such as control units, sensors, and entertainment systems – against damaging surges, voltage transients, ESD, and noise that are present on the power line. Transient voltage suppressors (TVS) are ideal solutions for automotive electronic protection and have several important parameters for these applications, including power rating, stand-off voltage, breakdown voltage, and maximum breakdown voltage. Following are definitions for these parameters.
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.

Figure 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.

Figure 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.

Table 1: Major load dump test conditions for 14-V powertrains. For full resolution, click here .

 

Figure 6: For ISO-7637-2 test conditions, the standard condition is a VS range of 65 V to 87 V, and Ri (line impedance) range of 0.5 Ω to 4 Ω.

Some vehicle manufacturers apply different conditions for the load dump test based on ISO-7637-2 Pulse 5. The peak clamped current of the load dump TVS will be estimated by the following equation:

Calculation for peak clamping current

IPP = ( Vin VC) ⁄ Ri

IPP: Peak clamping current

Vin: Input voltage

VC: Clamping voltage

Ri: Line impedance

The current and voltage waveforms of Vishay's SM5S24A in the ISO-7637-2 test of 87V Vs, 13.5V V batt., 0.75 Ohm Ri and 400ms pulse

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