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SP310AET Datasheet(PDF) 5 Page - Sipex Corporation |
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SP310AET Datasheet(HTML) 5 Page - Sipex Corporation |
5 / 8 page SP231ADS/01 SP231A Enhanced RS-232 Line Drivers/Receivers © Copyright 2000 Sipex Corporation 5 R2 98 R IN R OUT 2 R1 12 13 R IN R OUT 1 T2 10 7 T IN 2 T OUT 2 T1 11 14 T IN 1 T OUT 1 15 GND 400k Ω 400k Ω 3 1 C + C - 1 1 6 16 V CC V+ + + 0.1 F 6.3V µ +5V to +10V Voltage Doubler +5V INPUT 2 V- 2 1 5k Ω 0.1 F 16V µ 5k Ω 5 4 C + C - 2 2 + 0.1 F 16V µ +10V to -10V Voltage Inverter 0.1 F 6.3V µ 10 F 6.3V µ SP232A + + * *The negative terminal of the V+ storage capacitor can be tied to either VCC or GND. Connecting the capacitor to VCC (+5V) is recommended. Figure 3. Typical Circuits using the SP231A and 232A. R2 65 R IN R OUT 2 R1 910 R IN R OUT 1 T2 7 4 T IN 2 T OUT 2 T1 8 11 T IN 1 T OUT 1 12 GND 400k Ω 400k Ω 2 1 C + C - 1 1 3 13 V CC V+ + + 0.1 F 6.3V µ +5V INPUT 14 V- 2 1 5k Ω 0.1 F 16V µ 5k Ω +12V to -12V Voltage Inverter SP231A V+ (+8.5V to +13.2V) Receivers The receivers convert RS-232 input signals to inverted TTL signals. Since the input is usually from a transmission line, where long cable lengths and system interference can degrade the signal, the inputs have a typical hysteresis margin of 500mV. This ensures that the receiver is virtually immune to noisy transmission lines. The input thresholds are 0.8V minimum and 2.4V maximum, again well within the ±3V RS-232 requirements. The receiver inputs are also protected against voltages up to ±30V. Should an input be left unconnected, a 5kOhm pulldown resistor to ground will commit the output of the receiver to a high state. In actual system applications, it is quite possible for signals to be applied to the receiver inputs before power is applied to the receiver circuitry. This occurs, for example, when a PC user attempts to print, only to realize the printer wasn’t turned on. In this case an RS-232 signal from the PC will appear on the receiver input at the printer. When the printer power is turned on, the receiver will operate normally. All of these enhanced devices are fully protected. Charge Pump The charge pump section of the these devices allows the circuit to operate from a single +5V ±10% power supply by generating the required operating voltages internal to the devices. The charge pump consists of two sections — 1) a voltage doubler and 2) a voltage inverter. As shown in Figure 1, an internal oscillator trig- gers the charge accumulation and voltage inver- sion. The voltage doubler momentarily stores a charge on capacitor C 1 equal to Vcc, referenced to ground. During the next transition of the oscillator this charge is boot-strapped to transfer charge to capacitor C 3. The voltage across C3 is now from V cc to V +. In the inverter section (Figure 2), the voltage across C 3 is transferred to C2 forcing a range of 0V to V+ across C 2. Boot-strapping of C2 will then transfer charge to C 4 to genrate V -. One of the significant enhancements over previous products of this type is that the values of the capacitors are no longer critical and have been decreased in size considerably to 0.1 µF. Because the charge pump runs at a much higher frequency, the 0.1 µF capacitors are sufficient to transfer and sustain charges to the two transmitters. APPLICATION HINTS Protection From Shorts to ±15V The driver outputs are protected against shorts to ground, other driver outputs, and V+ or V-. If the possibility exists that the outputs could be inadvertently connected to voltages higher than ±15V, then it is recommended that external protection be provided. For protection against voltages exceeding ±15V,twoback-to-backzener diodes connected from each output to ground will clamp the outputs to an acceptable voltage level. |
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