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Zakładka z wyszukiwarką danych komponentów |
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Zakładka z wyszukiwarką danych komponentów |
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ISL4241EIRZ-T Arkusz danych(PDF) 10 Page - Intersil Corporation |
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ISL4241EIRZ-T Arkusz danych(HTML) 10 Page - Intersil Corporation |
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10 / 14 page  10 FN8037.7 June 10, 2010 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 ISL4243E is in power-down mode. Automatic Power-down (ISL4243E Only) Even greater power savings is available by using the ISL4243E which features an automatic power-down function. When no valid RS-232 voltages (see Figure 5) are sensed on any receiver input for 30µs, the charge pump and transmitters power-down, thereby reducing supply current to 10nA. 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 ISL4243E 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. The time to recover from automatic power-down mode is typically 100µs. 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- . Power Supply Decoupling In most circumstances a 0.1µF bypass capacitor is adequate. In applications that are particularly sensitive to power supply noise, decouple VCC to ground with a capacitor of the same value as the charge-pump capacitor C1. Connect the bypass capacitor as close as possible to the IC. Transmitter Outputs when Exiting Power-down Figure 8 shows the response of two transmitter outputs when exiting power-down mode. As they activate, the two transmitter outputs properly go to opposite RS-232 levels, with no glitching, ringing, nor undesirable transients. Each transmitter is loaded with 3k Ω in parallel with 2500pF. Note that the transmitters enable only when the magnitude of the supplies exceed approximately 3V. 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 - ISL4243E IS ACTIVE VALID RS-232 LEVEL - ISL4243E 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 ISL4241E, ISL4243E |
Podobny numer części - ISL4241EIRZ-T |
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Podobny opis - ISL4241EIRZ-T |
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