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ISL32372EIVZ Fiches technique(PDF) 11 Page - Intersil Corporation |
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ISL32372EIVZ Fiches technique(HTML) 11 Page - Intersil Corporation |
11 / 20 page 11 FN6824.0 December 16, 2008 µcontrollers, and today most of these devices use power supplies significantly lower than 3.3V. Thus, the logic device’s low VOH might not exceed the VIH of a 3.3V or 5V powered DI or enable input. Connecting the VL pin to the power supply of the logic device (as shown in Figure 6) reduces the DI and enable input switching points to values compatible with the logic device’s output levels. Tailoring the logic pin input switching points to the supply voltage of the UART, ASIC, or µcontroller eliminates the need for a level shifter/translator between the two ICs. VL can be anywhere from VCC down to 1.5V, and Table 2 indicates typical VIH and VIL values for various VL settings so the user can ascertain whether or not a particular VL voltage meets his needs. Hot Plug Function When a piece of equipment powers up, there is a period of time where the processor or ASIC driving the RS-422 control lines (EN, EN, ENx) is unable to ensure that the RS-422 Tx outputs remain disabled. If the equipment is connected to the bus, a driver activating prematurely during power-up may drive invalid data on the bus. To avoid this scenario, this family incorporates a “Hot Plug” function. During power-up, circuitry monitoring VCC ensures that the Tx outputs remain disabled for a period of time, regardless of the state of the enable pins. This gives the processor/ASIC a chance to stabilize and drive the RS-422 control lines to the proper states. ESD Protection All pins on these devices include class 3 (>12kV) Human Body Model (HBM) ESD protection structures, but the RS-422 pins (driver outputs) incorporate advanced structures allowing them to survive ESD events in excess of ±15kV HBM, and ±16.5kV to IEC61000-4-2. The RS-422 pins are particularly vulnerable to ESD damage because they typically connect to an exposed port on the exterior of the finished product. Simply touching the port pins, or connecting a cable, can cause an ESD event that might destroy unprotected ICs. These new ESD structures protect the device whether or not it is powered up, and without degrading the RS-422 common mode range of -0.3V to +6V. This built-in ESD protection eliminates the need for board level protection structures (e.g., transient suppression diodes), and the associated, undesirable capacitive load they present. IEC61000-4-2 Testing The IEC61000 test method applies to finished equipment, rather than to an individual IC. Therefore, the pins most likely to suffer an ESD event are those that are exposed to the outside world (the RS-422 pins in this case), and the IC is tested in its typical application configuration (power applied) rather than testing each pin-to-pin combination. The IEC61000 standard’s lower current limiting resistor coupled with the larger charge storage capacitor yields a test that is much more severe than the HBM test. The extra ESD protection built into this device’s RS-422 pins allows the design of equipment meeting level 4 criteria without the need for additional board level protection on the RS-422 port. AIR-GAP DISCHARGE TEST METHOD For this test method, a charged probe tip moves toward the IC pin until the voltage arcs to it. The current waveform delivered to the IC pin depends on approach speed, humidity, temperature, etc., so it is difficult to obtain repeatable results. The RS-422 pins withstand ±16.5kV air-gap discharges. CONTACT DISCHARGE TEST METHOD During the contact discharge test, the probe contacts the tested pin before the probe tip is energized, thereby eliminating the variables associated with the air-gap TABLE 2. VIH AND VIL vs VL FOR VCC = 3.3V OR 5V VL (V) VIH (V) VIL (V) 1.6 0.7 0.45 2 0.85 0.6 2.3 1.1 0.75 2.7 1.4 (DI), 1.1 (ENs) 0.85 2.7 2 0.8 3.3 2.2 0.8 FIGURE 6. USING VL PIN TO ADJUST LOGIC LEVELS GND TXD DEN VCC = +2V UART/PROCESSOR GND DI EN VCC = +3.3V ISL32172E VOH ≤ 2 VIH ≥ 2 GND TXD DEN VCC = +2V UART/PROCESSOR GND DI EN VCC = +3.3V ISL32179E VOH ≤ 2 VIH = 0.85V VIH = 0.85V VL VOH ≤ 2 VIH ≥ 2 VOH ≤ 2 ISL32172E, ISL32272E, ISL32372E, ISL32174E, ISL32274E, ISL32374E, ISL32179E |
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Description similaire - ISL32372EIVZ |
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