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ltc2870/ltc2871 1 28701f typical applications description rs232/rs485 multiprotocol transceivers with integrated termination the ltc ? 2870/ltc2871 are robust pin-configurable mul- tiprotocol 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 induc- tor 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 (120) and rs232 (5k)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 v cc 3v to 5.5v 1.7v to v cc 3v to 5.5v 1.7v to v cc 3v to 5.5v rs485 termination rs485 duplex 485/ 232 dy y z a b dz ra rb y z a b di v l te485 ro din1 rout2 din2 rout1 v cc v l v cc dout1 rin2 dout2 rin1 ltc2871 120 120 y v cc z a b di, dy ro, rb h/ f ltc2870, ltc2871 half full rs485 rs232 on off v l
ltc2870/ltc2871 2 28701f ltc2870 ltc2870 9 10 top view 29 v ee ufd package 28-lead (4mm s 5mm) plastic qfn 11 12 13 28 27 26 25 24 14 23 6 5 4 3 2 1 v ee ra rb 485/ 232 rxen dxen dy dz a b v cc y gnd z v cc v dd te485 h/ f lb v l v cc gnd fen gnd cap v ee gnd sw 7 17 18 19 20 21 22 16 8 15 t jmax = 125c, ja = 43c/w exposed pad (pin 29) is v ee , must be soldered to pcb 1 2 3 4 5 6 7 8 9 10 11 12 13 14 top view fe package 28-lead plastic tssop 28 27 26 25 24 23 22 21 20 19 18 17 16 15 lb h/ f te485 v ee ra rb 485/ 232 rxen dxen dy dz fen gnd cap v l v cc gnd a b v cc y gnd z v cc v dd sw gnd v ee 29 v ee t jmax = 125c, ja = 25c/w exposed pad (pin 29) is v ee , must be soldered to pcb absolute maximum ratings input supplies v cc , v l ..................................................... C0.3v to 7v generated supplies v dd ................................................ v cc C 0.3v to 7.5v v ee ......................................................... 0.3v to C7.5v v dd C v ee ..............................................................15v sw ........................................... C0.3v to (v dd + 0.3v) cap ............................................. 0.3v to (v ee C 0.3v) a, b, y, z, rin1, rin2, dout1, dout2 ........C15v to 15v di, dz, dy, rxen , dxen, lb, h/ f , te485, rx485 , dx485, rx232 , dx232, din1, din2, 485/ 232 , ch2 . .......................................... C0.3v to 7v (notes 1 and 2) pin configuration fen, ra, rb, ro, rout1, rout2 ...C0.3v to (v l + 0.3v) differential enabled terminator voltage (a-b or y-z) ..........................................................6v operating temperature ltc2870c/ltc2871c ............................... 0c to 70c ltc2870i/ltc2871i ............................. C40c to 85c storage temperature range .................. C65c to 125c lead temperature (soldering, 10 sec) fe package........................................................ 300c
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 0c to 70c C40c to 85c ltc2870cufd#pbf ltc2870iufd#pbf ltc2870cufd#trpbf ltc2870iufd#trpbf 2870 2870 28-lead (4mm 5mm) plastic qfn 28-lead (4mm 5mm) plastic qfn 0c to 70c C40c to 85c ltc2871cfe#pbf ltc2871ife#pbf ltc2871cfe#trpbf ltc2871ife#trpbf ltc2871fe ltc2871fe 38-lead plastic tssop 38-lead plastic tssop 0c to 70c C40c to 85c ltc2871cuhf#pbf ltc2871iuhf#pbf ltc2871cuhf#trpbf ltc2871iuhf#trpbf 2871 2871 38-lead (5mm 7mm) plastic qfn 38-lead (5mm 7mm) plastic qfn 0c to 70c C40c to 85c consult ltc marketing for parts specified with wider operating temperature ranges. consult ltc marketing for information on non-standard lead based finish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ltc2871 ltc2871 13 14 15 16 top view 39 v ee uhf package 38-lead (5mm s 7mm) plastic qfn 17 18 19 38 37 36 35 34 33 32 24 25 26 27 28 29 30 31 8 7 6 5 4 3 2 1 v ee rout1 rout2 ch2 rx485 dx485 di din1 din2 dx232 rx232 v ee rin1 rin2 a b v cc y gnd z dout1 dout2 v cc v dd te485 h/ f lb v l ro v cc gnd fen gnd cap v ee gnd sw v ee 23 22 21 20 9 10 11 12 t jmax = 125c, ja = 34c/w exposed pad (pin 39) is v ee , must be soldered to pcb 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 top view fe package 38-lead plastic ssop 38 27 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 v l lb h/ f te485 v ee rout1 rout2 ch2 rx485 dx485 di din1 din2 dx232 rx232 v ee fen gnd cap ro v cc gnd rin1 rin2 a b v cc y gnd z dout1 dout2 v cc v dd v ee sw gnd v ee 39 v ee t jmax = 125c, ja = 29c/w exposed pad (pin 39) is v ee , must be soldered to pcb pin configurations part number configurable transceiver combinations (rs485 + rs232) packages ltc2870 (0 + 0), (1 + 0), (0 + 2) 28-lead qfn, 28-lead tssop ltc2871 (0 + 0), (1 + 0), (1 + 1), (1 + 2), (0 + 1), (0 + 2) 38-lead qfn, 38-lead tssop product selection guide
ltc2870/ltc2871 4 28701f electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v cc = v l = 3.3v, te485 = 0v, lb = 0v unless otherwise noted. symbol parameter conditions min typ max units power supply v cc supply voltage operating range 3 5.5 v v l logic supply voltage operating range v l v cc 1.7 v cc v v cc supply current in shutdown mode rxen = v l , dxen = te485 = fen = 0v, (ltc2870) dx485 = dx232 = te485 = fen = h/ f = 0v, rx485 = rx232 = v l (ltc2871) l 860 a v cc supply current in transceiver mode (outputs unloaded) (note 3) 485/ 232 = dxen = v l , rxen = 0v, dy/dz = 0v or v l (ltc2870) dx485 = dx232 = v l , rx485 = rx232 = 0v, di/din1/din2 = 0v or v l (ltc2871) 3.3 ma v l supply current in transceiver mode (outputs unloaded) l 05 a rs485 driver |v od | differential output voltage r l = , v cc = 3v (figure 1) r l = 27, v cc = 3v (figure 1) r l = 50, v cc = 3.13v (figure 1) l l l 1.5 1.5 2 6 v cc v cc v v v |v od | difference in magnitude of differential output voltage for complementary output states r l = 27, v cc = 3v (figure 1) r l = 50, v cc = 3.13v (figure 1) l l 0.2 0.2 v v v oc common mode output voltage r l = 27 or 50 (figure 1) l 3v |v oc | difference in magnitude of common mode output voltage for complementary output states r l = 27 or 50 (figure 1) l 0.2 v i ozd485 three-state (high impedance) output current v out = 12v or C7v, v cc = 0v or 3.3v (figure 2) l C100 125 a i osd485 maximum short-circuit current C7v v out 12v (figure 2) l C250 250 ma rs485 receiver i in485 input current v in = 12v or C7v, v cc = 0v or 3.3v (figure 3) (note 5) l C100 125 a r in485 input resistance v in = 12v or C7v, v cc = 0v or 3.3v (figure 3) (note 5) l 96 125 k differential input signal threshold voltage (a-b) C7v (a or b) 12v (note 5) l 200 mv input hysteresis b = 0v (notes 3, 5) 130 mv differential input failsafe threshold voltage C7v (a or b) 12v (note 5) l C200 C50 0 mv input dc failsafe hysteresis b = 0v (note 5) 25 mv v ol output low voltage output low, i(ra, ro) = 3ma (sinking), 3v v l 5.5v l 0.4 v output low, i(ra, ro) = 1ma (sinking), 1.7v v l < 3v l 0.4 v v oh output high voltage output high, i(ra, ro) = C3ma (sourcing), 3v v l 5.5v l v l C 0.4 v output high, i(ra, ro) = C1ma (sourcing), 1.7v v l < 3v l v l C 0.4 v three-state (high impedance) output current 0v (ra, ro), v l , v l = 5.5v l 05 a short-circuit output current 0v (ra, ro), v l , v l = 5.5v l 125 ma
