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ADM1181A Scheda tecnica(PDF) 4 Page - Analog Devices |
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ADM1181A Scheda tecnica(HTML) 4 Page - Analog Devices |
4 / 12 page ADM202E/ADM1181A –4– REV. 0 GENERAL DESCRIPTION The ADM202E/ADM1181E are ruggedized 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 compatibility with the EU directive on Electromag- netic 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 up to ±15 kV and Electrical Fast Transients up to ±2 kV. This ensures compliance to IE1000-4-2 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 keep the power dissipation to an absolute minimum allowing maximum battery life in portable applications. The ADM202E/ADM1181A is a modification, enhancement and improvement to the AD230–AD241 family and its deriva- tives. It is essentially plug-in compatible and does not have ma- terially different applications. CIRCUIT DESCRIPTION The internal circuitry consists of four main sections. These are: 1. A charge pump voltage converter 2. 5 V logic to EIA-232 transmitters 3. EIA-232 to 5 V logic receivers. 4. Transient protection circuit on all I/O lines Charge Pump DC-DC Voltage Converter The charge pump voltage converter consists of an 200 kHz os- cillator and a switching matrix. The converter generates a ±10 V supply from the input +5 V level. This is done in two stages us- ing a switched capacitor technique as illustrated below. 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. Capacitors C3 and 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, while 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 capaci- tors (up to 47 µF) can be used for capacitors C1–C4. This facili- tates 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 1. Charge Pump Voltage Doubler S1 S2 C2 S4 S3 C4 V– = –(V+) V+ GND INTERNAL OSCILLATOR GND FROM VOLTAGE DOUBLER Figure 2. Charge Pump Voltage Inverter Transmitter (Driver) Section The drivers convert 5 V logic input levels into RS-232 output levels. With VCC = +5 V and driving an RS-232 load, the output voltage swing is typically ±9 V. Receiver Section The receivers are inverting level shifters which accept RS-232 input levels and translate them into 5 V logic output levels. The inputs have internal 5 k Ω pull-down resistors to ground and are also protected against overvoltages of up to ±30 V. Un- connected inputs are pulled to 0 V by the internal 5 k Ω pull- down resistor. This, therefore, results in a Logic 1 output level for unconnected inputs or for inputs connected to GND. The receivers have Schmitt trigger inputs with a hysteresis level of 0.5 V. This ensures error-free reception for both noisy inputs and for inputs with slow transition times. |
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