Load dump protection: Old vs. new ISO standards EDN1 of p-protection--Old-.EDN MOMENT1st untetheredspacewalk istaken, February7, 1984·SearchLogin RegisterSoo Man (Sweetman) Kim, Vishay -February 07, 2014TweetShare0Like0For many years, the load dump surge condition test for automobiles was defined in theISO-7637-2 standard and was used by major automotive component manufacturers worldwide. In2010, this standard was replaced by a new automotive load dump test: ISO-16750-2. This articledescribes the changes to the load dump test condition and defines the maximum surgesuppressing capability on an example load dump TVS under those conditions.New vs. old ISO standardThe significant difference between the old and new load dump tests is that the new test requires10 pulses in 10 minutes with a one minute interval per pulse, as shown in Table 1. The old loaddump test (ISO-7637-2, 2004) specified only a single pulse.Table 1 Pulse requirements for ISO-16750-2ParameterType of systemMinimumUA 12 VUA 24 VUs (V)79 to 101151 to 202Ri (Ohm)0.5 to 41 to 8td (ms)40100tr (ms)10 / 0 / -5to 400to 350test requirements10 pulsesat intervals of 1min.10 / 0 / -5The test condition of 10 pulses in 10 minutes shows the reliability of the load dump protectiondevice, which assists the circuit designer in choosing the correct device based on surge capabilityin high-temperature environments.Load dump protection for 12 V systems using an AEC-Q101-qualified TVS seriesFigure 1 shows the load dump protection device clamping in the specified voltage range, which is2/7/2014 7:52 AM
Load dump protection: Old vs. new ISO standards EDN2 of p-protection--Old-.different from the standard waveform. The reason for this difference is the active voltage range ofthe clamping device in the load dump pulse, as shown in Figure 1. The device in Figure 2 isclamping at 101V Us, 1.75Ω Ri, and a 400ms pulse width.Figure 1 Input waveform of an ISO-16750-2 pulse: 5A, 79V U , 400ms pulse width conditionsFigure 2 Clamped waveform of the SM5S24A at an ISO-16750-2 pulse: 5A, 101V U , Ri s1.75Ω, 400ms pulse input conditionProtecting electronic devices from load dump by using a TVS diodeNow let's examine how to protect devices by clamping the voltage below the maximum inputvoltage for the voltage regulator or other electronic components in the circuit, without halting orpowering down the system. The protection device will not operate until the line voltage reaches24V for 1 to 10 minutes or longer in withstand test conditions.The clamping voltage of the load dump TVS device rises as the junction temperature changes2/7/2014 7:52 AM
Load dump protection: Old vs. new ISO standards EDN3 of p-protection--Old-.during continuous clamping operation. Figures 3 and 4 show the first and last clamping waves for10 pulses using TVS devices at Us 79V, Ri 1.0Ω, and 400ms pulse width at 1 minute intervalsbetween each pulse.Figure 3 First clamped waveform for SM5S24AFigure 4 Last clamped waveform for SM5S24AUsing the new test condition, 10 continuous pulses affected the surge suppressing capability ofthe load dump TVS, as shown in the following three graphs:2/7/2014 7:52 AM
Load dump protection: Old vs. new ISO standards EDN4 of p-protection--Old-.Figure 5 Capabilities of Vishay's SN5S24A under the new load dump test conditions. Suffix "M"lines are multiple pulses using the new test condition standards (ISO-16750-2). Suffix "S" linesare single pulses as defined by the old test condition standards (ISO-7637-2).These values are based on normal room temperature with the recommended pad size as listed inthe datasheet, but the actual capability varies by PCB type, pad size, and temperature conditions.AppendixEasy reference for load dump TVS vs. peak current (Amps)10 pulses in 10minutes (ms)Single pulse (ms)40ms100 220ms ms400ms40ms100ms220ms400msSM5S24A 7357463458523829SM6S24A 95655239656044352/7/2014 7:52 AM
Load dump protection: Old vs. new ISO standards EDN5 of 8SM8S24A Load-dump-protection--Old-.78696050Another way to select the correct load dump protection device is to refer to the maximumclamping current capability of the TVS and estimate the clamping current of the circuit based on:Circuit conditionRi 2ΩPeak voltage of alternator output in load dump 100VTarget clamping voltage 35VPulse width 200msPulse numbers 10 pulses in 10 minutesSM5S24A has 38A clamping capability in 10 pulses condition and its peak clamping current is32.5A ((100V - 35V) / 2Ω).ShareTweet0Like0Write a CommentTo commentplease Log In2/7/2014 7:52 AM
ISO-7637-2 standard and was used by major automotive component manufacturers worldwide. In 2010, this standard was replaced by a new automotive load dump test: ISO-16750-2. This article describes the changes to the load dump test condition and defines the maximum surge suppressing capability on an example load dump TVS under those conditions.