ltc2870/ltc2871 5 28701f electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v cc = v l = 3.3v, te485 = 0v, lb = 0v unless otherwise noted. symbol parameter conditions min typ max units r term terminating resistor te485 = v l , a C b = 2v, b = C7v, 0v, 10v (figure 8) (note 5) l 108 120 156 rs232 driver v old output low voltage r l = 3k; v ee C5.9v l C5 C5.7 C7.5 v v ohd output high voltage r l = 3k; v dd 6.5v l 5 6.2 7.5 v three-state (high impedance) output current y or z (ltc2870) = 15v rs232 receiver enabled dout1 or dout2 (ltc2871) = 15v l l 156 10 a a output short-circuit current driver output = 0v l 35 90 ma rs232 receiver input threshold voltage l 0.6 1.5 2.5 v input hysteresis l 0.1 0.4 1.0 v output low voltage i(ra, rb, rout1, rout2) = 1ma (sinking) 1.7v v l 5.5v l 0.4 v output high voltage i(ra, rb, rout1, rout2) = C1ma (sourcing) 1.7v v l 5.5v l v l C 0.4 v input resistance C15v (a, b, rin1, rin2) 15v, rs232 receiver enabled l 357 k three-state (high impedance) output current 0v (ra, rb, rout1, rout2) v l l 05 a output short-circuit current v l = 5.5v 0v (ra, rb, rout1, rout2) v l l 25 50 ma logic inputs threshold voltage l 0.4 0.75 ? v l v input current l 05 a power supply generator v dd regulated v dd output voltage rs232 drivers enabled, outputs loaded with r l = 3k to gnd, din1/dy = v l , din2/dz = 0v (note 3) 7v v ee regulated v ee output voltage C6.3 v esd ltc2870 interface pins (a, b, y, z) human body model to gnd or v cc , powered or unpowered (note 7) 26 kv ltc2871 interface pins (a, b, y, z, rin1, rin2, dout1, dout2) 16 kv all other pins human body model (note 7) 4 kv
ltc2870/ltc2871 6 28701f electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25c. v cc = v l = 3.3v, te485 = 0v, lb = 0v unless otherwise noted. v l v cc . symbol parameter conditions min typ max units rs485 ac characteristics maximum data rate (note 3) l 20 mbps t plhd485 t phld485 driver propagation delay r diff = 54, c l = 100pf (figure 4) l 20 70 ns driver propagation delay difference |t plhd485 C t phld485 | r diff = 54, c l = 100pf (figure 4) l 16 ns t skewd485 driver skew (y to z) r diff = 54, c l = 100pf (figure 4) l 16 ns t rd485 , t fd485 driver rise or fall time r diff = 54, c l = 100pf (figure 4) l 15 ns t zld485 , t zhd485 , t lzd485 , t hzd485 driver output enable or disable time fen = v l , r l = 500, c l = 50pf (figure 5) l 120 ns t zhsd485 , t zlsd485 driver enable from shutdown r l = 500, c l = 50pf (figure 5) l 8s t plhr485 , t phlr485 receiver input to output c l = 15pf, v cm = 1.5v, |a C b| = 1.5v (figure 6) (note 5) l 65 85 ns t skewr485 differential receiver skew |t plhr485 C t phlr485 | c l = 15pf (figure 6) l 16 ns t rr485 , t fr485 receiver output rise or fall time c l = 15pf (figure 6) l 315 ns t zlr485 , t zhr485 , t lzr485 , t hzr485 receiver output enable or disable time fen = v l , r l = 1k, c l = 15pf (figure 7) l 50 ns t rten485 , t rtz485 termination enable or disable time fen = v l , v b = 0v, v ab = 2v (figure 8) (note 5) l 100 s rs232 ac characteristics maximum data rate r l = 3k, c l = 2500pf r l = 3k, c l = 500pf (note 3) l l 100 500 kbps kbps driver slew rate (figure 9) r l = 3k, c l = 2500pf r l = 3k, c l = 50pf l l 4 30 v/s v/s t phld232 , t plhd232 driver propagation delay r l = 3k, c l = 50pf (figure 9) l 12 s t skewd232 driver skew r l = 3k, c l = 50pf (figure 9) 50 ns t zld232 , t zhd232 , t lzd232 , t hzd232 driver output enable or disable time fen = v l , r l = 3k, c l = 50pf (figure 10) l 0.4 2 s t phlr232 , t plhr232 receiver propagation delay c l = 150pf (figure 11) l 60 200 ns t skewr232 receiver skew c l = 150pf (figure 11) 25 ns t rr232 , t fr232 receiver rise or fall time c l = 150pf (figure 11) l 60 200 ns t zlr232 , t zhr232 , t lzr232 , t hzr232 receiver output enable or disable time fen = v l , r l = 1k, c l = 150pf (figure 12) l 0.7 2 s power supply generator v dd /v ee supply rise time fen = , (notes 3 and 4) l 0.2 2 ms note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: all currents into device pins are positive; all currents out of device pins are negative. all voltages are referenced to device ground unless otherwise specified. note 3: guaranteed by other measured parameters and not tested directly. note 4: time from fen until v dd 5v and v ee C5v. external components as shown in the typical application section. note 5: condition applies to a, b for h/ f = 0v, and y, z for h/ f = v l . note 6: this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. overtemperature protection activates at a junction temperature exceeding 150c. continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. note 7: guaranteed by design and not subject to production test.
ltc2870/ltc2871 7 28701f typical performance characteristics v cc supply current vs rs232 data rate v cc 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 v cc supply current vs supply voltage in shutdown mode v cc supply current vs supply voltage in fast enable mode v cc supply current vs rs485 data rate input voltage (v) 3 input currenet (a) 30 25 20 15 10 5 0 4.5 5 3.5 28701 g01 5.5 4 h/ f low h/ f high supply voltage (v) 3 supply current (ma) 5 4 3 2 1 4.5 5 3.5 28701 g02 5.5 4 C40c 25c 85c all drivers and receivers disabled te485 low data rate (mbps) 0.1 supply current (ma) 100 80 60 40 20 0 10 28701 g03 100 1 te high te low v cc = 5v v cc = 3.3v all rs485 drivers and receivers switching. cl = 100pf on each driver output. data rate (kbps) 0 input current (ma) 35 30 25 15 20 10 5 400 28701 g04 500 300 200 100 0.05nf 0.05nf 0.5nf 0.5nf 2.5nf 2.5nf v cc = 5v v cc = 3.3v all rs232 drivers and receivers switching. supply voltage (v) 3 supply current (ma) 120 110 100 90 80 70 4.5 5 3.5 28701 g05 5.5 4 85c all drivers and receivers switching. driver outputs tied to receiver inputs. rs232: 0.5mbps (cl = 500pf) rs485: 20mbps (cl = 100pf) te485 high 25c C40c temperature (c) C50 voltage (v) 4.5 3.5 2.5 1.5 4.0 3.0 2.0 1.0 0.5 0 50 75 C25 28701 g06 100 25 0 r l = 100 r l = 54 r l = 100 r l = 54 v cc = 5v v cc = 3.3v temperature (c) C50 delay (ns) 50 40 30 20 10 0 50 75 C25 28701 g06 100 25 0 v cc = 3.3v, v l = 1.7v v cc = 5v, v l = 1.7v v cc = 3.3v, v l = 3.3v v cc = 5v, v l = 5v temperature (c) C50 skew (ns) 3.0 2.5 1.5 2.0 1.0 0.5 0 50 75 C25 28701 g08 100 25 0 short-circuit voltage (v) C10 short-circuit current (ma) 150 100 0 50 C50 C100 C150 10 C5 28701 g09 15 5 0 output low output high v cc = 5v v cc = 3.3v t a = 25c, v cc = v l = 3.3v, unless otherwise noted.
