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ICL3225E Datasheet(PDF) 10 Page - Intersil Corporation |
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ICL3225E Datasheet(HTML) 10 Page - Intersil Corporation |
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10 / 20 page  10 FN4900.9 February 27, 2006 When using both manual and enhanced automatic powerdown (FORCEON = 0), the ICL32XXE won’t power up from manual powerdown until both FORCEOFF and FORCEON are driven high, or until a transition occurs on a receiver or transmitter input. Figure 5 illustrates a circuit for ensuring that the ICL32XXE powers up as soon as FORCEOFF switches high. The rising edge of the Master Powerdown signal forces the device to power up, and the ICL32XXE returns to enhanced automatic powerdown mode an RC time constant after this rising edge. The time constant isn’t critical, because the ICL32XXE remains powered up for 30 seconds after the FORCEON falling edge, even if there are no signal transitions. This gives slow-to-wake systems (e.g., a mouse) plenty of time to start transmitting, and as long as it starts transmitting within 30 seconds both systems remain enabled. INVALID Output The INVALID output always indicates (see Table 2) whether or not 30 µs have elapsed with invalid RS-232 signals (see Figures 6 and 8) persisting on all of the receiver inputs, giving the user an easy way to determine when the interface block should power down. Invalid receiver levels occur whenever the driving peripheral’s outputs are shut off (powered down) or when the RS-232 interface cable is disconnected. 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). Enhanced Automatic Powerdown Even greater power savings is available by using these devices which feature an enhanced automatic powerdown function. When the enhanced powerdown logic determines that no transitions have occurred on any of the transmitter nor receiver inputs for 30 seconds, the charge pump and transmitters powerdown, thereby reducing supply current to 1 µA. The ICL32XXE automatically powers back up whenever it detects a transition on one of these inputs. This automatic powerdown feature provides additional system power savings without changes to the existing operating system. Enhanced automatic powerdown operates when the FORCEON input is low, and the FORCEOFF input is high. Tying FORCEON high disables automatic powerdown, but manual powerdown is always available via the overriding FORCEOFF input. Table 2 summarizes the enhanced automatic powerdown functionality. Figure 7 illustrates the enhanced powerdown control logic. Note that once the ICL32XXE enters powerdown (manually or automatically), the 30 second timer remains timed out FIGURE 4. CONNECTIONS FOR MANUAL POWERDOWN WHEN NO VALID RECEIVER SIGNALS ARE PRESENT PWR FORCEOFF INVALID CPU I/O FORCEON ICL32XXE MGT LOGIC UART FIGURE 5. CIRCUIT TO ENSURE IMMEDIATE POWER UP WHEN EXITING FORCED POWERDOWN FORCEOFF FORCEON POWER MASTER POWERDOWN LINE 1M Ω 0.1 µF MANAGEMENT UNIT ICL32XXE FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS 0.3V -0.3V -2.7V 2.7V INVALID LEVEL - INVALID = 0 VALID RS-232 LEVEL - INVALID = 1 VALID RS-232 LEVEL - INVALID = 1 INDETERMINATE INDETERMINATE FIGURE 7. ENHANCED AUTOMATIC POWERDOWN LOGIC 30s TIMER S R FORCEOFF AUTOSHDN FORCEON R_IN T_IN EDGE DETECT EDGE DETECT ICL3225E, ICL3227E, ICL3245E |
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Similar Description - ICL3225E |
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