LTC1387 Single 5V RS232/RS485 Multiprotocol Transceiver U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Two RS232 Transceivers or One RS485 Transceiver Operates from a Single 5V Supply Guaranteed Receiver Output with Inputs Floating or Shorted to Ground Logic Selectable Fast/Slow RS485 Driver Slew Rate Low Supply Current: 7mA Typical 5µA Supply Current in Shutdown Self-Testing Capability in Loopback Mode Separate Driver and Receiver Enable Controls Driver Maintains High Impedance in Three-State, Shutdown or with Power Off Receiver Inputs Can Withstand ±25V U APPLICATIONS ■ ■ ■ ■ ■ Point-of-Sale Terminals Software Selectable Multiprotocol Interface Ports Low Power RS485/RS422/RS232/EIA562 Interface Cable Repeaters Level Translators The LTC ®1387 is a low power reconfigurable CMOS bidirectional transceiver. It can be configured as an RS485 differential port or as two RS232 single-ended ports. An onboard charge pump uses four 0.1µF capacitors to generate boosted positive and negative supplies, allowing the RS232 drivers to meet ±5V output swing requirements with only a single 5V supply. A shutdown mode reduces the ICC supply current to 5µA. The RS232 transceivers are in full compliance with RS232 specification. The RS485 transceiver is in full compliance with RS485 and RS422 specifications. The RS485 receiver assumes a known output state when the inputs are floating or shorted to ground. All interface drivers feature short-circuit and thermal shutdown protection. An enable pin allows RS485 driver outputs to be forced into high impedance which is maintained even when the outputs are forced beyond supply rails or the power is off. A loop back mode allows the driver outputs to be connected back to the receiver inputs for diagnostic self-test. The LTC1387 is available in 20-pin plastic SSOP and SW packages. , LTC and LT are registered trademarks of Linear Technology Corporation. UO TYPICAL APPLICATI 2 1 20 19 19 20 1 3 LTC1387 LTC1387 2 3 18 VCC2 5V 18 VCC1 5V RECOUT 17 4 5 120Ω DR IN SLEW DR ENABLE 5V 15 4 5 RS485 INTERFACE 120Ω 6 6 7 14 9 8 12 13 11 10 7 4000-FT 24-GAUGE TWISTED PAIR 5V 5V 17 15 14 5V 5V 8 9 13 12 10 11 RECOUT DR IN SLEW DR ENABLE 5V ALL CAPACITORS: 0.1µF MONOLITHIC CERAMIC TYPE LTC1387 • TA01 1 LTC1387 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) ............................................. 6.5V Input Voltage Drivers ................................... – 0.3V to (VCC + 0.3V) Receivers ............................................. – 25V to 25V 485/232, ON, DXEN RXEN, SLEW ........................... – 0.3V to (VCC + 0.3V) Output Voltage Drivers ................................................. – 18V to 18V Receivers ............................... – 0.3V to (VCC + 0.3V) Short-Circuit Duration Output ........................................................ Indefinite VDD, VEE, C1+, C1–, C2+, C2– .......................... 30 sec Operating Temperature Range LTC1387C .............................................. 0°C to 70°C LTC1387I ........................................... – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................ 