ltc2870/ltc2871 8 28701f typical performance characteristics rs232 receiver input threshold vs temperature rs232 receiver output voltage vs load current rs485 termination resistance vs temperature rs232 operation at 500kbps rs485 operation at 20mbps ltc2870 drivers changing modes rs485 receiver propagation delay vs temperature rs485 receiver skew vs temperature rs485 receiver output voltage vs load current temperature (c) C50 delay (ns) 80 70 60 50 40 50 75 C25 28701 g10 100 25 0 v cc = 3.3v, v l = 1.7v v cc = 5v, v l = 1.7v v cc = 3.3v, v l = 3.3v v cc = 5v, v l = 5v temperature (c) C50 skew (ns) 3.0 2.5 2.0 1.0 1.5 0.5 0 50 75 C25 28701 g11 100 25 0 output current (ma) 0 output voltage (v) 6 5 4 2 3 1 0 8 2 28701 g12 10 6 4 v l = 5v v l = 3.3v v l = 1.7v temperature (c) C50 threshold voltage (v) 2.0 1.8 1.6 1.4 1.2 1.0 50 75 C25 28701 g13 100 25 0 v cc = 5v v cc = 3.3v input high input low output current (ma) 0 output voltage (v) 6 5 4 2 3 1 0 8 2 28701 g14 10 6 4 v l = 5v v l = 3.3v v l = 1.7v temperature (c) C50 resistance () 130 118 116 114 112 110 128 126 124 122 120 50 75 C25 28701 g15 100 25 0 v cm = C7v v cm = 2v v cm = 12v wrapping data dout loads: 5k + 50pf 5v/div 28701 g16 1s/div dout1 dout2 rout1 rout2 din1 din2 h/ f high y, z loads: 120 (diff) + 50pf 1v/div 5v/div 28701 g17 20ns/div ro y di z 5v/div 5v/div 28701 g18 2s/div rs232 mode rs485 mode rs232 mode y 485/ 232 z t a = 25c, v cc = v l = 3.3v, unless otherwise noted.
ltc2870/ltc2871 9 28701f pin functions pin name ltc2870 qfn ltc2870 tssop ltc2871 qfn ltc2871 tssop description v cc 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 2.2f or larger capacitor between v cc (adjacent to v dd ) and gnd. v l 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 0.1f capacitor if not tied tot v cc . keep v l v cc for proper operation. however, v l > v cc will not damage the device, provided that absolute maximum limits are respected. v dd 15 18 20 24 generated positive supply voltage for rs232 driver (+7v). connect 1f capacitor between v dd and gnd. v ee 1, 12, 29 4, 15, 29 1, 12, 16, 19, 39 5, 16, 20, 23, 39 generated negative supply voltage for rs232 driver (C 6.3v). tie all pins together and connect 1f capacitor between v ee (adjacent to the cap pin) and gnd. gnd 10, 13, 18, 23 13, 16, 21, 26 14, 17, 25, 32 18, 21, 29, 36 ground. tie all four pins together. cap 11 14 15 19 charge pump capacitor for generated negative supply voltage. connect a 220nf capacitor between cap and sw. sw 14 17 18 22 switch pin. connect 10h inductor between sw and v cc . a 22 25 29 33 rs485 positive receiver input (full-duplex mode) or rs232 receiver input 1 (ltc2870). b 21 24 28 32 rs485 negative receiver input (full-duplex mode) or rs232 receiver input 2 (ltc2870). ra 2 5 rs485 differential receiver output or rs232 receiver output 1. rb 3 6 rs232 receiver output 2. ro 34 38 rs485 differential receiver output. rin1 31 35 rs232 receiver input 1. rin2 30 34 rs232 receiver input 2. rout1 2 6 rs232 receiver output 1. rout2 3 7 rs232 receiver output 2. din1 8 12 rs232 driver input 1. din2 9 13 rs232 driver input 2. typical performance characteristics rs232 driver outputs enabling and disabling v dd and v ee powering up v dd and v ee ripple 5v/div 2v/div 28701 g20 40s/div fen vdd vee 5v/div 28701 g19 40s/div top curves: fast enable j dx232 bottom curves: shutdown j dx232 fen = 1 fen = 0 dout1 dout2 dout1 dx232 dout2 10mv/div 28701 g21 40s/div fast enable mode, all drivers and receivers disabled. vdd ripple vee ripple t a = 25c, v cc = v l = 3.3v, unless otherwise noted.
ltc2870/ltc2871 10 28701f pin functions pin name ltc2870 qfn ltc2870 tssop ltc2871 qfn ltc2871 tssop description dout1 23 27 rs232 driver output 1. dout2 22 26 rs232 driver output 2. di 7 11 rs485 driver input. dy 7 10 rs485 driver input or rs232 driver input 1. dz 8 11 rs232 driver input 2. y 19 22 26 30 rs485 positive driver output. rs232 driver output 1 (ltc2870). rs485 positive receiver input (ltc2870 or ltc2871 in half-duplex mode). z 17 20 24 28 rs485 negative driver output or rs232 driver output 2 (ltc2870). rs485 negative receiver input (ltc2870 or ltc2871 in half-duplex mode). 485/ 232 4 7 interface select input. a logic low enables rs232 mode and a high enables rs485 mode. the mode determines which transceiver inputs and outputs are accessible at the ltc2870 pins as well as which is controlled by the driver and receiver enable pins. rxen 5 8 receiver enable. a logic high disables rs232 and rs485 receivers leaving receiver outputs hi-z. a logic low enables the rs232 or rs485 receivers, depending on the state of the interface select input 485/ 232 . dxen 6 9 driver enable. a logic low disables the rs232 and rs485 drivers leaving the driver output in a hi-z state. a logic high enables the rs232 or rs485 drivers, depending on the state of the interface select input 485/ 232 . rx232 11 15 rs232 receiver enable. a logic high disables the rs232 receivers and input termination resistors leaving the rs232 receiver outputs in a hi-z state. a logic low enables the rs232 receivers and resistors, subject to the state of the ch2 pin. rx485 5 9 rs485 receiver enable. a logic high disables the rs485 receiver leaving the rs485 receiver output in a hi-z state. a logic low enables the rs485 receiver and resistors, subject to the state of the ch2 pin. dx232 10 14 rs232 driver enable. a logic low disables the rs232 drivers leaving the rs232 driver outputs in a hi-z state. a logic high enables the rs232 drivers. dx485 6 10 rs485 driver enable. a logic low disables the rs485 driver leaving the rs485 driver output in a hi-z state. a logic high enables the rs485 driver. h/ f 27 2 37 3 rs485 half-duplex select input. a logic low is used for full-duplex operation where pins a and b are the receiver inputs and pins y and z are the driver outputs. a logic high is used for half-duplex operation where pins y and z are both the receiver inputs and driver outputs and pins a and b do not serve as the receiver inputs. the impedance on a and b and state of differential termination between a and b is independent of the state of h/ f . the h/ f pin has no effect on rs232 operation. te485 28 3 38 4 rs485 termination enable. a logic high enables a 120 resistor between pins a and b and also between pins y and z. a logic low opens the resistors, leaving a/b and y/z unterminated. the ltc2870 termination resistors are never enabled in rs232 mode. fen 9 12 13 17 fast enable. a logic high enables fast enable mode. in fast enable mode the integrated dc/dc converter is active independent of the state of driver, receiver, and termination enable pins allowing faster circuit enable times than are otherwise possible. a logic low disables fast enable mode leaving the state of the dc/dc converter dependent on the state of driver, receiver, and termination enable control inputs. the dc/dc converter powers down only when fen is low and all drivers, receivers, and terminators are disabled (refer to table 1). lb 26 1 36 2 loopback enable. a logic high enables logic loopback diagnostic mode, internally routing the driver input logic levels to the receiver output pins. this applies to both rs232 channels as well as the rs485 driver/receiver. the targeted receiver must be enabled for the loopback signal to be available on its output. a logic low disables loopback mode. in loopback mode, signals are not inverted from driver inputs to receiver outputs. ch2 4 8 rs232 channel 2 disable. a logic high disables rs232 receiver 2 and rs232 driver 2 independent of the state of rx232 and dx232 pins. in this state, the disabled driver output becomes hi-z and the 5k load resistor on the disabled receiver input is opened. a logic low allows both rs232 transceiver channels to be enabled or disabled together based on the rx232 and dx232 pins.
