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ICL3221EM Datasheet(PDF) 7 Page - Intersil Corporation |
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ICL3221EM Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 12 page 7 FN7552.0 December 17, 2009 The ICL3221EM utilizes a two pin approach where the FORCEON and FORCEOFF inputs determine the IC’s mode. For always enabled operation, FORCEON and FORCEOFF are both strapped high. To switch between active and power-down modes, under logic or software control, only the FORCEOFF input need be driven. The FORCEON state isn’t critical, as FORCEOFF dominates over FORCEON. Nevertheless, if strictly manual control over power-down is desired, the user must strap FORCEON high to disable the automatic power-down circuitry. The INVALID output always indicates whether or not a valid RS-232 signal is present at any of the receiver inputs (see Table 2), giving the user an easy way to determine when the interface block should power down. In the case of a disconnected interface cable where all the receiver inputs are floating (but pulled to GND by the internal receiver pull down resistors), the INVALID logic detects the invalid levels and drives the output low. The power management logic then uses this indicator to power down the interface block. Reconnecting the cable restores valid levels at the receiver inputs, INVALID switches high, and the power management logic wakes up the interface block. INVALID can also be used to indicate the DTR or RING INDICATOR signal, as long as the other receiver inputs are floating, or driven to GND (as in the case of a powered down driver). Connecting FORCEOFF and FORCEON together disables the automatic power-down feature, enabling them to function as a manual SHUTDOWN input (see Figure 4). TABLE 2. POWER-DOWN AND ENABLE LOGIC TRUTH TABLE RS-232 SIGNAL PRESENT AT RECEIVER INPUT? FORCEOFF OR SHDN INPUT FORCEON INPUT EN INPUT TRANSMITTER OUTPUTS RECEIVER OUTPUTS INVALID OUTPUT MODE OF OPERATION ICL3221EM No H H L Active Active L Normal Operation (Auto Power-down Disabled) No H H H Active High-Z L Yes H L L Active Active H Normal Operation (Auto Power-down Enabled) Yes H L H Active High-Z H No H L L High-Z Active L Power-down Due to Auto Power-down Logic No H L H High-Z High-Z L Yes L X L High-Z Active H Manual Power-down Yes L X H High-Z High-Z H Manual Power-down with Receiver Disabled No L X L High-Z Active L Manual Power-down No L X H High-Z High-Z L Manual Power-down with Receiver Disabled 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 ICL324XE TRANSITION RX TX R2OUTB R2OUT T1IN FORCEOFF = GND VCC VCC TO R2IN T1OUT VOUT = HI-Z POWERED OR SHDN = GND, EN = VCC DETECTOR DOWN UART WAKE-UP LOGIC ISL3221EM |
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