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ISL3232E Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL3232E Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 14 page 9 FN6045.3 February 13, 2008 Automatic Power-down (Excluding ISL3232E) Even greater power savings is available by using the automatic power-down function. When no valid RS-232 voltages (see Figure 6) are sensed on any receiver input for 30µs, the charge pump and transmitters power-down, thereby reducing supply current to 150nA. Invalid receiver levels occur whenever the driving peripheral’s outputs are shut off (powered down) or when the RS-232 interface cable is disconnected. The ISL4221E, ISL4223E powers back up whenever it detects a valid RS-232 voltage level on any receiver input. This automatic power-down feature provides additional system power savings without changes to the existing operating system. 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 automatic power-down functionality. Some applications may need more time to wake up from shutdown. If automatic power-down is being utilized, the RS-232 device will re-enter power-down if valid receiver levels aren’t reestablished within 30µs of the ISL4221E, ISL4223E powering up. Figure 5 illustrates a circuit that keeps the ISL4221E, ISL4223E from initiating automatic power-down for 100ms after powering up. This gives the slow-to-wake peripheral circuit time to re-establish valid RS-232 output levels. The time to recover from automatic power-down mode is typically 100µs. INVALID Output (Excluding ISL3232E) The INVALID output always indicates whether or not a valid RS-232 signal (see Figure 6) 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. 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). INVALID switches low after invalid levels have persisted on all of the receiver inputs for more than 30µs (see Figure 7). INVALID switches back 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. When automatic power-down is utilized, INVALID = 0 indicates that the ISL4221E, ISL4223E is in power-down mode. Capacitor Selection The charge pumps require 0.1µF, or greater, capacitors for proper operation. Increasing the capacitor values (by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. When using minimum required capacitor values, make sure that capacitor values do not degrade excessively with temperature. If in doubt, use capacitors with a larger nominal value. The capacitor’s equivalent series resistance (ESR) usually rises at low temperatures and it influences the amount of ripple on V+ and V- . FIGURE 6. DEFINITION OF VALID RS-232 RECEIVER LEVELS 0.3V -0.3V -2.7V 2.7V INVALID LEVEL - POWER-DOWN OCCURS AFTER 30µs VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE VALID RS-232 LEVEL - ISL4221E, ISL4223E IS ACTIVE INDETERMINATE - POWER-DOWN MAY OR INDETERMINATE - POWER-DOWN MAY OR MAY NOT OCCUR MAY NOT OCCUR RECEIVER INPUTS TRANSMITTER OUTPUTS INVALID OUTPUT V+ VCC 0 V- VCC 0 tINVL tINVH INVALID REGION } FIGURE 7. AUTOMATIC POWER-DOWN AND INVALID TIMING DIAGRAMS AUTOPWDN PWR UP ISL3232E, ISL4221E, ISL4223E |
Similar Part No. - ISL3232E |
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Similar Description - ISL3232E |
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