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ISL4238EIR Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL4238EIR Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 17 page 10 FN8038.5 May 13, 2010 Power-down Functionality The already low current requirement drops significantly when the device enters power-down mode. In power-down, supply current drops to 10nA, because the on-chip charge pump turns off (V+ collapses to VCC, V- collapses to GND), and the transmitter outputs tristate. Inverting receiver outputs disable only in manual power-down; refer to Table 2 for details. This micro-power mode makes these devices ideal for battery powered and portable applications. Software Controlled (Manual) Power-down These devices allow the user to force the IC into the low power, standby state, and 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 enhanced automatic power-down circuitry. ISL4238E, ISL4244E, ISL4245 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 enhanced 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. When using both manual and enhanced automatic power- down (FORCEON = 0), the ISL4238E, ISL4244E, ISL4245 won’t power up from manual power-down 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 ISL4238E, ISL4244E, ISL4245 powers up as soon as FORCEOFF switches high. The rising edge of the Master Power-down signal forces the device to power up, and the ISL4238E, ISL4244E, ISL4245 returns to enhanced automatic power- down mode an RC time constant after this rising edge. The time constant isn’t critical, because the ISL4238E, ISL4244E, ISL4245 remains powered up for 30s 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 30s both systems remain enabled. INVALID Output The INVALID output always indicates (see Table 2) whether or not 30µs have elapsed with invalid RS-232 signals (see Figures 6 and 9) 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 FIGURE 3. DISABLED RECEIVERS PREVENT POWER DRAIN ISL4238E TRANSITION RX TX ROUTB ROUT T1IN FORCEOFF = GND VCC VCC TO RIN T1OUT VOUT = HI-Z POWERED DETECTOR DOWN UART WAKE-UP LOGIC ISL4244E ISL4245 FIGURE 4. CONNECTIONS FOR MANUAL POWER-DOWN WHEN NO VALID RECEIVER SIGNALS ARE PRESENT PWR FORCEOFF INVALID CPU I/O FORCEON ISL4238E MGT LOGIC UART ISL4244E ISL4245 FIGURE 5. CIRCUIT TO ENSURE IMMEDIATE POWER UP WHEN EXITING FORCED POWER-DOWN FORCEOFF FORCEON POWER MASTER POWER-DOWN LINE 1M Ω 0.1µF MANAGEMENT UNIT ISL4238E, ISL4244E, ISL4245 ISL4238E, ISL4244E, ISL4245E |
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