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ISL3177EIUZ 数据表(PDF) 10 Page - Intersil Corporation |
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ISL3177EIUZ 数据表(HTML) 10 Page - Intersil Corporation |
10 / 19 page 10 FN6307.5 June 8, 2012 Application Information RS-485 and RS-422 are differential (balanced) data transmission standards for use in long haul or noisy environments. RS-422 is a subset of RS-485, so RS-485 transceivers are also RS-422 compliant. RS-422 is a point-to-multipoint (multidrop) standard, which allows only one driver and up to 10 (assuming one unit load devices) receivers on each bus. RS-485 is a true multipoint standard, which allows up to 32 one-unit load devices (any combination of drivers and receivers) on each bus. To allow for multipoint operation, the RS-485 spec requires that drivers must handle bus contention without sustaining any damage. Another important advantage of RS-485 is the extended common mode range (CMR), which specifies that the driver outputs and receiver inputs withstand signals that range from +12V to -7V. RS-422 and RS-485 are intended for runs as long as 4000’, so the wide CMR is necessary to handle ground potential differences, as well as voltages induced in the cable by external fields. Receiver Features These devices utilize a differential input receiver for maximum noise immunity and common mode rejection. Input sensitivity is better than ±200mV, as required by the RS-422 and RS-485 specifications. Receiver input resistance of 96k Ω surpasses the RS-422 spec of 4k Ω and is eight times the RS-485 “Unit Load (UL)” requirement of 12k Ω minimum. Thus, these products are known as “one-eighth UL” transceivers and there can be up to 256 of these devices on a network while still complying with the RS-485 loading specification. Receiver inputs function with common mode voltages as great as +9V/-7V outside the power supplies (i.e., +12V and -7V), making them ideal for long networks where induced voltages and ground potential differences are realistic concerns. All the receivers include a “Full Fail-Safe” function that guarantees a high level receiver output if the receiver inputs are unconnected (floating) or shorted. Fail-safe with shorted inputs is achieved by setting the Rx upper switching point to -50mV, thereby ensuring that the Rx sees 0V differential as a high input level. FIGURE 5A. TEST CIRCUIT FIGURE 5B. MEASUREMENT POINTS FIGURE 5. RECEIVER PROPAGATION DELAY FIGURE 6A. TEST CIRCUIT FIGURE 6B. MEASUREMENT POINTS FIGURE 6. RECEIVER ENABLE AND DISABLE TIMES (EXCEPT ISL3171E, ISL3174E, ISL3177E) Test Circuits and Waveforms (Continued) SIGNAL GENERATOR R RO RE A B GND 15pF RO +1.5V -1.5V tPLH 0V 0V VCC 0V 1.5V 1.5V tPHL A 1k Ω VCC GND SW PARAMETER DE A SW tHZ X +1.5V GND tLZ X -1.5V VCC tZH (Note 9) 0 +1.5V GND tZL (Note 9) 0 -1.5V VCC tZH(SHDN) (Note 12) 0 +1.5V GND tZL(SHDN) (Note 12) 0 -1.5V VCC SIGNAL GENERATOR R RO RE A B GND 15pF RO 3V 0V 1.5V 1.5V VOH 0V 1.5V VOH - 0.25V tHZ RO VCC VOL 1.5V VOL + 0.25V tLZ RE OUTPUT HIGH OUTPUT LOW tZL, tZL(SHDN) tZH, tZH(SHDN) NOTE 10 NOTE 10 NOTE 10 ISL3170E, ISL3171E, ISL3172E, ISL3173E, ISL3174E, ISL3175E,ISL3176E, ISL3177E, ISL3178E |
类似零件编号 - ISL3177EIUZ |
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类似说明 - ISL3177EIUZ |
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