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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination

LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination
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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 1

LTC2870/LTC2871 1 28701f TYPICAL APPLICATIONS DESCRIPTION RS232/RS485 Multiprotocol Transceivers with Integrated Termination The LTC®2870/LTC2871 are robust pin-configurable multiprotocol transceivers, supporting RS232, RS485, and RS422 protocols, operating on a single 3V to 5.5V supply. The LTC2870 can be configured as two RS232 single-ended transceivers or one RS485 differential transceiver on shared I/O lines. The LTC2871 offers independent control of two RS232 transceivers and one RS485 transceiver, each on dedicated I/O lines. Pin-controlled integrated termination resistors allow for easy interface reconfiguration, eliminating external resistors and control relays. Half-duplex switches allow four-wire and two-wire RS485 configurations. Loopback mode steers the driver inputs to the receiver outputs for diagnostic self-test.The RS485 receivers support up to 256 nodes per bus, and feature full failsafe operation for floating, shorted or terminated inputs. An integrated DC/DC boost converter uses a small inductor and one capacitor, eliminating the need for multiple supplies for driving RS232 levels. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protocol Switching with Automatic Termination Selection FEATURES APPLICATIONS n One RS485 and Two RS232 Transceivers n 3V to 5.5V Supply Voltage n 20Mbps RS485 and 500kbps RS232 n Automatic Selection of Integrated RS485 (120Ù) and RS232 (5kÙ)Termination Resistors n Half-/Full-Duplex RS485 Switching n High ESD: ±26kV (LTC2870), ±16kV (LTC2871) n Logic Loopback Mode n 1.7V to 5.5V Logic Interface n Supports Up to 256 RS485 Nodes n RS485 Receiver Failsafe Eliminates UART Lockup n Available in 28-Pin 4mm × 5mm QFN and TSSOP (LTC2870), and 38-Pin 5mm × 7mm QFN and TSSOP (LTC2871) n Flexible RS232/RS485/RS422 Interface n Software Selectable Multiprotocol Interface Ports n Point-of-Sale Terminals n Cable Repeaters n Protocol Translators Simultaneous Protocols and RS485 Termination Switching RS485 Duplex Switching 28701 TA01 LTC2870 1.7V TO VCC 3V TO 5.5V 1.7V TO VCC 3V TO 5.5V 1.7V TO VCC 3V TO 5.5V RS485 TERMINATION RS485 DUPLEX 485/232 DY Y Z A B DZ RA RB Y Z A B DI VL TE485 RO DIN1 ROUT2 DIN2 ROUT1 VL VCC VCC DOUT1 RIN2 DOUT2 RIN1 LTC2871 120Ù 120Ù Y VCC Z A B DI, DY RO, RB H/F LTC2870, LTC2871 FULL HALF RS232 RS485 OFF ON VL

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 3

LTC2870/LTC2871 3 28701f ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2870CFE#PBF LTC2870IFE#PBF LTC2870CFE#TRPBF LTC2870IFE#TRPBF LTC2870FE LTC2870FE 28-Lead Plastic TSSOP 28-Lead Plastic TSSOP 0°C to 70°C –40°C to 85°C LTC2870CUFD#PBF LTC2870IUFD#PBF LTC2870CUFD#TRPBF LTC2870IUFD#TRPBF 2870 2870 28-Lead (4mm × 5mm) Plastic QFN 28-Lead (4mm × 5mm) Plastic QFN 0°C to 70°C –40°C to 85°C LTC2871CFE#PBF LTC2871IFE#PBF LTC2871CFE#TRPBF LTC2871IFE#TRPBF LTC2871FE LTC2871FE 38-Lead Plastic TSSOP 38-Lead Plastic TSSOP 0°C to 70°C –40°C to...

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 4

LTC2870/LTC2871 4 28701f ELECTRICAL CHARACTERISTICSThe l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supply VCC Supply Voltage Operating Range 3 5.5 V VL Logic Supply Voltage Operating Range VL VCC 1.7 VCC V VCC Supply Current in Shutdown Mode RXEN = VL, DXEN = TE485 = FEN = 0V, (LTC2870) DX485 = DX232 = TE485 = FEN = H/F = 0V, RX485 = RX232 = VL (LTC2871) l 8 60 ìA VCC Supply Current in Transceiver...

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 5

LTC2870/LTC2871 5 28701f E LECTRICAL CHARACTERISTICSThe l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RTERM Terminating Resistor TE485 = VL, A – B = 2V, B = –7V, 0V, 10V (Figure 8) (Note 5) l 108 120 156 Ù RS232 Driver VOLD Output Low Voltage RL = 3kÙ; VEE –5.9V l –5 –5.7 –7.5 V VOHD Output High Voltage RL = 3kÙ; VDD 6.5V l 5 6.2 7.5 V Three-State (High Impedance) Output Current Y or Z (LTC2870) = ±15V...

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 6

LTC2870/LTC2871 6 28701f ELECTRICAL CHARACTERISTICSThe l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. VL VCC. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 AC Characteristics Maximum Data Rate (Note 3) l 20 Mbps tPLHD485 tPHLD485 Driver Propagation Delay RDIFF = 54Ù, CL = 100pF (Figure 4) l 20 70 ns Driver Propagation Delay Difference |tPLHD485 – tPHLD485| RDIFF = 54Ù, CL = 100pF (Figure 4) l 1 6 ns tSKEWD485 Driver Skew (Y to Z) RDIFF = 54Ù, CL...

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 7

LTC2870/LTC2871 7 28701f TYPICAL PERFORMANCE CHARACTERISTICS VCC Supply Current vs RS232 Data Rate VCC Supply Current vs Supply Voltage, All Transceivers at Max Rate (LTC2871) RS485 Driver Differential Output Voltage vs Temperature RS485 Driver Propagation Delay vs Temperature RS485 Driver Skew vs Temperature RS485 Driver Short-Circuit Current vs Short-Circuit Voltage VCC Supply Current vs Supply Voltage in Shutdown Mode VCC Supply Current vs Supply Voltage in Fast Enable Mode VCC Supply Current vs RS485 Data Rate INPUT VOLTAGE (V) 3 INPUT CURRENET (ìA) 30 25 20 15 10 5 0 3.5 4.5 5 28701...

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LTC2870/LTC2871 - RS232/RS485 Multiprotocol Transceivers with Integrated Termination - 9

LTC2870/LTC2871 9 28701f PIN FUNCTIONS PIN NAME LTC2870 QFN LTC2870 TSSOP LTC2871 QFN LTC2871 TSSOP DESCRIPTION VCC 16, 20, 24 19, 23, 27 21, 27, 33 25, 31, 37 Input Supply (3V to 5.5V). Tie all three pins together and connect a 2.2ìF or larger capacitor between VCC (adjacent to VDD) and GND. VL 25 28 35 1 Logic Supply (1.7V to 5.5V) for the receiver outputs, driver inputs, and control inputs. Bypass this pin to GND with a 0.1ìF capacitor if not tied tot VCC. Keep VL VCC for proper operation. However, VL > VCC will not damage the device, provided that absolute maximum limits are respected....

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