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ISL3295EIHZ-T データシート(PDF) 10 Page - Intersil Corporation |
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ISL3295EIHZ-T データシート(HTML) 10 Page - Intersil Corporation |
10 / 17 page 10 FN6544.0 September 19, 2007 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 transmitters and receivers 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 specification 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. Driver Features These RS-485/RS-422 drivers are differential output devices that delivers at least 1.5V across a 54 Ω load (RS-485), and at least 2V across a 100 Ω load (RS-422). The drivers feature low propagation delay skew to maximize bit width, and to minimize EMI. All drivers are tri-statable via the active high DE input. If the Tx enable function isn’t needed, tie DE to VCC (or VL) through a 1k Ω to 3kΩ resistor. The 250kbps and 500kbps driver outputs are slew rate limited to minimize EMI, and to reduce reflections in unterminated or improperly terminated networks. Outputs of the ISL3295E and ISL3298E drivers are not limited, so faster output transition times allow data rates of at least 20Mbps. Wide Supply Range The ISL3293E through ISL3298E are optimized for 3.3V operation, but can be operated with supply voltages as high as 5.5V. These devices meet the RS-422 and RS-485 specifications for supply voltages less than 4V, and are RS-422 and RS-485 compatible for supplies greater than 4V. Operation at +125°C requires VCC ≤ 3.6V, while 5V operation requires adding output current limiting resistors (as described in the “Driver Overload Protection” on page 11) if output short circuits (e.g., from bus contention) are a possibility. 5.5V Tolerant Logic Pins Logic input pins (DI, DE) contain no ESD nor parasitic diodes to VCC (nor to VL), so they withstand input voltages exceeding 5.5V regardless of the VCC and VL voltages. Logic Supply (VL Pin, ISL3296E through ISL3298E) Note: Power-up VCC before powering up the VL supply. The ISL3296E through ISL3298E include a VL pin that powers the logic inputs (DI and DE). These pins interface with “logic” devices such as UARTs, ASICs, and µcontrollers, and today most of these devices use power supplies significantly lower than 3.3V. Thus, the logic device’s low VOH might not exceed the VIH of a 3.3V or 5V powered DI or DE input. Connecting the VL pin to the power supply of the logic device (as shown in Figure 5) reduces the DI and DE input switching points to values compatible with the logic device’s output levels. Tailoring the logic pin input switching points and output levels to the supply voltage of the UART, ASIC, or µcontroller eliminates the need for a level shifter/translator between the two ICs. VL can be anywhere from VCC down to 1.35V, but the input switching points may not provide enough noise margin, and 20Mbps data rates may not be achievable, when VL <1.5V. Table 2 indicates typical VIH and VIL values for various VL settings so the user can ascertain whether or not a particular VL voltage meets his needs. FIGURE 5. USING VL PIN TO ADJUST LOGIC LEVELS GND TXD DEN VCC = +2V UART/PROCESSOR GND DI DE VCC = +3.3V ISL3293E VOH ≤ 2V VIH ≥ 2V GND TXD DEN VCC = +2V UART/PROCESSOR GND DI DE VCC = +3.3V ISL3296E VOH ≤ 2V VIH = 1.4V VIH = 1.4V VL VOH ≤ 2V VIH ≥ 2V VOH ≤ 2V ISL3293E, ISL3294E, ISL3295E, ISL3296E, ISL3297E, ISL3298E |
同様の部品番号 - ISL3295EIHZ-T |
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同様の説明 - ISL3295EIHZ-T |
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