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ADM207EAN Arkusz danych(PDF) 10 Page - Analog Devices |
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ADM207EAN Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 16 page ADM206E/ADM207E/ADM208E/ADM211E/ADM213E REV. B –10– new generation modem standards which requires data rates of 200 kb/s. The slew rate is internally controlled to less than 30 V/ µs in order to minimize EMI interference. tDR 3V 0V EN INPUT VOH VOL RECEIVER OUTPUT VOH –0.1V VOL +0.1V NOTE: EN IS THE COMPLEMENT OF EN FOR THE ADM213E Figure 22. Receiver-Disable Timing tER 3V 0V EN INPUT RECEIVER OUTPUT +3.5V +0.8V NOTE: EN IS THE COMPLEMENT OF EN FOR THE ADM213E Figure 23. Receiver Enable Timing ESD/EFT Transient Protection Scheme The ADM2xxE uses protective clamping structures on all inputs and outputs which clamps the voltage to a safe level and dissi- pates the energy present in ESD (Electrostatic) and EFT (Elec- trical Fast Transients) discharges. A simplified schematic of the protection structure is shown in Figures 24a and 24b. Each input and output contains two back-to-back high speed clamp- ing diodes. During normal operation with maximum RS-232 signal levels, the diodes have no affect as one or the other is reverse biased depending on the polarity of the signal. If how- ever the voltage exceeds about ±50 V, reverse breakdown occurs and the voltage is clamped at this level. The diodes are large p-n junctions which are designed to handle the instantaneous cur- rent surge which can exceed several amperes. The transmitter outputs and receiver inputs have a similar pro- tection structure. The receiver inputs can also dissipate some of the energy through the internal 5 k Ω resistor to GND as well as through the protection diodes. The protection structure achieves ESD protection up to ±15 kV and EFT protection up to ±2 kV on all RS-232 I-O lines. The methods used to test the protection scheme are dis- cussed later. RIN RX D1 D2 RECEIVER INPUT R1 Figure 24a. Receiver Input Protection Scheme RX D1 D2 TRANSMITTER OUTPUT TOUT Figure 24b. Transmitter Output Protection Scheme ESD TESTING (IEC1000-4-2) IEC1000-4-2 (previously 801-2) specifies compliance testing using two coupling methods, 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 discharge, the discharge gun is moved towards the unit un- der test developing an arc across the air gap, hence the term air- 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 in preference to 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 destruc- tion can occur immediately as a result of arcing or heating. Even if catastrophic failure does not occur immediately, the device may suffer from parametric degradation which may 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 dis- charge that can damage or completely destroy the interface product connected to the I-O port. Traditional ESD test meth- ods such as the MIL-STD-883B method 3015.7 do not fully test a products susceptibility to this type of discharge. This test was intended to test a products susceptibility to ESD damage during handling. Each pin is tested with respect to all other pins. There are some important differences between the tradi- tional test and the IEC test: (a) The IEC test is much more stringent in terms of discharge ( energy. The peak current injected is over four times greater. (b) The current rise time is significantly faster in the IEC test. (c) The IEC test is carried out while power is applied to the device. It is possible that the ESD discharge could induce latch-up in the device under test. This test therefore is more representative of a real-world I-O discharge where the equipment is operating nor- mally with power applied. For maximum peace of mind however, both tests should be performed, therefore, ensuring maximum protection both during handling and later during field service. |
Podobny numer części - ADM207EAN |
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Podobny opis - ADM207EAN |
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