ltc2870/ltc2871 11 28701f block diagram ltc2870 2870 bd control logic drivers receivers loopback path 0.1f dxen rxen te485 h/ f 485/ 232 fen lb dy dz ra rb gnd b a z y v ee v dd 1.7v to 5.5v ( v cc ) pulse-skipping boost regulator f = 1.2mhz rt232 rt485 2.2f 10h 220nf 3v to 5.5v 1f 1f cap sw v cc v l 232 485 232 232 485 232 5k rt232 rt485 125k 5k 125k 125k 120 rt485 120 h/ f 125k
ltc2870/ltc2871 12 28701f block diagram ltc2871 2871 bd control logic drivers receivers loopback path 0.1f dx232 dx485 rx232 rx485 te485 h/ f ch2 din1 din2 ro rout2 gnd rin2 rin1 z y dout1 dout2 v ee v dd 1.7v to 5.5v ( v cc ) fen lb rt232 rt485 2.2f 10h 220nf 3v to 5.5v di rout1 a b 1f 1f cap sw v cc v l 232 485 232 232 485 232 5k rt232 rt485 5k 120 rt485 120 h/ f 125k 125k 125k 125k pulse-skipping boost regulator f = 1.2mhz
ltc2870/ltc2871 13 28701f test circuits figure 1. rs485 driver dc characteristics figure 2. rs485 driver output current figure 3. rs485 receiver input current and resistance (note 5) figure 4. rs485 driver timing measurement 28701 f01 driver dy/di gnd or v l y r l r l z v od + C v oc + C 28701 f02 driver y or z dy/di gnd or v l z or y v out i ozd485 , i osd485 + C 28701 f03 receiver a or b b or a v in i in485 r in485 = v in i in485 + C 28701 f04 driver dy/di y z r diff c l c l t plhd485 t skewd485 t plhd485 t rd485 t fd485 90% 0v v od ?v od v l 0v dy/di y, z y - z 10% 90% 0v 10%
ltc2870/ltc2871 14 28701f test circuits figure 5. rs485 driver enable and disable timing measurements figure 6. rs485 receiver propagation delay measurements (note 5) figure 7. rs485 receiver enable and disable timing measurements (note 5) 28701 f05 t zld485 , t zlsd485 t lzd485 t hzd485 t zhd485 , t zhsd485 ?v cc ?v cc v l v ol v cc v oh 0v 0v 0.5v dxen/ dx485 y or z z or y driver dy/di dxen/dx485 v l or gnd y r l z gnd or v cc v cc or gnd r l c l c l ?v l 0.5v ?v l 28701 f06 receiver v cm v ab /2 a b ra/ro v ab /2 c l t plhr485 t skewr485 = t plhr485 C t phlr485 t rr485 90% 0v ?v l a-b ra/ro 10% t phlr485 t fr485 90% 0v Cv ab v ab ?v l 10% v l 28701 f07 t zlr485 t lzr485 t hzr485 t zhr485 ?v l ?v l v l v ol v l v oh 0v 0v 0.5v rxen / rx485 ra/ro ra/ro receiver ra/ro rxen / rx485 0v to 3v 3v to 0v a r l b v l or gnd c l ?v l 0.5v ?v l
ltc2870/ltc2871 15 28701f test circuits figure 8. rs485 termination resistance and timing measurements (note 5) figure 9. rs232 driver timing and slew rate measurements figure 10. rs232 driver enable and disable times 28701 f08 receiver v ab a b v ab i a r term = v b ?v l ?v l te485 i a i a 90% 10% t rtz485 t rten485 0v v l te485 + C + C 28701 f09 driver input driver output c l r l t phld232 t plhd232 t skewd232 = |t phld232 C t plhd232 | t f t r driver input driver input slew rate = 6v t f or t r 3v C3v 0v v old v l ?v l ?v l 0v 3v C3v 0v v ohd 28701 f10 0v or v l dxen/dx232 driver output c l r l t hzd232 t lzd232 dxen/ dx232 driver output driver output 0.5v t zhd232 t zld232 5v 5v 0.5v 0v 0v 0v v ohd v l ?v l ?v l v old
ltc2870/ltc2871 16 28701f test circuits figure 11. rs232 receiver timing measurements figure 12. rs232 receiver enable and disable times 28701 f11 t phlr232 t skewr232 = |t plhr232 C t phlr232 | t plhr232 t rr232 90% 1.5v 1.5v ?v l 10% t fr232 90% C3v v l +3v ?v l 10% 0v receiver output receiver output receiver input receiver input c l 28701 f12 C3v or +3v rxen / rx232 receiver output gnd or v l c l r l t hzr232 t lzr232 rxen / rx232 receiver output receiver output 0.5v t zhr232 t zlr232 ?v l ?v l 0.5v 0v 0v v l v ohr v l ?v l ?v l v olr
ltc2870/ltc2871 17 28701f function tables table 1. ltc2870 mode selection table fen 485/ 232 rxen dxen te485 h/ f lb dc/dc converter mode and comments 0 x 1 0 0 x x off low power shutdown: all main functions off 0 0 1 0 x x x off low power shutdown: all main functions off 1 x 1 0 0 x x on fast-enable: dc/dc converter on only x 0 x 1 x x 0 on rs232 drivers on x 0 0 x x x 0 on rs232 receivers on x 1 x 1 x x 0 on rs485 driver on x 1 0 x x x 0 on rs485 receiver on x 1 x x 1 x x on rs485 driver and receiver 120 termination enabled x 1 x x x 0 0 x rs485 full-duplex mode x 1 x x x 1 0 x rs485 half-duplex mode x 1 0 x x x 1 on rs485 loopback mode x 0 0 x x x 1 on rs232 loopback mode table 2. ltc2871 mode selection table ( ch2 = 0) fen rx232 dx232 rx485 dx485 te485 h/ f lb dc/dc converter mode and comments 0 1 0 1 0 0 x x off low power shutdown: all main functions off 1 1 0 1 0 0 x x on fast-enable: dc/dc converter on only x x 1 x x x x 0 on rs232 drivers on x 0 x x x x x 0 on rs232 receivers on x x x x 1 x x 0 on rs485 driver on x x x 0 x x x 0 on rs485 receiver on x x x x x x 0 0 x rs485 full-duplex mode x x x x x x 1 0 x rs485 half-duplex mode x x x 0 x x x 1 on rs485 loopback mode x 0 x x x x x 1 on rs232 loopback mode table 3. rs232 receiver mode (485/ 232 = 0 for ltc2870, ch2 = 0 for ltc2871) rx232 or rxen receiver inputs (a, b, rin1, rin2) conditions receiver outputs (ra, rb, rout1, rout2) ltc2870 receiver inputs (a, b) ltc2871 receiver inputs (rin1, rin2) 1 x no fault hi-z 125k hi-z 0 0 no fault 1 5k 5k 0 1 no fault 0 5k 5k 0 x thermal fault hi-z 5k 5k table 4. rs232 driver mode (485/ 232 = 0 for ltc2870, ch2 = 0 for ltc2871) dx232 or dxen driver inputs (dy, dz, din1, din2) conditions ltc2870 driver outputs (y, z) ltc2871 driver outputs (dout1, dout2) 0 x no fault 125k hi-z 1 0 no fault 1 1 1 1 no fault 0 0 x x thermal fault 125k hi-z
ltc2870/ltc2871 18 28701f function tables table 5. ltc2871 ch2 control ch2 dx232 rx232 rs232 receiver inputs rs232 driver outputs comments rin1 rin2 dout1 dout2 x 0 1 hi-z hi-z hi-z hi-z both drivers and receivers disabled 0 0 0 5k 5k hi-z hi-z both receivers enabled, both drivers disabled 0 1 1 hi-z hi-z driven driven both receivers disabled, both drivers enabled 0 1 0 5k 5k driven driven both receivers and drivers enabled 1 0 0 5k hi-z hi-z hi-z channel 2 drivers and receivers disabled 1 1 1 hi-z hi-z driven hi-z channel 2 drivers and receivers disabled 1 1 0 5k hi-z driven hi-z channel 2 drivers and receivers disabled table 6. rs485 driver mode (te485 = 0) dx485 or dxen di conditions y z 0 x no fault 125k 125k 1 0 no fault 0 1 1 1 no fault 1 0 x x thermal fault 125k 125k table 7. rs485 receiver mode (lb = 0) rxen or rx485 a - b (note 5) conditions ra, ro 1 x no fault hi-z 0 < C200mv no fault 0 0 > 200mv no fault 1 0 inputs open or shorted together (dc) failsafe 1 x x thermal fault hi-z table 8. rs485 termination (485/ 232 = 1 for ltc2870) te485 h/ f , lb conditions r (a to b) r (y to z) 0 x no fault hi-z hi-z 1 x no fault 120 120 x x thermal fault hi-z hi-z table 9. rs485 duplex control (485/ 232 = 1 for ltc2870) h/ f rs485 driver outputs rs485 receiver inputs 0 y, z a, b 1 y, z y, z table 10. ltc2870 loopback functions lb rxen mode 0 x not loopback x 1 not loopback 1 0 loopback (ra = dy, rb = dz) table 11. ltc2871 loopback functions lb rx232 rx485 mode 0 x x not loopback x 1 1 not loopback 1 0 1 loopback rs232 (rout1 = din1, rout2 = din2) 1 1 0 loopback rs485 (r0 = di) 1 0 0 loopback all (rout1 = din1, rout2 = din2, ro = di)
