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ISL4241EIRZ Folha de dados(PDF) 9 Page - Intersil Corporation |
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ISL4241EIRZ Folha de dados(HTML) 9 Page - Intersil Corporation |
9 / 14 page 9 FN8037.7 June 10, 2010 Software Controlled (Manual) Power-down Most devices in the ISL4241E, ISL4243E family provide pins that allow the user to force the IC into the low power, standby state. On the ISL4241E, the power-down control is via a simple shutdown (SHDN) pin. Driving this pin high enables normal operation, while driving it low forces the IC into it’s power-down state. Connect SHDN to VCC if the power-down function isn’t needed. Note that all the receiver outputs remain enabled during shutdown (see Table 2). For the lowest power consumption during power-down, the receivers should also be disabled by driving the EN input high (see next section, and Figures 2 and 3). The ISL4243E utilize 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 ISL4243E inverting (standard) receiver outputs also disable when the device is in manual power-down, thereby eliminating the possible current path through a shutdown peripheral’s input protection diode (see Figures 2 and 3). Connecting FORCEOFF and FORCEON together disables the automatic power-down feature, enabling them to function as a manual SHUTDOWN input (see Figure 4). With any of the previous mentioned control schemes, the time required to exit power-down, and resume transmission is only 100µs. A mouse, or other application, may need more time to wake up from shutdown. If automatic power-down is being utilized, the RS-232 device will reenter power-down if valid receiver levels aren’t reestablished within 30µs of the ISL4243E powering up. Figure 5 illustrates a circuit that keeps the ISL4243E from initiating automatic power-down for 100ms after powering up. This gives the slow-to-wake peripheral circuit time to reestablish valid RS-232 output levels. INVALID Output (ISL4243E Only) 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 FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN ISL4241E TRANSITION RX TX R2OUTB R2OUT T1IN FORCEOFF = GND VCC VCC TO R2IN T1OUT VOUT = HI-Z POWERED DETECTOR DOWN UART WAKE-UP LOGIC OR SHDN = GND, EN = VCC ISL4243E FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN WHEN NO VALID RECEIVER SIGNALS ARE PRESENT PWR FORCEOFF INVALID CPU I/O FORCEON ISL4243E MGT LOGIC UART FIGURE 5. CIRCUIT TO PREVENT AUTO POWER-DOWN FOR 100ms AFTER FORCED POWERUP ISL4243E FORCEOFF FORCEON POWER MASTER POWER-DOWN LINE 1M Ω 0.1µF MANAGEMENT UNIT ISL4241E, ISL4243E |
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Descrição semelhante - ISL4241EIRZ |
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