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ADM3485E Datasheet(PDF) 11 Page - Analog Devices |
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ADM3485E Datasheet(HTML) 11 Page - Analog Devices |
11 / 16 page ADM3485E Rev. D | Page 11 of 16 STANDARDS AND TESTING Table 6 compares RS-422 and RS-485 interface standards, and Table 7 and Table 8 show transmitting and receiving truth tables. Table 6. Specification RS-422 RS-485 Transmission Type Differential Differential Maximum Data Rate 10 Mbps 10 Mbps Maximum Cable Length 4000 ft 4000 ft Minimum Driver Output Voltage ±2 V ±1.5 V Driver Load Impedance 100 Ω 54 Ω Receiver Input Resistance 4 kΩ min 12 kΩ min Receiver Input Sensitivity ±200 mV ±200 mV Receiver Input Voltage Range −7 V to +7 V −7 V to +12 V Number of Drivers/Receivers per Line 1/10 32/32 Table 7. Transmitting Truth Table Transmitting Inputs Transmitting Outputs RE DE DI B A X1 1 1 0 1 X1 1 0 1 0 0 0 X1 High-Z2 High-Z2 1 0 X1 High-Z2 High-Z2 1 X = don't care. 2 High-Z = high impedance. Table 8. Receiving Truth Table Receiving Inputs Receiving Outputs RE DE A – B RO 0 X1 > +0.2 V 1 0 X1 < –0.2 V 0 0 X1 Inputs open 1 1 X1 X1 High-Z2 1 X = don't care. 2 High-Z = high impedance. ESD TESTING Two coupling methods are used for ESD testing, contact discharge and air-gap discharge. Contact discharge calls for a direct connection to the unit being tested. Air-gap discharge uses a higher test voltage but does not make direct contact with the unit under test. With air-gap discharge, the discharge gun is moved toward the unit under test, developing an arc across the air gap, hence the term air-gap discharge. This method is influenced by humidity, temperature, barometric pressure, distance, and rate of closure of the discharge gun. The contact discharge method, while less realistic, is more repeatable and is gaining acceptance and preference over the air-gap method. Although very little energy is contained within an ESD pulse, the extremely fast rise time, coupled with high voltages, can cause failures in unprotected semiconductors. Catastrophic destruction can occur immediately as a result of arcing or heating. Even if catastrophic failure does not occur immediately, the device can suffer from parametric degradation, which can result in degraded performance. The cumulative effects of continuous exposure can eventually lead to complete failure. I/O lines are particularly vulnerable to ESD damage. Simply touching or plugging in an I/O cable can result in a static discharge that can damage or completely destroy the interface product connected to the I/O port. It is extremely important, therefore, to have high levels of ESD protection on the I/O lines. The ESD discharge could induce latch-up in the device under test, so it is important that ESD testing on the I/O pins be carried out while device power is applied. This type of testing is more representative of a real-world I/O discharge, where the equipment is operating normally when the discharge occurs. Table 9. ESD Test Results ESD Test Method I/O Pins Human Body Model ±15 kV 100% 90% 36.8% 10% tRL tDL TIME t Figure 24. Human Body Model Current Waveform |
Similar Part No. - ADM3485E_15 |
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Similar Description - ADM3485E_15 |
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