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ADM3232E датащи(PDF) 8 Page - Analog Devices |
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ADM3232E датащи(HTML) 8 Page - Analog Devices |
8 / 12 page ADM3232E Rev. B | Page 8 of 12 THEORY OF OPERATION The ADM3232E is a single-channel RS-232 line driver/receiver. Step-up voltage converters, coupled with level-shifting transmitters and receivers, allow RS-232 levels to be developed while operating from a single 3.3 V supply. CMOS technology is used to keep the power dissipation to an absolute minimum, allowing maximum battery life in portable applications. CIRCUIT DESCRIPTION The internal circuitry consists of the following main sections: • A charge pump voltage converter • A 3.3 V logic to RS-232 transmitter • An RS-232 to 3.3 V logic receiver Charge Pump Voltage Converter The charge pump voltage converter consists of a 200 kHz oscillator and a switching matrix. The converter generates a ±6.6 V supply from the input 3.3 V level. This is accomplished in two stages by using a switched capacitor technique as shown in Figure 10. First, the 3.3 V input supply is doubled to 6.6 V by using Capacitor C1 as the charge storage element. The +6.6 V level is then inverted to generate −6.6 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. Capacitor C3 is shown connected between V+ and VCC. It is also acceptable to connect this capacitor between V+ and GND. If desired, larger capacitors (up to 10 μF) can be used for Capacitor C1 to Capacitor C4. C1+ C2+ C1– C2– VCC V– V+ T1IN T1OUT T2IN T2OUT R1OUT R1IN R2OUT R2IN TTL/CMOS INPUTS RS-232 OUTPUTS TTL/CMOS OUTPUTS RS-232 INPUTS* T1 T2 R1 R2 + + C1 0.1µF 10V C2 0.1µF 10V GND ADM3232E C3 0.1µF 6.3V +3.3V INPUT +3.3V TO +6.6V VOLTAGE DOUBLER +6.6V TO –6.6V VOLTAGE INVERTER C5 0.1µF C4 0.1µF 10V *INTERNAL 5kΩ PULL-DOWN RESISTOR ON EACH RS-232 INPUT. 5kΩ 5kΩ Figure 10. Typical Operating Circuit C1 + C3 + S3 S4 S1 S2 INTERNAL OSCILLATOR VCC GND VCC V+ = 2VCC Figure 11. Charge Pump Voltage Doubler C2 + C4 + S3 S4 S1 S2 INTERNAL OSCILLATOR V+ GND V– = –(V+) GND FROM VOLTAGE DOUBLER Figure 12. Charge Pump Voltage Inverter 3.3 V Logic to RS-232 Transmitter The drivers convert 3.3 V logic input levels into RS-232 output levels. With VCC = 3.3 V and driving an RS-232 load, the output voltage swing is typically ±6 V. RS-232 to 3.3 V Logic Receiver The receivers are inverting level shifters that accept RS-232 input levels and translate them into 3 V logic output levels. The inputs have internal 5 kΩ pull-down resistors to ground and are pro- tected against overvoltages up to ±30 V. Unconnected inputs are pulled to 0 V by the internal 5 kΩ pull-down resistor. This 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 0.4 V. This ensures error-free reception for both noisy inputs and for inputs with slow transition times. ESD Protection on RS-232 Pins All RS-232 (TxOUT and RxIN) inputs and outputs are protected against electrostatic discharges (up to ±15 kV). This ensures compliance with IEC 1000-4-2 requirements. HIGH BAUD RATE The ADM3232E features high slew rates, permitting data trans- mission at rates well in excess of the EIA-232E specifications. RS-232 voltage levels are maintained at data rates up to 460 kbps, even under worst-case loading conditions. The slew rate is internally controlled to less than 30 V/μs to minimize EMI interference. |
Аналогичный номер детали - ADM3232E_15 |
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Аналогичное описание - ADM3232E_15 |
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