ltc2870/ltc2871 19 28701f overview the ltc2870 and ltc2871 are flexible multiprotocol trans- ceivers supporting rs485/rs422 and rs232 protocols. these parts can be powered from a single 3v to 5.5v supply with optional logic interface supply as low as 1.7v. an integrated dc/dc converter provides the positive and negative supply rails needed for rs232 operation. auto- matically selected integrated termination resistors for both rs232 and rs485 protocols are included, eliminating the need for external components and switching relays. both parts include loopback control for self-test and debug as well as logically-switchable half- and full-duplex control of the rs485 bus interface. the ltc2870 offers a single port that can be configured as either two rs232 receivers and drivers or one rs485/ rs422 receiver and driver depending on the state of the 485/ 232 pin. control inputs dxen and rxen provide independent control of driver and receiver operation for either rs232 or rs485 transceivers, depending on the selected operating protocol. the ltc2871 separates the rs232 and rs485 transceivers into independent i/os allowing simultaneous operation of two rs232 transceivers and one rs485 transceiver. independent control over driver and receiver mode for each protocol is provided with logic inputs dx232, rx232 , dx485, rx485 . single channel rs232 operation is possible via the ch2 control pin. the disabled channel maintains a hi-z state on the receiver input and driver output, allowing these lines to be shared with other transceivers. both parts feature rugged operation with esd ratings of 26kv (ltc2870) and 16kv (ltc2871) 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 v cc input, generating a 7v v dd supply and a charge pumped C6.3v v ee supply, as shown in figure 13. v dd and v ee 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 10h inductor (l1) and a bypass capacitor (c4) of 2.2f. the charge pump capacitor (c1) is 220nf and the storage capacitors (c2 and c3) are 1f. larger storage capacitors up to 4.7f may be used if c1 and c4 are scaled proportionately. locate c1Cc4 close to their associated pins. up to two ltc2870 or ltc2871 devices can be powered from one of the devices; see figure 48 in the typical ap- plications section. inductor selection a 10h inductor with a saturation current (i sat ) rating of at least 220ma and a dcr (copper wire resistance) of less than 1.3 is required. some small inductors meeting these requirements are listed in table 12. table 12. recommended inductors part number i sat (ma) max dcr () size(mm) manufacturer lbc2016t100k cbc2016t100m 245 380 1.07 1.07 2 1.6 1.6 2 1.6 1.6 taiyo yuden www.t-yuden.com fslb2520-100k 220 1.1 2.5 2 1.6 toko www.tokoam.com capacitor selection the small size of ceramic capacitors makes them ideal for the ltc2870 and ltc2871. use x5r or x7r dielectric types; their esr is low and they retain their capacitance over relatively wide voltage and temperature ranges. use a voltage rating of at least 10v. applications information figure 13. dc/dc converter 28701 f13 3v to 5.5v c1 220nf l1 10h c4 2.2f v cc v dd v ee sw cap c2 1f c3 1f pulse-skipping boost regulator f = 1.2mhz
ltc2870/ltc2871 20 28701f inrush current and supply overshoot precaution in certain applications fast supply slew rates are generated when power is connected. if the v cc voltage is greater than 4.5v and its rise time is faster than 10s, the pins v dd and sw can exceed their absolute maximum values during start-up. when supply voltage is applied to v cc , the voltage difference between v cc and v dd generates inrush current flowing through inductor l1 and capacitors c1 and c2. the peak inrush current must not exceed 2a. to avoid this condition, add a 1 resistor as shown in figure 14. this precaution is not relevant for supply voltages below 4.5v or rise times longer than 10s. v l logic supply and logic pins a separate logic supply pin v l allows the ltc2870 and ltc2871 to interface with any logic signal from 1.7v to 5.5v. all logic i/os use v l as their high supply. for proper operation, v l should not be greater than v cc . during power-up, if v l is higher than v cc , the device will not be damaged, but behavior of the device is not guaranteed. if v l is not connected to v cc , bypass v l with a 0.1f capacitor to gnd. rs232 and rs485 driver outputs are undriven and the rs485 termination resistors are disabled when v l or v cc is grounded or v cc is disconnected. although all logic input pins reference v l as their high supply, they can be driven up to 7v, independent of v l and v cc , with the exception of fen, which must not exceed v l by more than 1v for proper operation. logic input pins do not have internal biasing devices to pull them up or down. they must be driven high or low to establish valid logic levels; do not float. rs485 driver the rs485 driver provides full rs485/rs422 compati- bility. when enabled, if di is high, y C z is positive. with the driver disabled the y and z output resistance is greater than 96k (typically 125k) to ground over the entire common mode range of C7v to +12v. this resistance is equivalent to the input resistance on these lines when the driver is configured in half-duplex mode and y and z act as the rs485 receiver inputs. driver overvoltage and overcurrent protection the rs232 and rs485 driver outputs are protected from short circuits to any voltage within the absolute maximum range 15v. the maximum current in this condition is 90ma for the rs232 driver and 250ma for the rs485 driver. if the rs485 driver output is shorted to a voltage greater than v cc , when it is active, positive current of up to 100ma may flow from the driver output back to v cc . if the system power supply or loading cannot sink this excess current, clamp v cc to gnd with a zener diode (e.g., 5.6v, 1w, 1n4734) to prevent an overvoltage condition on v cc . applications information figure 14. supply current overshoot protection for input supplies of 4.5v of higher 28701 f14 0v 5v 10s c1 220nf l1 10h inrush current c4 2.2f r1 1 1/8w v cc v dd gnd sw cap c2 1f
ltc2870/ltc2871 21 28701f figure 15. rs485 receiver input threshold characteristics applications information all devices also feature thermal shutdown protection that disables the drivers, receivers, and rs485 terminators in case of excessive power dissipation (see note 6). rs485 balanced receiver with full failsafe operation the ltc2870 and ltc2871 receivers use a window com- parator with two voltage thresholds centered around zero for low pulse width distortion. as illustrated in figure 15, for a differential signal approaching from a negative direction, the threshold is typically +65mv. when approaching from the positive direction, the threshold is typically C65mv. each of these thresholds has about 25mv of hysteresis (not shown in the figure). the state of ro reflects the polarity of aCb in full-duplex mode or yCz in half-duplex mode. this windowing around 0v preserves pulse width and duty cycle for small input signals with heavily slewed edges, typical of what might be seen at the end of a very long cable. this performance is highlighted in figure 16, where a signal is driven through 4000 feet of cat5e cable at 3mbps. even though the differential signal peaks at just over 100mv and is heavily slewed, the output maintains a nearly perfect signal with almost no duty cycle distortion. an additional benefit of the window comparator architecture is excellent noise immunity due to the wide effective dif- ferential hysteresis (or ac hysteresis) of about 130mv for normal signals transitioning through the window region in less than approximately 2s. increasingly slower signals will have increasingly less effective hysteresis, limited by the dc failsafe value of about 25mv. the ltc2870 and ltc2871 provide full failsafe operation that guarantees the receiver output will be a logic high state when the inputs are shorted, left open, or terminated but not driven, for more than about 2s. the delay allows normal data signals to transition through the threshold region without being interpreted as a failsafe condition. rs485 biasing resistors not required rs485 networks are often biased with a resistive divider to generate a differential voltage of 200mv on the data lines, which establishes a logic high state when all the transmitters on the network are disabled. the values of the biasing resistors depend on the number and type of transceivers on the line and the number and value of terminating resistors. therefore the values of the biasing resistors must be customized to each specific network installation, and may change if nodes are added to or removed from the network. the internal failsafe feature of the ltc2870 and ltc2871 eliminates the need for external biasing resistors. the ltc2870 and ltc2871 transceivers will operate correctly on unbiased, biased or underbiased networks. 