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SP302CS 数据表(PDF) 5 Page - Sipex Corporation |
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SP302CS 数据表(HTML) 5 Page - Sipex Corporation |
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5 / 18 page  55 Corporation SIGNAL PROCESSING EXCELLENCE Figure 1. Isolating SP301/302 From Ground; a) Single SP301/302; b) Multiple SP301/302 VDD GND VCC VEE 2N2222 VEE 3.3kΩ 3.3kΩ VDD GND VCC VEE Q3 Q4 SP301/302 SP301/302 VCC VDD Figure 2. Typical Circuit SOIC packages for operation over the commercial temperature range. VDD GND VCC VEE 2N2222 VEE VDD 3.3kΩ 3.3kΩ Q3 Q4 SP301/302 VCC a) b) circuitry. If the potential exists for momentary shorts to voltages greater than ±20V, it is recom- mended that a 220 Ω resistor be wired in series with each driver output. This will limit any damage from the higher short-circuit current from these higher voltage potentials. Voltage clamps such as back-to-back Zener diodes can be used to clamp the driver outputs to “safe” levels. Short circuit current to ground is inter- nally limited, and can therefore be sustained infinitely. Under normal operating conditions, the drivers can typically source 7mA at ±5V output, which exceeds the minimum RS-232 standards requirement. If an SP301/302 transmitter output occupies a data transmission line with other RS-232 de- vices which are not powered by the same power supplies, it is possible that a device that is not powered will have a low impedance path to ground at its driver output. The RS-232 stan- dards require that with no power applied to the device, the impedance from a transmitter output to ground must be greater than 300 Ω. This can be easily achieved as shown in Figure 1a, where an external transistor is used as a switch to USING THE SP301/302 POWER SUPPLIES The SP301/SP302 require ±12V and +5V for full RS-232 and RS-422 operation. The ±12V supplies set up the RS-232 ±9V voltage swings, and the +5V is used for the internal logic that formats the communications mode and controls the loopback function. The supply voltages can be decreased to as low as ±7V for V DD and VEE, and 4.0V for V CC. Under these supply condi- tions, derated performance can be expected. POWER SUPPLY SEQUENCING There are two requirements for power supply sequencing for the SP301/302. The first is that V DD is always greater than VCC. The second is that when the part is powered up, V DD must be applied 20ms before V CC. GENERAL USAGE RS232 Operation The SP301 and SP302 are fully compliant RS-232 devices. Their outputs are fully pro- tected against shorts to ±20V with no external RIB1 ROB1 TOB1 TIB1 RIA1 ROA1 TOA1 TIA1 SELECT A = 1 SELECT B = 0 LOOPBACK = 1 TOA2 RIA2 TOB2 TIB2 RIB2 ROB2 VDD GND VCC VEE 2N2222 VCC 3.3kΩ 3.3kΩ Q3 Q4 SP302 VEE VDD |
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