VISHAY Load Dump TVS Series for 24 V Powertrains By Soo Man (Sweetman) Kim As more trucks and buses are built with complex electrical systems, load dump protection is an important safety feature for vehicles with 24 V powertrains. This article describes the changes to the load dump test condition and defines the maximum surge suppressing capability for Vishay load dump TVS series in these conditions. The New ISO Standard ISO-16750-2 (2010) vs. the Old ISO Standard ISO-7637-2 (2004) The most significant difference between the new and old load dump tests is that the new standard (ISO-16750-2, 2010) requires 10 pulses in 10 minutes with a one-minute interval per pulse, as shown in Table 1. The old standard (ISO-7637-2, 2004) required only a single pulse. Table 1: Pulse requirements for ISO-16750-2 Type of system Parameter UA = 12 V UA = 24 V US (V) 79 to 101 151 to 202 Ri (Ohm) 0.5 to 4 1 to 8 td (ms) 40 to 400 100 to 350 tr (ms) 10 / +0 / -5 10 / +0 / -5 Minimum test requirements 10 pulses at intervals of 1 min. The test condition of the 10 pulses in 10 minutes shows the reliability of the load dump protection device, which assists the circuit designer in selecting the best device based on surge capability in high-temperature conditions. Load Dump Protection for 24 V Systems Using an AEC-Q101-Qualified TVS Series Device Figure 1 illustrates the load dump protection device clamping in the specified voltage range, which is different from the standard waveform. The active voltage range of the clamping device in the load dump pulse is the reason for this difference, as shown in Figure 1. The device in Figure 2 is clamping at 202 V US, 3.5 Ω Ri, and a 350 ms pulse width. VISHAY INTERTECHNOLOGY, INC. Corporate Headquarters: 63 Lincoln Highway, Malvern, PA 19355-2120, U.S.A. Phone: 610- 644-1300 Fax: 610-296-0657 www.vishay.com ONE OF THE WORLD’S LARGEST MANUFACTURERS OF DISCRETE SEMIC ONDUCTORS AND PASSIVE COMPONENTS Figure 1: Input waveform of an ISO-16750-2 pulse: 5 A, 201 V Us, 350 ms pulse width condition Figure 2: Clamped waveform of the SM8S36A at an ISO-16750-2 pulse: 5 A, 202 V US, 3.5 Ω Ri, 350 ms pulse input condition VISHAY INTERTECHNOLOGY, INC. Corporate Headquarters: 63 Lincoln Highway, Malvern, PA 19355-2120, U.S.A. Phone: 610- 644-1300 Fax: 610-296-0657 www.vishay.com ONE OF THE WORLD’S LARGEST MANUFACTURERS OF DISCRETE SEMIC ONDUCTORS AND PASSIVE COMPONENTS Protecting Electronic Devices in Load Dump Status by Using a TVS Device The function of a load dump protection device is to keep the clamping voltage under the maximum input voltage of the power regulator, or other electronic components in the circuit, without halting or powering down the system. The protection device will not operate until the line voltage reaches 36 V for 1 to 10 minutes or longer, as specified by the vehicle’s manufacturer or as required in withstand test conditions. This means the device does not perform at 36 V in any kind of status in either high- or low-temperature environments. The clamping voltage of the load dump TVS device rises as the junction temperature changes during continuous clamping operation. Figure 3 shows that the operating time of the load dump TVS device is increased when Ri is increased, with an operating time of 300 ms, which is longer than the 3.5 Ω Ri condition shown in Figure 2. Figure 3) SM8S36A at Us = 202 V, Ri = 4.0 Ω, 350 ms pulse width VISHAY INTERTECHNOLOGY, INC. Corporate Headquarters: 63 Lincoln Highway, Malvern, PA 19355-2120, U.S.A. Phone: 610- 644-1300 Fax: 610-296-0657 www.vishay.com ONE OF THE WORLD’S LARGEST MANUFACTURERS OF DISCRETE SEMIC ONDUCTORS AND PASSIVE COMPONENTS Capability of Vishay’s Load Dump TVS Series Using the New Load Dump Test Condition Standard The following graphs show how using the new test condition of 10 continuous pulses affected the surge suppressing capability of the load dump TVS device. Graphs 1 -4: Capabilities of Vishay’s SM5S series in the new load dump test conditions. Suffix “M” lines are multiple pulses using the new test condition standards (ISO16750-2); suffix “S” lines are a single pulse as defined by the old test condition standards (ISO7637-2). Please note that these values are based on normal room temperature environment on a pad size as recommended in the datasheet. Actual capability varies depending on PCB type, pad size and temperature conditions. Clamping capability relating to junction temperature and derating ratio similar to ”Load Dump Power Characteristics” in the datasheet. The following graphs illustrate a solution for low Ri by using two or three devices in a series. VISHAY INTERTECHNOLOGY, INC. Corporate Headquarters: 63 Lincoln Highway, Malvern, PA 19355-2120, U.S.A. Phone: 610- 644-1300 Fax: 610-296-0657 www.vishay.com ONE OF THE WORLD’S LARGEST MANUFACTURERS OF DISCRETE SEMIC ONDUCTORS AND PASSIVE COMPONENTS Figure 4) Derating ratio of the load dump power characteristics at case temperature for the SM5S Series Appendix Easy reference for load dump TVS vs. peak current (A) Total Pulse width Single pulse 10 pulses in 10 minutes 100ms 225ms 350ms 100ms 225ms 350ms SM5S36A 37 30 24 28 24 21 SM6S36A 39 33 27 31 27 23 SM8S36A 56 51 37 46 38 29 SM8S43A 54 49 35 45 37 28 SM8S18A X 2 125 105 83 100 88 67 Sm8S12A X 3 190 165 145 160 130 115 For a more detailed explanation of load dump protection, please refer to the application note “Transient Voltage Suppressors (TVS) for Automotive Electronic Protection”. http://www.vishay.com/doc?88490. VISHAY INTERTECHNOLOGY, INC. Corporate Headquarters: 63 Lincoln Highway, Malvern, PA 19355-2120, U.S.A. Phone: 610- 644-1300 Fax: 610-296-0657 www.vishay.com ONE OF THE WORLD’S LARGEST MANUFACTURERS OF DISCRETE SEMIC ONDUCTORS AND PASSIVE COMPONENTS