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ISL4223EIR Datasheet(PDF) 6 Page - Intersil Corporation |
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ISL4223EIR Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 13 page 6 and V- supplies are pumped up to the nominal values), resulting in significant power savings. Transmitters The transmitters are proprietary, low dropout, inverting drivers that translate TTL/CMOS inputs to EIA/TIA-232 output levels. Coupled with the on-chip ±5.5V supplies, these transmitters deliver true RS-232 levels over a wide range of single supply system voltages. All transmitter outputs disable and assume a high impedance state when the device enters the powerdown mode (see Table 2). These outputs may be driven to ±12V when disabled. The devices guarantee a 250kBps data rate for full load conditions (3k Ω and 1000pF), VCC ≥ 3.0V, with one transmitter operating at full speed. Under more typical conditions of VCC ≥ 3.3V, RL = 3kΩ, and CL = 250pF, one transmitter easily operates at 900kBps. Transmitter inputs float if left unconnected, and may cause ICC increases. Connect unused inputs to GND for the best performance. Receivers All the ISL422XE devices contain standard inverting receivers that three-state via the EN control line. All the receivers convert RS-232 signals to CMOS output levels and accept inputs up to ±25V while presenting the required 3kΩ to 7k Ω input impedance (see Figure 1) even if the power is off (VCC = 0V). The receivers’ Schmitt trigger input stage uses hysteresis to increase noise immunity and decrease errors due to slow input signal transitions. Receivers driving a powered down UART must be disabled to prevent current flow through, and possible damage to, the UART’s protection diodes (see Figures 2 and 3). This can be accomplished on the ISL422XE by driving the EN input high whenever the UART powers down. Figure 3 also shows that the INVALID output can be used to determine when the UART should be powered down. When the RS-232 cable is disconnected, INVALID switches low indicating that the UART is no longer needed. Reconnecting the cable drives INVALID back high, indicating that the UART should be powered up. Low Power Operation These 3V devices require a nominal supply current of 0.3mA, even at VCC = 5.5V, during normal operation (not in powerdown mode). This is considerably less than the 5mA to 11mA current required by comparable 5V RS-232 devices, allowing users to reduce system power simply by switching to this new family. Powerdown Functionality The already low current requirement drops significantly when the device enters powerdown mode. In powerdown, supply current drops to 150nA, because the on-chip charge pump turns off (V+ collapses to VCC, V- collapses to GND), and the transmitter outputs three-state. Receiver outputs are unaffected by powerdown; refer to Table 2 for details. This micro-power mode makes the ISL422XE ideal for battery powered and portable applications. Software Controlled (Manual) Powerdown The ISL422XE family provides pins that allow the user to force the IC into the low power, standby state. The ISL422XE utilize a two pin approach where the FORCEON and FORCEOFF inputs determine the IC’s RXOUT GND ≤ VROUT ≤ VCC 5k Ω RXIN -25V ≤ VRIN ≤ +25V GND VCC FIGURE 1. INVERTING RECEIVER CONNECTIONS FIGURE 2. POWER DRAIN THROUGH POWERED DOWN PERIPHERAL OLD VCC POWERED GND SHDN = GND VCC Rx Tx VCC CURRENT VOUT = VCC FLOW RS-232 CHIP DOWN UART FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN ISL422XE TRANSITION RX TX INVALID ROUT TIN VCC VCC TO RIN TOUT VOUT = HI-Z POWERED DETECTOR DOWN UART WAKE-UP LOGIC EN = VCC ISL4221E, ISL4223E |
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