300°C ORDER PART NUMBER TOP VIEW C1+ 1 20 C2 + C1– 2 19 C2 – VDD 3 18 VCC LTC1387CG LTC1387CSW LTC1387IG LTC1387ISW A 4 17 RA B 5 16 RB Y 6 15 DY Z 7 14 DZ/SLEW 485/232 8 13 ON DXEN 9 12 RXEN GND 10 G PACKAGE 20-LEAD PLASTIC SSOP 11 VEE SW PACKAGE 20-LEAD PLASTIC SO TJMAX = 125°C, θJA = 120°C/W (G) TJMAX = 125°C, θJA = 75°C/W (SW) Consult factory for Military grade parts. DC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 Driver (485/232 = High, ON = DXEN = High) VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 ● VOD2 Differential Driver Output Voltage (With Load) Figure 1, R = 50Ω (RS422) Figure 1, R = 27Ω (RS485) ● ● 6 V 6 6 V V ∆VOD Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Figure 1, R = 27Ω or R = 50Ω ● 0.2 V VOC Driver Common Mode Output Voltage Figure 1, R = 27Ω or R = 50Ω ● 3 V ∆VOC Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Figure 1, R = 27Ω or R = 50Ω ● 0.2 V IOSD Driver Short-Circuit Current VO = – 7V, 12V; VO = High VO = – 7V, 12V; VO = Low (Note 4) ● ● 250 250 mA mA IOZD Three-State Output Current (Y, Z) – 7V ≤ VO ≤ 12V 500 µA 2.0 1.5 35 10 ±5 RS232 Driver (485/232 = Low, ON = DXEN = High) VO Output Voltage Swing Figure 4, RL = 3k, Positive Figure 4, RL = 3k, Negative ● ● IOSD Output Short-Circuit Current VO = 0V ● 5 –5 6.5 – 6.5 ±17 V V ±60 mA Driver Inputs and Control Inputs VIH Input High Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW ● VIL Input Low Voltage DY, DZ, DXEN, RXEN, ON, 485/232, SLEW ● IIN Input Current DY, DZ, DXEN, RXEN, ON, 485/232 SLEW (Note 5) ● ● 2 2 V ±0.1 5 0.8 V ±10 15 µA µA LTC1387 DC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 Receiver (485/232 = High, ON = RXEN = High) VTH Differential Input Threshold Voltage – 7V ≤ VCM ≤ 12V ∆VTH Input Hysteresis VCM = 0V IIN Input Current (A, B) VIN = 12V VIN = – 7V ● ● – 0.8 – 7V ≤ VIN ≤ 12V ● 12 Input Low Threshold Input High Threshold ● ● 0.8 RIN Input Resistance ● – 0.20 0.20 40 V mV 1 24 mA mA kΩ RS232 Receiver (485/232 = Low, ON = RXEN = High) VTH Receiver Input Voltage Threshold ∆VTH Receiver Input Hysteresis RIN Receiver Input Resistance 2.4 0.6 VIN = ±10V 3 5 3.5 4.6 V V V 7 kΩ Receiver Output (ON = RXEN = High) VOH Receiver Output High Voltage IO = – 3mA, VIN = 0V, 485/232 = Low ● VOL Receiver Output Low Voltage IO = 3mA, VIN = 3V, 485/232 = Low ● IOSR Short-Circuit Current 0V ≤ VO ≤ VCC ● IOZR Three-State Output Current RXEN = 0V ● 0.2 7 ±0.1 V 0.4 V 85 mA ±10 µA Power Supply Generator VDD VDD Output Voltage No Load, ON = DXEN = RXEN = High IDD = – 5mA, ON = DXEN = RXEN = High VEE VEE Output Voltage No Load, ON = DXEN = RXEN = High IEE = 5mA, ON = DXEN = RXEN = High 8 7 V V – 7.7 – 7.0 V V Power Supply ICC VCC Supply Current No Load, ON = DXEN = RXEN = High Shutdown, ON = DXEN = RXEN = 0V ● ● 7 5 25 100 mA µA TYP MAX UNITS AC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN RS232 Mode (ON = DXEN = RXEN = High, 485/232 = Low) SR Slew Rate Figure 4, RL = 3k, CL = 15pF Figure 4, RL = 3k, CL = 1000pF ● ● 4 0.22 30 V/µs V/µs 1.9 3.1 µs tT Transition Time Figure 4, RL = 3k, CL = 2500pF ● tPLH Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF ● 0.6 4 µs tPHL Driver Input to Output Figures 4, 10, RL = 3k, CL = 15pF ● 0.6 4 µs tPLH Receiver Input to Output Figures 5, 11 ● 0.3 6 µs tPHL Receiver Input to Output Figures 5, 11 ● 0.4 6 µs RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High) t PLH Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 15 40 70 ns t PHL Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 15 40 70 ns tSKEW Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 5 15 ns t r , tf Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF ● 15 40 ns 3 3 LTC1387 AC ELECTRICAL CHARACTERISTICS TA = 25°C, VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF (Notes 2, 3), unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 Mode (Fast Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = High) tZL Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed ● 50 90 ns tZH tLZ Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed ● 50 90 ns Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed ● 50 90 ns tHZ Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed ● 60 90 ns RS485 Mode (Slow Slew Rate, ON = DXEN = High, 485/232 = High, SLEW = Low) t PLH Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 100 700 1500 ns t PHL Driver Input to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 100 700 1500 ns tSKEW Driver Output to Output Figures 2, 7, RL = 54Ω, CL = 100pF ● 200 750 ns tr, tf Driver Rise or Fall Time Figures 2, 7, RL = 54Ω, CL = 100pF ● 150 300 1500 ns tZL Driver Enable to Output Low Figures 3, 8, CL = 100pF, S1 Closed ● 600 1500 ns tZH Driver Enable to Output High Figures 3, 8, CL = 100pF, S2 Closed ● 600 1500 ns tLZ Driver Disable from Low Figures 3, 8, CL = 15pF, S1 Closed ● 100 200 ns tHZ Driver Disable from High Figures 3, 8, CL = 15pF, S2 Closed ● 100 200 ns RS485 Mode (ON = RXEN = High, 485/232 = High) t PLH Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF ● 20 70 140 ns t PHL Receiver Input to Output Figures 2, 9, RL = 54Ω, CL = 100pF ● 20 70 140 ns tSKEW Differential Receiver Skew, tPLH – tPHL Figures 2, 9, RL = 54Ω, CL = 100pF 10 ns Receiver Output Enable/Disable (ON = High) tZL Receiver Enable to Output Low Figures 6, 12, CL = 15pF, S1 Closed ● 40 90 ns tZH Receiver Enable to Output High Figures 6, 12, CL = 15pF, S2 Closed ● 40 90 ns tLZ Receiver Disable from Low Figures 6, 12, CL = 15pF, S1 Closed ● 40 90 ns tHZ Receiver Disable from High Figures 6, 12, CL = 15pF, S2 Closed ● 40 90 ns The ● denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. 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: All typicals are given at VCC = 5V, C1 = C2 = C3 = C4 = 0.1µF and TA = 25°C. Note 4: Short-circuit current for RS485 driver output low state folds back above VCC. Peak current occurs around VO = 3V. Note 5: SLEW includes an internal pull-up in RS485 mode. U U U PIN FUNCTIONS C1+ (Pin 1): Commutating Capacitor C1 Positive Terminal. Requires an external 0.1µF capacitor between Pins 1 and 2. C1– (Pin 2): Commutating Capacitor C1 Negative Terminal. VDD (Pin 3): Charge Pump Positive Supply Output. Requires an external 0.1µF capacitor to ground. A (Pin 4): Receiver Input A. Inverting input of RS232 receiver A in RS232 mode; inverting RS485 receiver input in RS485 mode. 4 B (Pin 5): Receiver Input B. Inverting input of RS232 receiver B in RS232 mode; noninverting RS485 receiver input in RS485 mode. Y (Pin 6): Driver Output Y. Inverting RS232 driver Y output in RS232 mode; inverting RS485 driver output in RS485 mode. Z (Pin 7): Driver Output Z. Inverting RS232 driver Z output in RS232 mode; noninverting RS485 driver output in RS485 mode. LTC1387 U U U PI FU CTIO S 485/232 (Pin 8): Interface Mode Select Input. A low logic input enables two RS232 drivers and two RS232 receivers. A high input enables the RS485 driver and the RS485 receiver. DXEN (Pin 9): Driver Enable Input. A high