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ADM208EAR-REEL Datasheet(PDF) 11 Page - Analog Devices |
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ADM208EAR-REEL Datasheet(HTML) 11 Page - Analog Devices |
11 / 20 page ADM206E/ADM207E/ADM208E/ADM211E/ADM213E Rev. E | Page 11 of 20 On the ADM213E, Receiver R4 and Receiver R5 remain enabled in shutdown. Note that the transmitters are disabled but are not tristated in shutdown; it is not permitted to connect multiple (RS-232) driver outputs together. The shutdown feature is very useful in battery-operated systems since it reduces the power consumption to 1 μW. During shutdown, the charge pump is also disabled. The shutdown control input is active high on the ADM211E, and it is active low on the ADM213E. When exiting shutdown, the charge pump is restarted, and it takes approximately 100 μs for it to reach its steady state operating condition. HIGH BAUD RATE The ADM2xxE feature high slew rates, permitting data transmission rates well in excess of the EIA-232-E specifications. RS-232 levels are maintained at data rates up to 230 kbps, even under worst-case loading conditions. This allows for high speed data links between two terminals, making it suitable for the new generation modem standards that require data rates of 200 kbps. The slew rate is controlled internally to less than 30 V/μs to minimize EMI interference. tDR 3V 0V EN INPUT RECEIVER OUTPUT NOTES 1. EN IS THE COMPLEMENT OF EN FOR THE ADM213E. VOH VOL VOH –0.1V VOL +0.1V Figure 22. Receiver Disable Timing tER 3V 0V EN INPUT RECEIVER OUTPUT +3.5V +0.8V NOTES 1. EN IS THE COMPLEMENT OF EN FOR THE ADM213E. Figure 23. Receiver Enable Timing ESD/EFT TRANSIENT PROTECTION SCHEME The ADM2xxE use protective clamping structures on all inputs and outputs that clamp the voltage to a safe level and dissipate the energy present in ESD (electrostatic) and EFT (electrical fast transient) discharges. A simplified schematic of the protection structure is shown in Figure 24 and Figure 25. Each input and output contains two back-to-back high speed clamping diodes. During normal operation, with maximum RS232 signal levels, the diodes have no effect because one or the other is reverse biased, depending on the polarity of the signal. If, however, the voltage exceeds about ±50 V, reverse breakdown occurs, and the voltage is clamped at this level. The diodes are large p-n junctions designed to handle the instantaneous current surges that can exceed several amperes. The transmitter outputs and receiver inputs have a similar protection structure. The receiver inputs can also dissipate some of the energy through the internal 5 kΩ 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 discussed in the ESD Testing (IEC 100042) and EFT/Burst Testing (IEC 100044) sections. RIN RX D1 D2 R1 RECEIVER INPUT Figure 24. Receiver Input Protection Scheme TOUT RX D1 D2 TRANSMITTER OUTPUT Figure 25. Transmitter Output Protection Scheme ESD TESTING (IEC 1000-4-2) IEC 1000-4-2 (previously IEC 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-gap discharge, the discharge gun is moved toward the unit under test, developing an arc across the air gap. 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 |
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