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ADUM1100ARWZ Datasheet(PDF) 2 Page - Analog Devices |
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ADUM1100ARWZ Datasheet(HTML) 2 Page - Analog Devices |
2 / 8 page –2– AN-793 –3– AN-793 Table I summarizes the ESD test results for the ADuM140x quad isolator. One might conclude from Table I that iCouplers can only be used in systems with ESD ratings of < 4 kV. In reality it is quite common for iCouplers to be used in systems that pass 15 kV ESD levels per IEC 61000-4-2. The difference is in the test methods: The component-level tests call for direct application of ESD events to the pins or body of an unpowered device, while system-level tests call for application ESD events to various locations in the system accessible to external ESD occurrences. Furthermore, the specific waveforms used in component-level and system-level testing differ. Table I. ADuM140x ESD Test Results ESD First Pass First Fail Model Voltage (V) Voltage (V) Human Body Model 3,500 4,000 Field Induced Charge Device Model 1,500 2,000 Machine Model 200 400 For complete information on Analog Devices ESD testing, refer to the Analog Devices Reliability Handbook. To accurately predict the performance of iCouplers in a system, the designer needs to understand the nature of the system tests and weigh how they impact the iCoupler at the component level. Table II lists common system-level tests used in iCoupler applications. Several examples of these tests will be discussed later. Table II. Common System Tests Used in iCoupler Applications Test Test Standard Purpose Voltage (V rms)1 IEC 61000-4-2 ESD 2,000 to 15,000 IEC 61000-4-4 FastTransient/Burst 500 to 4,000 IEC 61000-4-5 Surge 500 to 4,000 1IEC 61000-4 tests include compliance levels; the test voltages shown are the ranges for level 1 (lowest) through level 4 (highest) compliance. iCoupler Model for Analyzing SystemTest Performance Figure 2 shows a circuit model of an iCoupler which is useful to understand the impact of system-level testing. Inductors L1, L2, L3, and L4 are due largely to package pins and bond wires, while capacitor C1 is due to the stray capacitance across the isolation barrier. The induc- tance values are approximately 0.2 nH. The capacitance value is approximately 0.3 pF per iCoupler channel. L1 VDD1 VIN GND1 VDD2 VO GND2 L3 C1 L2 L4 Figure 2. iCoupler Model Useful in Analyzing System Designs Latch-Up in CMOS Devices Inherent in a CMOS process are parasitic PNP and NPN transistors configured as silicon control rectifiers (SCR). Latch-up is a condition that comes about when this parasitic SCR is triggered. This causes a low resis- tance to appear from VDD to ground, and a subsequent large current to be drawn through the device. This excessive current lays open the possibility of damage due to EOS. Damage caused by latch-up can range from complete destruction of the device to parametric degradation. More insidious are latent failures that could affect operation later in a system’s lifetime. An excellent treatise on the subject of latch-up in general can be found in the Analog Dialogue 35- 05 (2001) article, “Winning the Battle Against Latch-Up in CMOS Switches.” While this article specifically addresses problems with CMOS switches, it is generally applicable to all CMOS devices, including iCouplers. The use of ceramic bypass capacitors to minimize supply noise between VDD and ground is highly recommended in all iCoupler applications. These should have a value between 0.01 F and 0.1 F and be placed as close as possible to the iCoupler device. Even with adequate bypassing, latch-up problems may still occur in some applications. Placing a 200 resistor in series with VDD is also helpful. This limits the supply current to 25 mA in 5 V applications, which is below the latch-up trigger current. However, depending on the supply current being drawn, this series resistance can reduce the supply voltage at the iCoupler to an unacceptable level. This is most likely to be a concern when operating at high data rates that involve high supply currents. Usually the mechanism that causes latch-up is an over- voltage condition beyond the part’s absolute maximum rating (>7.0 V or <–0.5 V for most iCoupler products). Once an iCoupler is integrated into a system the source of the overvoltage is not always clear. However, it is usually manageable once understood. REV. 0 REV. 0 |
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