logic input enables the drivers and a low logic input disables the drivers. When disabled, all driver outputs are in high impedance GND (Pin 10): Ground. VEE (Pin 11): Charge Pump Negative Supply Output. Requires an external 0.1µF capacitor to ground. RXEN (Pin 12): Receiver Enable Input. A high logic input enables the receivers and a low logic input disables the receivers. When disabled, all receiver outputs are in high impedance. ON (Pin 13): A high logic level at ON input keeps the charge pump active regardless of the state of the DXEN and RXEN inputs. When the charge pump is active, the drivers and receivers can be enabled or disabled without waiting for charge pump stabilization time (typically 100µs with 0.1µF capacitors). A low logic state at the ON, DXEN and RXEN inputs will put the transceiver and charge pump in shutdown mode and reduces ICC to 5µA. Whenever the transceiver is activated from shutdown, the charge pump should be allowed to stabilize before data transmission. When DXEN and RXEN are high and ON is low, the charge pump, drivers and receivers are all active and the driver outputs are internally looped back to the inputs of the receiver. The three control inputs ON, DXEN and RXEN can be configured for one-, two- or three-wire control: onewire mode – all three inputs connected together; two-wire mode – inputs ON and RXEN connected to one wire, DXEN a separate wire; three-wire mode – separate wires to each input. See the Function Tables. DZ/SLEW (Pin 14): Driver Z or Slew Input. In RS232 mode, this pin is the driver Z input. In RS485 mode, this pin controls the slew rate of the RS485 driver. With the SLEW pin high, the RS485 driver runs at maximum (fast) slew rate and can transmit signals up to 5MBd. With the SLEW pin low, the RS485 driver runs with reduced (slow) slew rate to control reflections with improperly terminated cables. In slow mode, the RS485 driver can support data rates up to 150kBd. This SLEW pin has internal 5µA pullup during RS485 mode. DY (Pin 15): Driver Y Input. Input Y in RS232 mode; the differential driver input in RS485 mode. RB (Pin 16): Receiver B Output. Output B in RS232 mode; output is high impedance in RS485 mode. RA (Pin 17): Receiver A Output. Output A in RS232 mode; the differential receiver output in RS485 mode. VCC (Pin 18): Positive Supply. 4.75V ≤ VCC ≤ 5.25V. Requires an external 0.1µF bypass capacitor to ground. C2 – (Pin 19): Commutating Capacitor C2 Negative Terminal. Requires an external 0.1µF capacitor between Pins 19 and 20. C2 + (Pin 20): Commutating Capacitor C2 Positive Terminal. 5 LTC1387 U U FU CTIO TABLES Select Modes SELECT INPUTS ON RXEN DXEN RECEIVER 485/232 RXA DRIVER RXB DXY DXZ CHARGE PUMP LOOPBACK COMMENTS 1 0 0 0 Z Z Z Z ON OFF RS232 Mode, DX and RX Off 1 0 1 0 Z Z ON ON ON OFF RS232 Mode, DXY and DXZ On, RX Off 1 1 0 0 ON ON Z Z ON OFF RS232 Mode, DX Off, RXA and RXB On 1 1 1 0 ON ON ON ON ON OFF RS232 Mode, DXY and DXZ On, RXA and RXB On 0 0 1 0 Z Z ON Z ON OFF RS232 Mode, DXY On, DXZ Off, RX Off 0 1 0 0 Z ON ON Z ON OFF RS232 Mode, DXY On, DXZ Off, RXA Off, RXB On 0 1 1 0 ON ON ON ON ON ON RS232 Loopback Mode, DXY and DXZ On, RXA and RXB On 0 0 0 X Z Z Z Z OFF OFF Shutdown, RS485 RIN 1 0 0 1 Z Z Z Z ON OFF RS485 Mode, DX and RX Off X 0 1 1 Z Z ON ON ON OFF RS485 Mode, DX On, RX Off X 1 0 1 ON Z Z Z ON OFF RS485 Mode, DX Off, RX On 1 1 1 