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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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ISL4244EIR Arkusz danych(PDF) 11 Page - Intersil Corporation |
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ISL4244EIR Arkusz danych(HTML) 11 Page - Intersil Corporation |
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11 / 17 page  11 FN8038.5 May 13, 2010 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). INVALID switches high 1µs after detecting a valid RS-232 level on a receiver input. INVALID operates in all modes (forced or automatic power-down, or forced on), so it is also useful for systems employing manual power-down circuitry.= Enhanced Automatic Power-down Even greater power savings is available by using these devices which feature an enhanced automatic power-down function. When the enhanced power-down logic determines that no transitions have occurred on any of the transmitter nor receiver inputs for 30 seconds, the charge pump and transmitters power-down, thereby reducing supply current to 10nA. The ISL4238E, ISL4244E, ISL4245 automatically powers back up whenever it detects a transition on one of these inputs. This automatic power-down feature provides additional system power savings without changes to the existing operating system. Enhanced automatic power-down operates when the FORCEON input is low, and the FORCEOFF input is high. Tying FORCEON high disables automatic power-down, but manual power-down is always available via the overriding FORCEOFF input. Table 2 summarizes the enhanced automatic power-down functionality. Figure 7 illustrates the enhanced power-down control logic. Note that once the ISL4238E, ISL4244E, ISL4245 enters power-down (manually or automatically), the 30 second timer remains timed out (set), keeping the ISL4238E, ISL4244E, ISL4245 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 30µs (see Figure 9), but this has no direct effect on the state of the ISL4238E, ISL4244E, ISL4245 (see the next sections for methods of utilizing INVALID to power down the device). The time to recover from automatic power-down mode is typically 100µs. Emulating Standard Automatic Power-down If enhanced automatic power-down isn’t desired, the user can implement the standard automatic power-down feature (mimics the function on the ISL4243E) by connecting the INVALID output to the FORCEON and FORCEOFF inputs, as shown in Figure 8. After 30µs of invalid receiver levels, INVALID switches low and drives the ISL4238E, ISL4244E, ISL4245 into a forced power-down condition. INVALID switches high as soon as a receiver input senses a valid RS-232 level, forcing the ISL4238E, ISL4244E, ISL4245 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 another computer via a detachable cable. Detaching the cable allows the internal receiver pull-down resistors to pull the inputs to GND (an invalid RS-232 level), causing the 30µs timer to time-out and drive the IC into power-down. Reconnecting the cablerestores valid levels, causing the IC to power back up. 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 POWER-DOWN LOGIC 30sec TIMER S R FORCEOFF AUTOPWDN FORCEON R_IN T_IN EDGE DETECT EDGE DETECT FIGURE 8. CONNECTIONS FOR AUTOMATIC POWER-DOWN WHEN NO VALID RECEIVER SIGNALS ARE PRESENT FORCEOFF INVALID CPU I/O FORCEON ISL4238E UART ISL4244E ISL4245 ISL4238E, ISL4244E, ISL4245E |
Podobny numer części - ISL4244EIR |
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Podobny opis - ISL4244EIR |
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