28701 f15 receiver output low C200mv C65mv 0v ro 65mv 200mv v ab receiver output high figure 16. a 3mbps signal driven down 4000ft of cat 5e cable. top traces: received signals after transmission through cable; middle trace: math showing differences of top two signals; bottom trace: receiver output 0.1v/div 0.1v/div 5v/div 28701 f16 200ns/div ro (a-b) a b
ltc2870/ltc2871 22 28701f applications information receiver outputs the rs232 and rs485 receiver outputs are internally driven high (to v l ) or low (to gnd) with no external pull- up needed. when the receivers are disabled the output pin becomes hi-z with leakage of less than 5a for voltages within the v l supply range. rs485 receiver input resistance the rs485 receiver input resistance from a or b to gnd (y or z to gnd in half-duplex mode with driver disabled) is greater than 96k (typically 125k) when the integrated termination is disabled. this permits up to a total of 256 receivers per system without exceeding the rs485 receiver loading specification. the input resistance of the receiver is unaffected by enabling/disabling the receiver or whether the part is in half-duplex, full-duplex, loopback mode, or even unpowered. the equivalent input resistance looking into the rs485 receiver pins is shown in figure 17. figure 18. typical resistance of the enabled rs485 terminator vs common mode voltage on a /b through logic control, the proper line termination for cor- rect operation when configuring transceiver networks. termination should be enabled on transceivers positioned at both ends of the network bus. termination on the driver nodes is important for cases where the driver is disabled but there is communication on the connecting bus from another node. differential termination resistors are never enabled in rs232 mode on the ltc2870. when the te485 pin is high, the termination resistors are enabled and the differential resistance from a to b and y to z is 120. the resistance is maintained over the entire rs485 common mode range of C7v to 12v as shown in figure 18. figure 17: equivalent rs485 receiver input resistance into a and b (note 5) 28701 f17 a b te485 60 60 125k 125k selectable rs485 termination proper cable termination is important for good signal fidel- ity. when the cable is not terminated with its characteristic impedance, reflections cause waveform distortion. the ltc2870 and ltc2871 offer integrated switchable 120 termination resistors between the differential receiver inputs and also between the differential driver outputs. this provides the advantage of being able to easily change, rs485 half- and full-duplex control the ltc2870 and ltc2871 are equipped with a control to switch between half- and full-duplex operation. with the h/ f pin set to a logic low, the a and b pins serve as the differential receiver inputs. with the h/ f pin set to a logic high, the y and z pins serve as the differential inputs. in either configuration, the rs485 driver outputs are always on y and z. the impedance looking into the a and b pins is not affected by h/ f control, including the differential termination resistance. the h/ f control does not affect rs232 operation. voltage (v) C10 resistance () 126 124 122 118 120 116 10 C5 28701 f18 15 5 0 v cc = 5.0v v cc = 3.3v
ltc2870/ltc2871 23 28701f applications information logic loopback a loopback mode connects the driver inputs to the re- ceiver outputs (non-inverting) for self test. this applies to both rs232 and rs485 transceivers. loopback mode is entered when the lb pin is high and the relevant receiver is enabled. in loopback mode, the drivers function normally. they can be disabled with outputs in a hi-z state or left enabled to allow loopback testing in normal operation. loopback works in half- or full-duplex mode and does not affect the termination resistors. data rate (bps) cable length (ft) 28701 f19 10k 1k 100 10 10k 10m 100m 1m 100k ltc2870/ltc2871 max data rate rs485/rs422 max data rate figure 19. cable length vs data rate (rs485/rs422 standard shown in vertical solid line) the solid vertical line represents the specified maximum data rate in the rs485/rs422 standards. the dashed lines at 20mbps show the maximum data rates of the ltc2870 and ltc2871. layout considerations all v cc pins must be connected together on the pc board with very low impedance traces or with a dedicated plane. a 2.2f or larger decoupling capacitor (c4 in figure 13) must be placed less than 0.7cm away from the v cc pin that is adjacent to the v dd pin. 0.1f capacitors to gnd can be added on the v cc pins adjacent to the b and v l pins if the connection to the 2.2f decoupling capacitor is not direct or if the trace is very narrow. all gnd pins must be connected together and all v ee pins must be connected together, including the exposed pad on the bottom of the package. the bypass capacitor at v ee , c3, should be positioned closest to the v ee pin that is adjacent to the cap pin, with no more than 1cm of total trace length between the v ee and gnd pins. place the charge pump capacitor, c1, directly adjacent to the sw and cap pins, with no more than one centimeter of total trace length to maintain low inductance. close placement of the inductor, l1, is of secondary importance compared to the placement of c1 but should include no more than two centimeters of total trace length. the pc board traces connected to high speed signals a/b and y/z should be symmetrical and as short as possible to minimize capacitive imbalance and maintain good dif- ferential signal integrity. to minimize capacitive loading effects, the differential signals should be separated by more than the width of a trace. route outputs away from sensitive inputs to reduce feedback effects that might cause noise, jitter, or even oscillations. for example, do not route di or a/b near the driver or receiver outputs. rs485 cable length vs data rate for a given data rate, the maximum transmission dis- tance is bounded by the cable properties. a typical curve of cable length vs data rate compliant with the rs485/ rs422 standards is shown in figure 19. three regions of this curve reflect different performance limiting fac- tors in data transmission. in the flat region of the curve, maximum distance is determined by resistive losses in the cable. the downward sloping region represents limits in distance and data rate due to ac losses in the cable.