1 ON Z ON ON ON OFF RS485 Mode, DX On, RX On 0 1 1 1 ON Z ON ON ON ON RS485 Loopback Mode, DX On, RX On RS485 Driver Slew Rate RS232 Driver Mode SELECTED INPUTS 485/232 D CONDITIONS OUTPUTS Y, Z DXEN INPUTS 485/232 SLEW OUTPUTS SLEW RATE YES 0 0 No Fault 1 1 1 0 Slow 1 1 Fast 1 X Z YES 0 1 No Fault 0 1 YES 0 X Thermal Fault Z 0 NO 0 X X Z RS485 Driver Mode DXEN INPUTS 485/232 D CONDITIONS 1 1 0 No Fault 0 1 RS232 Receiver Mode OUTPUTS Z Y SELECTED INPUTS 485/232 A, B OUTPUTS RA, RB YES 0 0 1 1 1 1 No Fault 1 0 1 X Thermal Fault Z Z 1 X X Z Z YES 0 1 0 1 YES 0 Inputs Open 1 0 NO 0 X Z RS485 Receiver Mode RXEN 6 INPUTS 485/232 B–A OUTPUTS RA RB 1 1 < – 0.2V 0 Z 1 1 > 0.2V 1 Z 1 1 Inputs Open or Shorted to Ground 1 Z 0 1 X Z Z LTC1387 W BLOCK DIAGRAM RS232 MODE WITHOUT LOOPBACK 1 20 C1 VDD A B Y Z 485/232 DXEN GND 2 19 3 18 4 17 5 16 6 15 7 14 8 13 9 12 10 11 RS485 MODE WITHOUT LOOPBACK 1 20 C2 C1 VCC RA RB DY DZ ON VDD 2 19 3 18 17 4 A 5 B 15 6 Y DXEN GND VCC VDD 14 13 9 12 10 11 RS485 MODE WITH LOOPBACK 20 2 19 3 18 RA 17 16 RB DY Y 8 485/232* VEE 1 C2 C1 7 Z RXEN 16 RS232 MODE WITH LOOPBACK Z SLEW ON RXEN 485/232 DXEN* VEE GND 6 15 7 14 8 13 9 12 10 11 C2 C1 VCC VDD 1 20 2 19 3 18 17 RA 16 RB DY DZ 15 Y Z ON 485/232* RXEN* VEE DXEN* GND 6 7 14 8 13 9 12 10 11 *485/232, DXEN, RXEN = VCC C2 VCC RA RB DY SLEW ON RXEN* VEE LTC1387 • BD TEST CIRCUITS VCC Y R SLEW D VOD CL Y RL R 500Ω DR OUT Z R S1 A CL B 15pF VOC Z 485 = 3V, DXEN = 3V, RXEN = 3V LTC1387 • F02 LTC1387 • F01 Figure 1. RS485 Driver Test Load CL Figure 2. RS485 Driver/Receiver Timing Test Circuit S2 LTC1387 • F03 Figure 3. RS485 Driver Output Enable/Disable Timing Test Load VCC S1 D Y, Z D CL 232 = 0V, DXEN = 3V Figure 4. RS232 Driver Timing Test Circuit Y, Z A, B RECEIVER OUT R RL 15pF 1k CL S2 LTC1387 • F05 LTC1387 • F04 232 = 0V, DXEN = 3V, RXEN = 3V Figure 5. RS232 Receiver Timing Test Circuit LTC1387 • F06 Figure 6. Receiver Output Enable/Disable Timing Test Load 7 LTC1387 U W SWITCHI G WAVEFOR S f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE) f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE) 3V 1.5V D 1.5V 0V tPLH tPHL VO 90% Z–Y 50% 10% –VO VDIFF = V(A) – V(B) 90% 50% 10% 1/2 VO tr tf Y VO Z tSKEW tSKEW LTC1387 • F07 Figure 7. RS485 Driver Propagation Delays f = 1MHz: t r ≤ 10ns: t f ≤ 10ns (FAST SLEW RATE MODE) f = 100kHz: t r ≤ 10ns: t f ≤ 10ns (SLOW SLEW RATE MODE) 3V 1.5V DXEN 1.5V 0V tZL tLZ 5V Y, Z 2.3V OUTPUT NORMALLY LOW VOL tZH OUTPUT NORMALLY HIGH VOH 0.5V tHZ 0.5V 2.3V Z, Y 0V LTC1387 • F08 Figure 8. RS485 Driver Enable and Disable Times V OD2 0V B–A f = 1MHz: t r ≤ 10ns: t f ≤ 10ns INPUT 0V –V OD2 tPLH OUTPUT VOH R tPHL 1.5V 1.5V VOL LTC1387 • F09 Figure 9. RS485 Receiver Propagation Delays 3V 1.5V 1.5V D 0V tPHL tPLH VO Y, Z 0V –VO Figure 10. RS232 Driver Propagation Delays 8 LTC1387 • F10 0V LTC1387 U W SWITCHI G WAVEFOR S V IH 1.7V 1.3V A, B VIL tPHL tPLH VOH 2.4V R LTC1387 • F11 0.8V VOL Figure 11. RS232 Receiver Propagation Delays 3V 1.5V RXEN f = 1MHz: tr ≤ 10ns: tf ≤ 10ns 1.5V 0V tZL tLZ 5V R 1.5V OUTPUT NORMALLY LOW VOL tZH OUTPUT NORMALLY HIGH VOH 0.5V tHZ 0.5V 1.5V R 0V LTC1387 • F12 Figure 12. Receiver Enable and Disable Times U W U UO APPLICATI S I FOR ATIO Basic Theory of Operating The LTC1387 is a single 5V supply, single-port logic reconfigurable RS485/RS232 transceiver with an onboard charge pump. The