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ICL3217EIAZ Datasheet(PDF) 6 Page - Intersil Corporation |
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ICL3217EIAZ Datasheet(HTML) 6 Page - Intersil Corporation |
6 / 12 page 6 Receivers The ICL32X7E each contain inverting receivers that convert RS-232 signals to CMOS output levels and accept inputs up to ±25V while presenting the required 3kΩ to 7kΩ 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 on the ICL3207E are always active. The ICL3217E receivers disable when in the automatic powerdown state, thereby eliminating the possible current path through a shutdown peripheral’s input protection diode (see Figures 2 and 3). 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 11mA current required by comparable 5V RS-232 devices, allowing users to reduce system power simply by replacing the old style device with the ICL3207E. Low Power, Pin Compatible Replacement Pin compatibility with existing 5V products (e.g., MAX207E), coupled with the wide operating supply range, make the ICL32X7E potential lower power, higher performance drop- in replacements for existing ‘2X7E 5V applications. As long as the ±5V RS-232 output swings are acceptable, the ICL32X7E devices should work in most 5V applications. When replacing a ‘207E or ‘237E device in an existing 5V application, it is acceptable to terminate C3 to VCC as shown on the Typical Operating Circuit. Nevertheless, terminate C3 to GND if possible, as slightly better performance results from this configuration. Automatic Powerdown (ICL3217E Only) Even greater power savings is available by using the ICL3217E which features an automatic powerdown function. When no valid RS-232 voltages (see Figure 4) are sensed on any receiver input for 30 µs, the ICL3217E automatically enters its powerdown state (see Figure 5). In powerdown, supply current drops to 1 µA, because the on-chip charge pump turns off (V+ collapses to VCC, V- collapses to GND), and the receiver and transmitter outputs three-state (see Table 2). This micro-power mode makes the ICL3217E ideal for battery powered and portable applications. Invalid receiver levels occur whenever the driving peripheral’s outputs are shut off (powered down) or when the RS-232 interface cable is disconnected. The ICL3217E powers back up whenever it detects a valid RS-232 voltage level on any receiver input (such as when the RS-232 cable is reconnected). The time to recover from automatic powerdown mode is typically 100 µs. 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 VCC Rx Tx VCC CURRENT FLOW VOUT = VCC RS-232 CHIP DOWN UART SHDN = GND TABLE 2. ICL3217E AUTOMATIC POWERDOWN OPERATION RS-232 SIGNAL PRESENT AT RECEIVER INPUT? TRANSMITTER OUTPUTS RECEIVER OUTPUTS MODE OF OPERATION YES Active Active Normal Operation NO High-Z High-Z Powerdown Due to Auto Powerdown Logic FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN ICL3217E TRANSITION DETECTOR RX TX VCC VCC TO VOUT = HI-Z* WAKE-UP LOGIC POWERED DOWN UART V- * IN AUTOMATIC POWERDOWN ICL3207E, ICL3217E |
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