ltc2870/ltc2871 24 28701f typical applications figure 20. ltc2870 in rs232 mode figure 21. ltc2870 in rs232 mode with loopback figure 22. ltc2870 in rs485 mode, terminated figure 23. ltc2870 in rs485 mode in loopback figure 24. ltc2870 in rs485 mode half-duplex figure 25. ltc2870 in rs485 mode, half-duplex, with loopback and terminated 28701 f20 dxen v l lb 485/ 232 rxen dy rb gnd dz ra y b z a ltc2870 28701 f21 485/ 232 rxen dy rb gnd dz ra y b z a ltc2870 dxen lb v l 28701 f23 dxen v l rxen h/ f te485 485/ 232 lb dy gnd ra y b z a ltc2870 28701 f22 dxen v l rxen h/ f lb 485/ 232 te485 dy gnd ra 120 y b z a ltc2870 120 28701 f24 dxen v l rxen te485 lb 485/ 232 h/ f dy gnd ra y z ltc2870 28701 f25 dxen 485/ 232 h/ f lb te485 v l rxen dy 120 120 gnd ra y b z a ltc2870 v cc = 3v to 5.5v, v l = 1.7v to v cc . logic input pins not shown are tied to a valid logic state.
ltc2870/ltc2871 25 28701f typical applications figure 26. ltc2870 protocol switching figure 27. ltc2871 in rs485 mode figure 28. ltc2871 in rs232 mode figure 29. ltc2871 single rs232 channel active figure 30. ltc2871 in rs485 and rs232 mode figure 31. ltc2871 in rs485 and rs232 mode with loopback and rs485 termination 28701 f26 dxen 485/ 232 v l lb rxen h/ f rb gnd ra b a ltc2870 dz dy z 120 120 y rs 485 rs 232 te485 28701 f27 v l ch2 dx232 te485 h/ f rx485 rx232 dx485 gnd ro b a ltc2871 lb di z y 28701 f28 v l ch2 dx485 te485 h/ f rx232 gnd ltc2871 lb din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 rx485 dx232 28701 f29 v l dx485 te485 h/ f rx232 rx485 ch2 dx232 gnd ltc2871 lb din1 rout1 dout1 rin1 28701 f30 dx232 dx485 v l rx485 rx232 te485 h/ f ch2 gnd ltc2871 lb din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 ro b a di z y 28701 f31 dx485 dx232 lb te485 v l rx485 rx232 h/ f ch2 gnd ltc2871 din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 ro b a di z y 120 120 v cc = 3v to 5.5v, v l = 1.7v to v cc . logic input pins not shown are tied to a valid logic state.
ltc2870/ltc2871 26 28701f figure 32. ltc2871 in rs485 and rs232 mode, both half-duplex figure 33. ltc2871 in rs485 and rs232 mode, rs485 half-duplex, loopback figure 34. ltc2871 in rs485 and rs232 mode, rs485 half-duplex, terminated figure 35. rs485 duplex switching figure 36. microprocessor interface figure 37. driving larger rs232 loads typical applications 28701 f32 dx485 h/ f v l ch2 te485 rx485 rx232 lb gnd ltc2871 dx232 d r 485 din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 ro di z y d r 232 28701 f33 dx232 dx485 lb h/ f v l rx485 rx232 te485 ch2 gnd ltc2871 din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 ro di z y 28701 f34 dx232 dx485 h/ f te485 v l rx232 rx485 ch2 lb gnd ltc2871 din1 rout2 din2 rout1 dout1 rin2 dout2 rin1 ro di 120 z y b a 120 28701 f35 485/ 232 te485 v l h/ f lb rb gnd ro b 120 a ltc2870/ ltc2871 h/ f di dy z 120 y half duplex rs485 full 28701 f36 3v to 5.5v 1.7v to v cc v cc v l gnd ltc2870/ ltc2871 dy, din1 rb, rout2 dz, din2 ra, rout1 y b z a control signals p 28701 f37 ltc2870/ ltc2871 rs232 c l 3k data rate 100kbps 500kbps c l 5nf 1nf v cc = 3v to 5.5v, v l = 1.7v to v cc . logic input pins not shown are tied to a valid logic state.
ltc2870/ltc2871 27 28701f typical applications figure 38. ltc2870: making use of shared i/o for various communication configurations figure 39. ltc2870: using external connections for half-duplex rs232 or rs485 operation 28701 f38 ltc2870 1.7v to v cc 3v to 5.5v 485/ 232 rxen dxen te485 h/ f dy y z a b dz ra rb v l v l controller connector v cc gnd rs485 rs485 full-duplex 485/ 232 = 1 h/ f = 0 rs485 half-duplex 485/ 232 = 1 h/ f = 1 rs232 full-duplex 485/ 232 = 0 h/ f = x rs485 rs485 rs485 rs485 rs485 rs232 rs232 rs232 rs232 28701 f39 ltc2870 1.7v to v cc 3v to 5.5v 485/ 232 rxen dxen h/ f dy y z a b dz ra rb v l v l controller connector v cc te485 gnd rs485 rs485 half-duplex 485/ 232 = 1 h/ f = 0 rs232 half-duplex 485/ 232 = 0 h/ f = x rs485 rs232 rs232
ltc2870/ltc2871 28 28701f figure 40. ltc2871: various communication configurations figure 41. ltc2871: more communication configurations using external connections typical applications 28701 f40 ltc2871 1.7v to v cc 3v to 5.5v dx485 rx232 rx485 dx232 te485 h/ f din1 din2 y dout1 dout2 z a b rin2 rin1 di rout1 ro rout2 v l v l v cc gnd rs485 rs232 full-duplex rs485 full-duplex h/ f = 0 rs232 full-duplex rs485 half-duplex h/ f = 1 rs485 rs485 rs232 rs232 rs232 rs232 controller rs232 rs232 rs485 rs485 connector rs232 rs232 rs485 28701 f41 ltc2871 1.7v to v cc 3v to 5.5v din1 din2 y dout1 dout2 z a b rin2 rin1 di rout1 ro rout2 v l v l v cc gnd rs485 rs232 half-duplex rs485 full-duplex h/ f = 0 rs232 half-duplex rs485 half-duplex h/ f = 1 rs485 rs485 rs232 rs232 rs232 rs232 controller rs485 rs485 connector rs485 dx485 rx232 rx485 dx232 te485 h/ f
ltc2870/ltc2871 29 28701f figure 42. rs232 extension cord using rs232 to rs485 conversion figure 43. rs485 full-duplex network typical applications 28701 f42 dx232 dx485 ch2 te485 v l rx485 rx232 h/ f lb rx485 rx232 h/ f lb gnd gnd ltc2871 ltc2871 v l dx232 dx485 ch2 te485 rin1 ro din1 rout1 rxin rs485 up to 4000 ft cat5e cable rs232 driver out rxout rs232 driver in b a rout1 di dout1 di rout1 rin1 din1 ro 120 120 z y 120 120 b a z y 28701 f43 ltc2870/ltc2871 120 ltc2852 slave slave master ltc2855 120 te485 te v l 3.3v 120 ltc2852 slave v cc = 3v to 5.5v, v l = 1.7v to v cc . logic input pins not shown are tied to a valid logic state.