interface port offers a flexible combination of an RS485 driver and an RS485 receiver or two RS232 drivers and two RS232 receivers. The RS485 transceiver and the RS232 transceivers are designed to share the same I/O pins. A logic input 485/232 controls the selection between RS485 and RS232 transceiver modes. The RS485 transceiver supports both RS485 and RS422 standards, whereas the RS232 transceivers support both RS232 and EIA562 standards. With four additional control inputs: ON, DXEN, RXEN and SLEW, the LTC1387 can easily be reconfigured via software to adapt to various communication needs including a one-signal-line RS232 I/O mode. Four examples of interface port connections are shown in Figures 13 through 16. Both the interface drivers and the receivers feature threestate outputs. Driver outputs are forced into high impedance when the driver is disabled, in the shutdown mode or with the power off. The driver outputs can be forced beyond power supply levels without damage up to ±18V. The receiver inputs can withstand ±25V without damage. The receiver input resistance is typically 24k in RS485 mode, shutdown mode or power off but drops to 5k in RS232 mode. In RS485 mode, the DXEN and RXEN control the threestate outputs of the driver and receiver respectively. The SLEW input is active during RS485 mode and the logic level controls the differential driver slew rate. This pin has an internal 5µA pull-up current source during the RS485 mode. A high logic selects fast differential driver slew rate and a low logic selects slow slew rate. In slow slew mode, the maximum signal bandwidth is reduced, minimizing 9 LTC1387 W U U UO APPLICATI S I FOR ATIO EMI and signal reflection problems. Slow slew rate systems can often use improperly terminated or even unterminated cables with acceptable results. The RS485 differential input receiver features an offset input threshold of – 80mV at 0V common mode voltage. This allows the receiver output to have a known High output state when the inputs are open or shorted. The receiver also features an input hysteresis of 40mV. The charge pump can be kept active regardless of the state of DXEN and RXEN pins by keeping the ON pin High. This improves the receiver response time by removing the 100µs charge pump start-up time. In RS232 mode, the drivers and receivers can be selected from the Function Tables with control inputs ON, RXEN and DXEN. The receivers feature a typical 0.6V input hysteresis. RS232 RS485 A INTERFACE A All the interface driver outputs are fault protected by a current limiting and thermal shutdown circuit. The thermal shutdown circuit disables both the RS232 and RS485 driver outputs when the die temperature reaches 150°C. The thermal shutdown circuit reenables the drivers when the die temperature cools to 135°C. A loopback mode enables internal connections from driver outputs to receiver inputs for self-test. The driver outputs are not isolated from the external loads during loopback. The charge pump generates boosted positive voltage VDD and negative voltage VEE for true RS232 levels from a single 5V VCC supply. The charge pump requires four 0.1µF capacitors. LTC1387 RA RA RS485 B RB B Y DY RB DY DX/RX DZ/SLEW Z ON DZ VCC RXEN DXEN 485/232 CONTROLLER RXEN DXEN MODE RS232 TRANSMIT MODE RS232 RECEIVE MODE RS485 TRANSMIT MODE RS485 RECEIVE MODE SHUTDOWN MODE RXEN = 0 