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ADM202EARN-REEL Arkusz danych(PDF) 6 Page - Analog Devices |
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ADM202EARN-REEL Arkusz danych(HTML) 6 Page - Analog Devices |
6 / 16 page ADM202E/ADM1181A Rev. C | Page 6 of 16 GENERAL DESCRIPTION The ADM202E/ADM1181E are rugged RS-232 line drivers/receivers. Step-up voltage converters coupled with level- shifting transmitters and receivers allow RS-232 levels to be developed while operating from a single 5 V supply. Features include low power consumption, high transmission rates, and compliance with the EU directive on electromagnetic compatibility. EM compatibility includes protection against radiated and conducted interference, including high levels of electrostatic discharge. All inputs and outputs contain protection against electrostatic discharges of up to ±15 kV and electrical fast transients of up to ±2 kV. This ensures compliance to IEC1000-4-2 and IEC1000-4-4 requirements. The devices are ideally suited for operation in electrically harsh environments or where RS-232 cables are frequently being plugged/unplugged. They are also immune to high RF field strengths without special shielding precautions. CMOS technology is used to minimize the power dissipation, allowing maximum battery life in portable applications. The ADM202E/ADM1181A serve as a modification, enhancement, and improvement to the ADM230–ADM241 family and its derivatives. It is essentially plug-in compatible and do not have materially different applications. CIRCUIT DESCRIPTION The internal circuitry consists of four main sections: • A charge-pump voltage converter • 5 V logic to EIA-232 transmitters • EIA-232 to 5 V logic receivers. • Transient protection circuit on all I/O lines Charge-Pump DC-to-DC Voltage Converter The charge-pump voltage converter consists of a 200 kHz oscillator and a switching matrix. The converter generates a ±10 V supply from the input 5 V level. This is done in two stages, using a switched capacitor technique, as illustrated in Figure 6 and Figure 7. First, the 5 V input supply is doubled to 10 V, using Capacitor C1 as the charge storage element. The 10 V level is then inverted to generate −10 V, using C2 as the storage element. Capacitor C3 and Capacitor C4 are used to reduce the output ripple. Their values are not critical and can be increased if desired. On the ADM202E, Capacitor C3 is shown connected between V+ and VCC, whereas it is connected between V+ and GND on the ADM1181A. It is acceptable to use either configuration with both the ADM202E and ADM1181A. If desired, larger capacitors (up to 47 µF) can be used for Capacitor C1 to Capacitor C4. This facilitates direct substitution with older generation charge-pump RS-232 transceivers. S1 S2 C1 S4 S3 C3 V+ = 2VCC VCC VCC GND INTERNAL OSCILLATOR NOTE: C3 CONNECTS BETWEEN V+ AND GND ON THE ADM1181A Figure 6. Charge-Pump Voltage Doubler S1 S2 C2 S4 S3 C4 V– = –(V+) V+ GND INTERNAL OSCILLATOR GND FROM VOLTAGE DOUBLER Figure 7. Charge-Pump Voltage Inverter Transmitter (Driver) Section The drivers convert 5 V logic input levels into RS-232 output levels. When driving an RS-232 load with VCC = 5 V, the output voltage swing is typically ±9 V. Receiver Section The receivers are inverting level shifters that accept RS-232 input levels and translate them into 5 V logic output levels. The inputs have internal 5 kΩ pull-down resistors to ground and are also protected against overvoltages of up to ±30 V. Unconnected inputs are pulled to 0 V by the internal 5 kΩ pull-down resistor. Therefore, unconnected inputs and those connected to GND have a Logic 1 output level. The receivers have Schmitt-trigger inputs with a hysteresis level of 0.65 V. This ensures error-free reception for both noisy inputs and inputs with slow transition times. HIGH BAUD RATE The ADM202E/ADM1181A feature high slew rates, permitting data transmission at rates well in excess of the EIA/RS-232-E specifications. RS-232 voltage levels are maintained at data rates of up to 230 kbps, even under worst case loading conditions. This allows for high speed data links between two terminals and is also suitable for the new generation ISDN modem standards, which require data rates of 230 kbps. The slew rate is internally controlled to less than 30 V/µs to minimize EMI interference. |
Podobny numer części - ADM202EARN-REEL |
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Podobny opis - ADM202EARN-REEL |
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