ltc2870/ltc2871 30 28701f figure 46. rs485 receiver with multiplexed inputs typical applications figure 44. rs232 triple transceiver with selectable line interface figure 45. rs232 triple transceiver with selectable logic interface 28701 f44 din1 rout2 din2 rout1 dout1 port 1 logic interface port 2a/2b logic interface select line 2a select line 2b port 1 line interface port 2a line interface rin2 dout2 rin1 ltc2871 din2 ch2 ch2 rout1 din1 rout2 dout2 port 3 logic interface port 2b line interface port 3 line interface rin1 dout1 rin2 ltc2871 28701 f45 din1 rout2 din2 rout1 dout1 port 1 logic interface port 2a logic interface select line 2a select line 2b port 1 line interface port 2a/2b line interface rin2 dout2 rin1 ltc2871 port 2b logic interface din2 ch2 ch2 rout1 din1 rout2 dout2 port 3 logic interface port 3 line interface rin1 dout1 rin2 ltc2871 28701 f46 h/ f ra, ro rs485 interface input1 input2 y z a b ltc2870/ ltc2871 select input2 input1
ltc2870/ltc2871 31 28701f typical applications figure 47. typical supply connections with external components shown figure 48. running two ltc2870 or ltc2871 devices from one shared power source 28701 f48 3v to 5.5v v l v cc sw 22h 470nf cap gnd v dd v ee ltc2870/ ltc2871 sw cap v cc v ee v l v dd gnd ltc2870/ ltc2871 2.2f 2.2f 2.2f inductor: taiyo yuden cbc2518t220m, murata lqh32cn220k53 28701 f47 3v to 5.5v 3v to 5.5v 1.7v to v cc te485 v l v dd v ee v cc sw rs485 interface 10h 10h 220nf 220nf cap h/ f gnd ltc2871 ltc2870 gnd v cc 485/ 232 h/ f v l v dd v ee te485 dy ra sw ro din1 rout1 cap b a din2 rout2 1f dout1 rin1 dout2 rin2 rs232 interface di 120 z y b a z y 120 120 120 2.2f 1f 2.2f 0.1f 1.7v to v cc 0.1f 1f 1f
ltc2870/ltc2871 32 28701f package description fe package 28-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1663) exposed pad variation eb fe28 (eb) tssop 0204 0.09 ?0.20 (.0035 ?.0079) 0 ?8 0.25 ref 0.50 ?0.75 (.020 ?.030) 4.30 ?4.50* (.169 ?.177) 134 5 6 7 8910 11 12 13 14 19 20 22 21 15 16 18 17 9.60 ?9.80* (.378 ?.386) 4.75 (.187) 2.74 (.108) 28 2726 25 24 23 1.20 (.047) max 0.05 ?0.15 (.002 ?.006) 0.65 (.0256) bsc 0.195 ?0.30 (.0077 ?.0118) typ 2 recommended solder pad layout exposed pad heat sink on bottom of package 0.45 0.05 0.65 bsc 4.50 0.10 6.60 0.10 1.05 0.10 4.75 (.187) 2.74 (.108) millimeters (inches) *dimensions do not include mold flash. mold flash shall not exceed 0.150mm (.006") per side note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale see note 4 4. recommended minimum pcb metal size for exposed pad attachment 6.40 (.252) bsc
ltc2870/ltc2871 33 28701f package description fe package 38-lead plastic tssop (4.4mm) (reference ltc dwg # 05-08-1772 rev a) exposed pad variation aa 4.75 (.187) ref fe38 (aa) tssop 0608 rev a 0.09 C 0.20 (.0035 C .0079) 0 o C 8 o 0.25 ref 0.50 C 0.75 (.020 C .030) 4.30 C 4.50* (.169 C .177) 1 19 20 ref 9.60 C 9.80* (.378 C .386) 38 1.20 (.047) max 0.05 C 0.15 (.002 C .006) 0.50 (.0196) bsc 0.17 C 0.27 (.0067 C .0106) typ recommended solder pad layout 0.315 0.05 0.50 bsc 4.50 ref 6.60 0.10 1.05 0.10 4.75 ref 2.74 ref 2.74 (.108) millimeters (inches) *dimensions do not include mold flash. mold flash shall not exceed 0.150mm (.006") per side note: 1. controlling dimension: millimeters 2. dimensions are in 3. drawing not to scale see note 4 4. recommended minimum pcb metal size for exposed pad attachment 6.40 (.252) bsc
ltc2870/ltc2871 34 28701f package description ufd package 28-lead plastic qfn (4mm 5mm) (reference ltc dwg # 05-08-1712 rev b) 4.00 0.10 (2 sides) 2.50 ref 5.00 0.10 (2 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wxxx-x). 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 27 28 1 2 bottom view?xposed pad 3.50 ref 0.75 0.05 r = 0.115 typ r = 0.05 typ pin 1 notch r = 0.20 or 0.35 45 chamfer 0.25 0.05 0.50 bsc 0.200 ref 0.00 ?0.05 (ufd28) qfn 0506 rev b recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 2.50 ref 3.50 ref 4.10 0.05 5.50 0.05 2.65 0.05 3.10 0.05 4.50 0.05 package outline 2.65 0.10 3.65 0.10 3.65 0.05
ltc2870/ltc2871 35 28701f information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description uhf package 38-lead plastic qfn (5mm 7mm) (reference ltc dwg # 05-08-1701 rev c) 5.00 p 0.10 note: 1. drawing conforms to jedec package outline m0-220 variation whkd 2. drawing not to scale 3. all dimensions are in millimeters pin 1 top mark (see note 6) 37 1 2 38 bottom viewexposed pad 5.50 ref 5.15 0.10 7.00 p 0.10 0.75 p 0.05 r = 0.125 typ r = 0.10 typ 0.25 p 0.05 (uh) qfn ref c 1107 0.50 bsc 0.200 ref 0.00 C 0.05 recommended solder pad layout apply solder mask to areas that are not soldered 3.00 ref 3.15 0.10 0.40 p 0.10 0.70 p 0.05 0.50 bsc 5.5 ref 3.00 ref 3.15 0.05 4.10 p 0.05 5.50 p 0.05 5.15 0.05 6.10 p 0.05 7.50 p 0.05 0.25 p 0.05 package outline 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.20mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 notch r = 0.30 typ or 0.35 s 45 o chamfer
ltc2870/ltc2871 36 28701f linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2010 lt 1210 ? printed in usa related parts typical application part number description comments ltc1334 single 5v rs232/rs485 multiprotocol transceiver dual port, single 5v supply, configurable, 10kv esd ltc1387 single 5v rs232/rs485 multiprotocol transceiver single port, configurable ltc2801/ltc2802/ ltc2803/ltc2804 1.8v to 5.5v rs232 single and dual transceivers up to 1mbps, 10kv esd, logic supply pin, tiny dfn packages ltc2854/ltc2855 3.3v 20mbps rs485 transceiver with integrated switchable termination 3.3v supply, integrated, switchable, 120 termination resistor, 25kv esd ltc2859/ltc2861 20mbps rs485 transceiver with integrated switchable termination 5v supply, integrated, switchable, 120 termination resistor, 15kv esd ltm2881 complete isolated rs485/rs422 module transceiver + power 20mbps, 2500v rms isolation with integrated dc/dc converter, integrated, switchable, 120 termination resistor, 15kv esd ltm2882 dual isolated rs232 module transceiver + power 1mbps, 2500v rms isolation with integrated dc/dc converter, 10kv esd quad rs232 transceiver with rs485 communication over half-duplex, terminated bus 28701 ta02 3v to 5.5v 3.3v v l v cc sw 22h 470nf cap te485 ltc2871 ltc2854 ltc2804 gnd v cc te di ro v cc v l cap ro din1 rout1 b a din2 rout2 dout1 rin1 dout2 rin2 di 120 z y b a 120 120 2.2f 2.2f 2.2f 0.1f gnd v dd v ee t1in rout1 t2in rout2 t1out1 sw rin1 t2out rin2 gnd v dd v ee

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