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ISL32272EFVZ Fiches technique(PDF) 10 Page - Intersil Corporation |
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ISL32272EFVZ Fiches technique(HTML) 10 Page - Intersil Corporation |
10 / 20 page 10 FN6824.0 December 16, 2008 Application Information RS-422 is a differential (balanced) data transmission standard for use in long haul or noisy environments. 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. Driver Features These RS-422 drivers are differential output devices that deliver at least 2V across a 100 Ω load. The drivers feature low propagation delay skew to maximize bit width, and to minimize EMI. The 460kbps driver outputs are slew rate limited to minimize EMI, and to reduce reflections in unterminated or improperly terminated networks. Outputs of the 10Mbps and 32Mbps drivers are not limited, so faster output transition times allow the higher data rates. Driver Enable Functions All product types include functionality to allow disabling of the Tx outputs. The ISL32x72E types feature group (all four Tx) enable functions that are active high (EN) or active low (EN). Drivers enable when EN = 1, or when EN = 0, and they disable only when EN = 0 and EN = 1. ISL32x74E versions use active high paired enable functions (EN12 and EN34) that enable (when high) or disable (when low) the corresponding pairs of Tx. All four of these enable pins have internal pull-up resistors to VCC, but unused enable pins that need to be high (e.g., EN when using the EN input for enable control, or EN12 and EN34 when using always enabled drivers) should always be connected externally to VCC. If VCC transients might exceed 7V, then inserting a series resistor between the input(s) and VCC limits the current that will flow if the input’s ESD protection starts conducting. The ISL32179E has the most flexible enable scheme. Its six enable pins allow for group, paired, or individual channel enable control. Figure 5 details the ISL32179E’s internal enable logic. To utilize a group enable function, connect all the ENx pins high, and handle the EN and EN pins as described in the previous paragraph. For paired enables, connect EN and EN high (for the lowest current in SHDN mode, if SHDN is used) and tie EN1 and EN2 together, and EN3 and EN4 together. For individual channel enables, again connect EN and EN high, and drive the appropriate ENX (active high) for the particular channel. All of the enable pins incorporate pull-up resistors to VCC, but unused enable pins of any type should be externally connected high, rather than being left floating. Connecting to VCC is the best choice, but VL may be utilized as long as SHDN power isn’t a primary concern (for each VL connected input, ICC increases by ((VCC - VL)/600kΩ). If VCC or VL transients might exceed 7V, then inserting a series resistor between the input(s) and the supply limits the current that will flow if the input’s ESD protection starts conducting. Wide Supply Range These ICs are designed to operate with a wide range of supply voltages from 3.0V to 5.5V, and they meet the RS-422 specifications for that full supply voltage range. 5.5V TOLERANT LOGIC PINS Logic input pins (driver inputs, enables, SHDNEN) 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. Input voltages up to 7V are easily tolerated. Logic Supply (VL Pin, ISL32179E Only) Note: Power-up VCC before powering up the VL supply. If unused enable pins are connected to VL rather than to VCC, then a small ICC ((VCC - VL)/600kΩ) will flow due to the internal pull-up resistor connecting to VCC. The ISL32179E includes a VL pin that powers the logic inputs (driver inputs, enables, SHDNEN). These pins interface with “logic” devices such as UARTs, ASICs, and FIGURE 4A. TEST CIRCUIT FIGURE 4B. MEASUREMENT POINTS FIGURE 4. DRIVER DATA RATE Test Circuits and Waveforms (Continued) D EN DI VCC OR VL SIGNAL GENERATOR Z Y CD VOD + - 100 Ω LOWER OF VCC OR VL 0V DIFF OUT (Y - Z) +VOD -VOD DI 0V FIGURE 5. ISL32179E ENABLE LOGIC 1 OF 4 CHANNELS VCC VCC VCC ENX EN EN CHX EN ISL32172E, ISL32272E, ISL32372E, ISL32174E, ISL32274E, ISL32374E, ISL32179E |
Numéro de pièce similaire - ISL32272EFVZ |
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Description similaire - ISL32272EFVZ |
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