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ICL3224 Datasheet(PDF) 8 Page - Intersil Corporation |
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ICL3224 Datasheet(HTML) 8 Page - Intersil Corporation |
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8 / 18 page  8 FN4876.10 March 1, 2006 Detailed Description These ICL32XX interface ICs operate from a single +3V to +5.5V supply, guarantee a 250kbps minimum data rate, require only four small external 0.1 µF capacitors, feature low power consumption, and meet all ElA RS-232C and V.28 specifications. The circuit is divided into three sections: The charge pump, the transmitters, and the receivers. Charge-Pump Intersil’s new ICL32XX family utilizes regulated on-chip dual charge pumps as voltage doublers, and voltage inverters to generate ±5.5V transmitter supplies from a V CC supply as low as 3.0V. This allows these devices to maintain RS-232 compliant output levels over the ±10% tolerance range of 3.3V powered systems. The efficient on-chip power supplies require only four small, external 0.1 µF capacitors for the voltage doubler and inverter functions at VCC = 3.3V. See the “Capacitor Selection” section, and Table 3 for capacitor recommendations for other operating conditions. The charge pumps operate discontinuously (i.e., they turn off as soon as the V+ 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. 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. All devices guarantee a 250kbps data rate for full load conditions (3k Ω and 1000pF), V CC ≥ 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 1Mbps. Transmitter inputs float if left unconnected, and may cause ICC increases. Connect unused inputs to GND for the best performance. Receivers All the ICL32XX devices contain standard inverting receivers, but only the ICL3238 and ICL3244 receivers can tristate, via the FORCEOFF control line. Additionally, the ICL3238 and ICL3244 include a noninverting (monitor) receiver (denoted by the ROUTB label) that is always active, regardless of the state of any control lines. Both receiver types 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. The ICL3238 and ICL3244 inverting receivers disable during forced (manual) powerdown, but not during automatic powerdown (see Table 2). Conversely, the monitor receiver remains active even during manual powerdown making it extremely useful for Ring Indicator monitoring. Standard receivers driving powered down peripherals must be disabled to prevent current flow through the peripheral’s protection diodes (see Figures 2 and 3). This renders them useless for wake up functions, but the corresponding monitor receiver can be dedicated to this task as shown in Figure 3. 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 ICL3238/44 TRANSITION RX TX R2OUTB R2OUT T1IN FORCEOFF = GND VCC VCC TO R2IN T1OUT VOUT = HI-Z POWERED DETECTOR DOWN UART WAKE-UP LOGIC ICL3224, ICL3226, ICL3238, ICL3244 |
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Similar Description - ICL3224 |
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