RXEN = 1 RXEN = 0 RXEN = 1 RXEN = 0 DXEN = 1 DXEN = 0 DXEN = 1 DXEN = 0 DXEN = 0 MODE = 0 MODE = 0 MODE = 1 MODE = 1 MODE = X 1387 • F13 Figure 13. Half-Duplex RS232 (1-Channel), Half-Duplex RS485 10 LTC1387 W U U UO APPLICATI S I FOR ATIO LTC1387 RS232 A INTERFACE B RS485 RA A TXD RS232 RA RS485 RXD Y RX RB B RB DY CONTROLLER DY DX DZ/SLEW Z ON DZ VCC RXEN DXEN 485/232 RS232 MODE RS485 TRANSMIT MODE RS485 RECEIVE MODE SHUTDOWN MODE RXEN RXEN = 1 RXEN = 0 RXEN = 1 RXEN = 0 DXEN DXEN = 0 DXEN = 1 DXEN = 0 DXEN = 0 MODE MODE = 0 MODE = 1 MODE = 1 MODE = 0 1387 • F14 Figure 14. Full-Duplex RS232 (1-Channel), Half-Duplex RS485 LTC1387 RS232 A RS485 RA RS485 RS232 RS485 Y RX RB B B INTERFACE Y RA A RXD DY RB CONTROLLER TXD DY RS485 DZ/SLEW Z Z ON DZ RXEN DXEN 485/232 DX VCC RS232 MODE RS485 MODE SHUTDOWN MODE RXEN RXEN = 1 RXEN = 1 RXEN = 0 DXEN DXEN = 1 DXEN = 1 DXEN = 0 MODE MODE = 0 MODE = 1 MODE = X 1387 • F15 Figure 15. Full-Duplex RS232 (1-Channel), Full-Duplex RS485/RS422 LTC1387 RS232 A RS485 RA A RXD RA RS232 B INTERFACE Y RS485 RB B CTS RS232 RS485 Y DY CONTROLLER DY Z RTS RS485 RX2 RB TXD RS232 RX1 DZ/SLEW Z DZ ON RXEN DXEN 485/232 DX1 DX2/SLEW ON RXEN RS232 MODE RS485 MODE SHUTDOWN MODE ON = 1 ON = 1 ON = 0 RXEN = 1 RXEN = 1 RXEN = 0 DXEN DXEN = 1 DXEN = 1 DXEN = 0 MODE MODE = 0 MODE = 1 MODE = X 1387 • F16 Figure 16. Full-Duplex RS232 (2-Channel), Full-Duplex RS485/RS422 with SLEW Control 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LTC1387 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. G Package 20-Lead Plastic SSOP (0.209) (LTC DWG # 05-08-1640) 0.278 – 0.289* (7.07 – 7.33) 20 19 18 17 16 15 14 13 12 11 0.205 – 0.212** (5.20 – 5.38) 0.068 – 0.078 (1.73 – 1.99) 0.301 – 0.311 (7.65 – 7.90) 0° – 8° 0.0256 (0.65) BSC *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0.005 – 0.009 (0.13 – 0.22) 0.022 – 0.037 (0.55 – 0.95) 0.010 – 0.015 (0.25 – 0.38) 0.002 – 0.008 (0.05 – 0.21) 1 2 3 4 5 6 7 8 9 10 G20 SSOP 0595 SW Package 20-Lead Plastic Small Outline (Wide 0.300) (LTC DWG # 05-08-1620) 0.496 – 0.512* (12.598 – 13.005) 0.291 – 0.299** (7.391 – 7.595) 20 0.093 – 0.104 (2.362 – 2.642) 0.010 – 0.029 × 45° (0.254 – 0.737) 18 17 16 15 14 13 12 11 0.037 – 0.045 (0.940 – 1.143) 0° – 8° TYP NOTE 1 0.050 0.004 – 0.012 (1.270) (0.102 – 0.305) TYP 0.014 – 0.019 (0.356 – 0.482) NOTE: TYP 1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS 0.009 – 0.013 (0.229 – 0.330) 19 0.394 – 0.419 (10.007 – 10.643) NOTE 1 0.016 – 0.050 (0.406 – 1.270) 1 2 3 4 5 6 7 8 9 10 S20 (WIDE) 0396 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 Low Power RS485 Interface Transceiver Single 5V Supply, Wide Common Mode Range LT ® 1137A Low Power RS232 Transceiver ±15kV IEC-1000-4-2 ESD Protection, Three Drivers, Five Receivers ® AppleTalk Transceiver AppleTalk /LocalTalk ® Compliant LTC1321/LTC1322/LTC1335 RS232/EIA562/RS485 Transceivers Configurable LTC1323 Single 5V AppleTalk Transceiver AppleTalk /LocalTalk Compliant 10kV ESD LTC1334 Single Supply RS232/RS485 Transceiver Single 5V Supply, Configurable LTC1347 5V Low Power RS232 Transceiver Three Drivers/Five Receivers, Five Receivers Alive in Shutdown LTC1320 AppleTalk and LocalTalk are registered trademarks of Apple Computer Corp. 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1387f LT/GP 0197 7K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1997