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Formerly a Division of Motorola
I2t Test Results Summary Device: MR2504 Button Package Date: 11/20/99 Objective: Identify a low cost diode that can withstand greater than 1000 A for greater than 3 sec without failing open. The purpose of the diode is to be part of a reverse battery protection device that consists of a diode and fuse such that the fuse normally conducts all automotive load currents including cranking current, and the diode normally only blocks. But during reverse battery condition, the diode conducts the short circuit current through the fuse until the fuse blows electrically, separating the battery from the automobile circuitry. Test Description: The diode was clamped between brass bar electrical contacts with a slight pressure to prevent it from opening. The brass bars provided some heat sinking, however we believe that since some tests resulted in I2t values nearly 4x the requirement, that the heat sinking is not a requirement. In every case, the diode shorted, the solder reflowed, and the plastic cracked. While the diodes were mechanically held together to avoid separation upon plastic failure, they were held with the die mounting plane vertical such that if the solder were going to flow out of the device it could, but it apparently did not. As the test set up had no fuse to determine the end of test time, test times were left to the technician’s discretion (smoke from the battery, and temperature of wires being dominant factors). Since the diodes never opened, it was not possible to determine the fusing current of the device if it is held immobile during the test. The set up consisted of 2AWG battery cables, a shunt resistor for measuring current, brass connectors and a clamp (bench vise). See schematic of test set up. 1. 2352 amps for 1 second. I2t = 5.53 x 106. See Figure 1. Diode shorted.
2. Diode test at 2400 amps. Diode shorted at 498mS. Voltage drop = 1.28V. See Figure 2. In this test, the time scale of the oscilloscope was set to capture the wave form of the diode failure, and not the entire test, so total test duration is not known. 3. 2304 amps for 2 seconds. I2t =10.62 x 106. Diode shorted. 4. 2112 amps for 1.55 seconds. I2t = 6.91 x 106. Diode shorted. 5. 2064 amps for 2.8 seconds. I2t = 11.93 x 106. Diode shorted at 300mS. Voltage drop = 800-1000mV. See Figure 3. You may notice that test 2 and 5 captured the diode drop and time to failure, and they are significantly different I2t values (2.87 x 106 in test 2 and 1.28 x 106 in test 5). Also the energy levels are likewise
different (1530J in test 2 and 495J in test 5). This may have an impact on the effectiveness of the proposal for protection, but I2t is not usually a critical design parameter for diodes. In light of the previous requirement that the diode not fail open for at least 3 seconds at current levels a little higher than 1000 Amps, it appears this diode will work for future evaluations, and may be suitable for use in the final design. Jarvis Carter Mike Schager
Figure 1 1 second at (392 mv *6) or 2352 amps
Figure 2 2400 amps
Figure 3 344mv*6 = 2064 amps for 2.8192 seconds