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SP489ECP Datasheet(PDF) 7 Page - Sipex Corporation |
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SP489ECP Datasheet(HTML) 7 Page - Sipex Corporation |
7 / 10 page 7 SP488E/489EDS/07 SP488E/489E Enhanced Quad RS-485/RS-422 Line Receivers © Copyright 2000 Sipex Corporation Figure 7. ESD Test Waveform for IEC1000-4-2 t=0ns t=30ns 0A 15A 30A t ¥ environment and human presence. The premise with IEC1000-4-2 is that the system is required to withstand an amount of static electricity when ESD is applied to points and surfaces of the equipment that are accessible to personnel during normal usage. The transceiver IC receives most of the ESD current when the ESD source is applied to the connector pins. The test circuit for IEC1000-4-2 is shown on Figure 6. There are two methods within IEC1000-4-2, the Air Discharge method and the Contact Discharge method. With the Air Discharge Method, an ESD voltage is applied to the equipment under test (EUT) through air. This simulates an electrically charged person ready to connect a cable onto the rear of the system only to find an unpleasant zap just before the person touches the back panel. The high energy potential on the person discharges through an arcing path to the rear panel of the system before he or she even touches the system. This energy, whether discharged directly or through air, is predominantly a function of the discharge current rather than the discharge voltage. Variables with an air discharge such as approach speed of the object carrying the ESD potential to the system and humidity will tend to change the discharge current. For example, the rise time of the discharge current varies with the approach speed. The Contact Discharge Method applies the ESD current directly to the EUT. This method was devised to reduce the unpredictability of the ESD arc. The discharge current rise time is constant since the energy is directly transferred without the air-gap arc. In situations such as hand held systems, the ESD charge can be directly discharged to the equipment from a person already holding the equipment. The current is transferred on to the keypad or the serial port of the equipment directly and then travels through the PCB and finally to the IC. The circuit model in Figures 5 and 6 represent the typical ESD testing circuit used for all three methods. The CS is initially charged with the DC power supply when the first switch (SW1) is on. Now that the capacitor is charged, the second switch (SW2) is on while SW1 switches off. The voltage stored in the capacitor is then applied through RS, the current limiting resistor, onto the device under test (DUT). In ESD tests, the SW2 switch is pulsed so that the device under test receives a duration of voltage. For the Human Body Model, the current limiting resistor (R S) and the source capacitor (CS) are 1.5kW an 100pF, respectively. For IEC-1000-4-2, the current limiting resistor (R S) and the source capacitor (C S) are 330W an 150pF, respectively. The higher C S value and lower R S value in the IEC1000-4-2 model are more stringent than the Human Body Model. The larger storage capacitor injects a higher voltage to the test point when SW2 is switched on. The lower current limiting resistor increases the current charge onto the test point. DEVICE PIN HUMAN BODY IEC1000-4-2 TESTED MODEL Air Discharge Direct Contact Level Driver Outputs +15kV +15kV +8kV 4 Receiver Inputs +15kV +15kV +8kV 4 Table 3. Transceiver ESD Tolerance Levels |
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