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LTC2873 Datasheet(PDF) 17 Page - Analog Devices |
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LTC2873 Datasheet(HTML) 17 Page - Analog Devices |
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17 / 32 page  LTC2873 17 REV B For more information www.analog.com Figure 16. Simplified DC/DC Converter with Required External Components The LTC2873 is a flexible multiprotocol transceiver sup- porting RS485/RS422 and RS232 protocols. Thisdevicecanbepoweredfromasingle3Vto5.5Vsupply with optional logic interface supply as low as 1.7V. An inte- grated DC/DC converter provides the positive and negative supply rails needed for RS232 operation. Automatically selected integrated termination resistors for both RS232 andRS485protocolsareincluded,eliminatingtheneedfor external termination components and switching relays. A logic loopback control is included for self-test and debug. The LTC2873 bus interface is a single two-pin port that can be configured as either an RS232 driver/receiver pair or a differential RS485 (and RS422) transceiver depending on the state of the 485/232 pin. In RS485 mode, the driver andreceivercanbeenabledindependentlywiththeDE485/ F232 and RE485 pins, or by tying these signals together, a single control selects transmit or receive modes. A 120Ω terminationresistorisautomaticallyengagedbetweenpins A/DO and B/RI in RS485 mode if TE485 is low. When the LTC2873 is in RS232 mode, the RS232 driver and receivers are both active and a 5k resistor is engaged at the receiver input to ground. The slew rate in RS232 mode can be set to support 1Mbps or 250kbps operation using the DE485/F232 pin. APPLICATIONS INFORMATION The LTC2873 features rugged operation with ESD ratings of ±26kV HBM on the RS232 and RS485 receiver inputs and driver outputs, both unpowered and powered. All other pins offer protection exceeding ±4kV. DC/DC Converter The on-chip DC/DC converter operates from the VCC input, generating a 7.0V VDD supply and a charge pumped –6.3V VEE supply, as shown in Figure 16. VDD and VEE power the output stage of the RS232 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 2.2µF. The charge pump capacitor (C1) is 220nF and the storage capacitors (C2 and C3) are 1µF. Locate C1 – C4 close to their associated pins shown in Figure 16. Refer to Layout Considerations section for guidance on circuit board layout. Bypass capacitor C5 on the logic supply pin can be omitted if VL is connected to VCC. See the VL Logic Supply section for more details about the VL logic supply. 2873 F16 BOOST REGULATOR VCC 3V TO 5.5V VL 1.7V TO VCC C1 220nF L1 10µH C4 2.2µF VCC VDD VEE SW GND GND CAP C5 0.1µF C2 1µF C3 1µF VL 14 12 9 22 20 13 10 11 NOTE: NOT ALL PINS SHOWN. IN THE CASE OF DUPLICATE PINS FOR VCC, GND, AND VEE, EXTERNAL COMPONENTS SHOULD BE POSITIONED CLOSEST TO THE NUMBERED PIN SHOWN ABOVE. |
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Similar Description - LTC2873 |
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