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LTC2801 Datasheet(PDF) 10 Page - Linear Technology |
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LTC2801 Datasheet(HTML) 10 Page - Linear Technology |
10 / 18 page LTC2801/LTC2802/ LTC2803/LTC2804 0 2801234fe BOOST REGULATOR VEE VDD C3 1µF C2 1µF CAP SW C1 220nF L1 10µH VCC C4 1µF C5 220nF *OMIT IF VL IS CONNECTED TO VCC * VL 1.8V TO 5.5V 1.8V TO 5.5V 2801 F06 aPPlicationS inForMation Overview The LTC2801 family of RS-232 transceivers operates on a VCC supply of 1.8V to 5.5V, utilizing a switching regula- tor to generate the necessary higher voltage rails for the drivers. The transceivers interface with logic operating on any supply from 1.8V to 5.5V, independent of the VCC voltage. Depending on the device, one or two control pins are available to invoke Shutdown, Receiver Active and Driver Disable features. DC-DC Converter The on-chip DC-DC converter operates from the VCC input, generating a 7V VDD supply and a charge pumped –6.3V VEE supply, as shown in Figure 6. VDD and VEE power the output stage of the drivers and are regulated to levels that guarantee greater than ±5V output swing. The DC-DC converter requires a 10µH inductor (L1) and a bypass capacitor (C4) of at least 1µF. The recommended size for the charge pump capacitor (C1) is 220nF and for the storage capacitors (C2 and C3) is 1µF. Larger storage capacitors up to 4.7µF may be used if C1 is kept at 20% to 50% their size and C4 is also scaled. Locate C1-C4 close to their associated pins. Power-Saving Modes When the DC-DC converter and drivers are turned off (PS and MODE or ON/OFF = logic low), VCC supply current is reduced to 1µA. Tables 1 and 2 summarize the modes for each device. In Shutdown mode, VL supply current is reduced to 1µA, and both receiver and driver outputs assume a high im- pedance state. In Receivers Active mode, the quiescent VL supply current is reduced to 15µA and the driver outputs assume a high impedance state. The receivers operate at a reduced rate (typically 100 kbps) with hysteresis turned off. Half-Duplex Operation When the DC-DC converter is kept on (PS = logic high), MODEservesasalow-latencydriverenableforhalf-duplex operation. Each driver is enabled and disabled in less than 2µs, while each receiver remains continuously active. This mode of operation is illustrated in Figures 15-17. Battery Operation To maximize battery life, connect VCC (and L1) directly to the unregulated battery voltage and VL to the regulated supply, as shown in Figure 22. This configuration typically minimizes conversion loss while providing compatibility with system logic levels. Inductor Selection A 10µH inductor with a saturation current (ISAT) rating of at least 200mA and low DCR (copper wire resistance) is recommended. Some small inductors meeting these requirements are listed in Table 3. Figure 6. DC/DC Converter and Recommended Bypassing VL Logic Supply AseparatelogicsupplypinVLallowstheLTC2801familyto interface with any logic signal from 1.8V to 5.5V, as shown in Figure 7. Simply connect the desired logic supply to VL. There is no interdependency between VCC and VL; they may simultaneously operate at any voltage from 1.8V to 5.5Vandsequenceinanyorder.IfVLispoweredseparately from VCC, bypass VL with a 220nF capacitor (C5). Figure 7. VCC and VL Are Independent ANY VOLTAGE FROM 1.8V TO 5.5V ANY VOLTAGE FROM 1.8V TO 5.5V VL VCC EXTERNAL DEVICE RS-232 2801 F07 |
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Similar Description - LTC2801 |
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