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ICL3226E Datasheet(PDF) 11 Page - Intersil Corporation |
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ICL3226E Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 20 page  11 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 (set), keeping the ICL32XXE powered down until FORCEON transitions high, or until a transition occurs on a receiver or transmitter input. The INVALID output signal switches low to indicate that invalid levels have persisted on all of the receiver inputs for more than 30 µs (see Figure 8), but this has no direct effect on the state of the ICL32XXE (see the next sections for methods of utilizing INVALID to power down the device). INVALID switches high 1 µs after detecting a valid RS-232 level on a receiver input. INVALID operates in all modes (forced or automatic powerdown, or forced on), so it is also useful for systems employing manual powerdown circuitry. The time to recover from automatic powerdown mode is typically 100 µs. Emulating Standard Automatic Powerdown If enhanced automatic powerdown isn’t desired, the user can implement the standard automatic powerdown feature (mimics the function on the ICL3221E/23E/43E) by connecting the INVALID output to the FORCEON and FORCEOFF inputs, as shown in Figure 9. After 30 µs of invalid receiver levels, INVALID switches low and drives the ICL32XXE into a forced powerdown condition. INVALID switches high as soon as a receiver input senses a valid RS-232 level, forcing the ICL32XXE to power on. See the “INVALID DRIVING FORCEON AND FORCEOFF” section of Table 2 for an operational summary. This operational mode is perfect for handheld devices that communicate with 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 ICL3224E, ICL3226E, ICL3244E |
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Similar Description - ICL3226E |
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