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ISL4244EIR 데이터시트(PDF) 9 Page - Intersil Corporation |
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ISL4244EIR 데이터시트(HTML) 9 Page - Intersil Corporation |
9 / 17 page 9 FN8038.5 May 13, 2010 GND for the best performance. ISL4238E transmitter inputs incorporate an active positive feedback resistor that maintains the last input state in the absence of a forcing signal, so unused transmitter inputs may be left unconnected. Receivers ISL4238E, ISL4244E, ISL4245 devices contain standard inverting receivers which can tristate via the FORCEOFF control line. Additionally, they 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 3k Ω 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. The ISL4238E, ISL4244E, ISL4245 inverting receivers disable during forced (manual) power-down, but not during automatic power-down (see Table 2). Conversely, the monitor receiver remains active even during manual power- down 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. Low Power Operation These 3V devices require a nominal supply current of 0.3mA, even at VCC = 5.5V, during normal operation (not in power-down 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. TABLE 2. POWER-DOWN LOGIC TRUTH TABLE RCVR OR XMTR EDGE WITHIN 30 SEC? FORCEOFF INPUT FORCEON INPUT TRANSMITTER OUTPUTS RECEIVER OUTPUTS ROUTB OUTPUTS RS-232 LEVEL PRESENT AT RECEIVER INPUT? INVALID OUTPUT MODE OF OPERATION NO H H Active Active Active No L Normal Operation (Enhanced Auto Power-down Disabled) NO H H Active Active Active Yes H YES H L Active Active Active No L Normal Operation (Enhanced Auto Power-down Enabled) YES H L Active Active Active Yes H NO H L High-Z Active Active No L Power-down Due to Enhanced Auto Power-down Logic NO H L High-Z Active Active Yes H X L X High-Z High-Z Active No L Manual Power-down X L X High-Z High-Z Active Yes H INVALID DRIVING FORCEON AND FORCEOFF (EMULATES AUTOMATIC POWER-DOWN) X Note 8 Note 8 Active Active Active Yes H Normal Operation X Note 8 Note 8 High-Z High-Z Active No L Forced Auto Power-down NOTE: 8. Input is connected to INVALID Output. 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 ISL4238E, ISL4244E, ISL4245E |
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