LTC1484CS8

LTC1484 Low Power RS485 Transceiver with Receiver Fail-Safe FEATURES s DESCRIPTIO s s s s s s s s s s s No Damage or Latchup to ±15kV ESD (Human Body Model), IEC-1000-4-2 Level 4 Contact (±8kV) and Level 3 (±8kV) Air Gap Specifications Guaranteed High Receiver Output State for Floating, Shorted or Terminated Inputs with No Signal Present Drives Low Cost Residential Telephone Wires Low Power: ICC = 700µA Max with Driver Disabled ICC = 900µA Max for Driver Enable with No Load 20µA Max Quiescent Current in Shutdown Mode Single 5V Supply – 7V to 12V Common Mode Range Permits ± 7V Ground Difference Between Devices on the Data Line Power Up/Down Glitch-Free Driver Outputs Up to 32 Transceivers on the Bus Pin Compatible with the LTC485 Available in 8-Lead MSOP, PDIP and SO Packages The LTC®1484 is a low power RS485 compatible transceiver. In receiver mode, it offers a fail-safe feature which guarantees a high receiver output state when the inputs are left open, shorted together or terminated with no signal present. No external components are required to ensure the high receiver output state. Both driver and receiver feature three-state outputs with separate receiver and driver control pins. The driver outputs maintain high impedance over the entire common mode range when three-stated. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit that forces the driver outputs into a high impedance state. Enhanced ESD protection allows the LTC1484 to withstand ±15kV (human body model), IEC-1000-4-2 level 4 (± 8kV) contact and level 3 (± 8kV) air discharge ESD without latchup or damage. The LTC1484 is fully specified over the commercial and industrial temperature ranges and is available in 8-lead MSOP, PDIP and SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. APPLICATIO S s s s Battery-Powered RS485/RS422 Applications Low Power RS485/RS422 Transceiver Level Translator TYPICAL APPLICATIO RS485 Interface LTC1484 RO1 RE1 DE1 D DI1 GND1 GND2 1484 TA01 LTC1484 VCC1 VCC2 B2 120Ω 120Ω A2 D R RO2 RE2 DE2 DI2 B1 A1 Dl1 R B2 A2 RO2 Dl1 ↑↓ Dl2 = 0 RE1 = RE2 = 0 U Driving a 2000 Foot STP Cable DE1 = VCC DE2 = 0 1484 TA01a U U 1 LTC1484 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (VCC)............................................... 6.5V Control Input Voltages ................. – 0.3V to (VCC + 0.3V) Driver Input Voltage ..................... – 0.3V to (VCC + 0.3V) Driver Output Voltages ................................. – 7V to 10V Receiver Input Voltages (Driver Disabled) .. –12V to 14V Receiver Output Voltage ............... – 0.3V to (VCC + 0.3V) PACKAGE/ORDER INFORMATION ORDER PART NUMBER TOP VIEW RO RE DE DI 1 2 3 4 8 7 6 5 VCC B A GND TOP VIEW RO 1 RE 2 DE 3 D DI 4 R 8 7 6 5 VCC B A GND LTC1484CMS8 MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 200°C/ W MS8 PART MARKING LTDX Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL VOD1 VOD2 PARAMETER Differential Driver Output Voltage (Unloaded) Differential Driver Output Voltage (with Load) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ± 5% (Notes 2 and 3) unless otherwise noted. CONDITIONS IOUT = 0 R = 50Ω (RS422) R = 27Ω (RS485) Figure 1 R = 22Ω, Figure 1 VTST = – 7V to 12V, Figure 2 R = 22Ω, 27Ω or R = 50Ω, Figure 1 VTST = – 7V to 12V, Figure 2 R = 22Ω, 27Ω or R = 50Ω, Figure 1 R = 22Ω, 27Ω or R = 50Ω, Figure 1 DE, DI, RE DE, DI, RE DE, DI, RE DE = 0, VCC = 0 or 5V, VIN = 12V DE = 0, VCC = 0 or 5V, VIN = – 7V – 7V ≤ VCM ≤ 12V, DE = 0 q q q q q q q q q q q q q q VOD3 ∆VOD VOC ∆|VOC| VIH VIL IIN1 IIN2 VTH Differential Driver Output Voltage (with Common Mode) Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Driver Common Mode Output Voltage Change in Magnitude of Driver Common Mode Output Voltage for Complementary Output States Input High Voltage Input Low Voltage Input Current Input Current (A, B) Differential Input Threshold Voltage for Receiver 2 U U W WW U W Junction Temperature .......................................... 125°C Operating Temperature Range LTC1484C ......................................... 0°C ≤ TA ≤ 70°C LTC1484I ...................................... – 40°C ≤ TA ≤ 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER LTC1484CN8 LTC1484CS8 LTC1484IN8 LTC1484IS8 S8 PART MARKING 1484 1484I N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 130°C/ W (N8) TJMAX = 125°C, θJA = 135°C/ W (S8) MIN 2 1.5 1.5 1.5 TYP MAX VCC 5 5 5 0.2 3 0.2 UNITS V V V V V V V V V 2.0 0.8 ±2 1.0 – 0.8 – 0.20 – 0.015 V µA mA mA V LTC1484 The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ± 5% (Notes 2 and 3) unless otherwise noted. SYMBOL ∆VTH VOH VOL IOZR RIN ICC ISHDN IOSD1 IOSD2 IOSR PARAMETER Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Three-State (High Impedance) Output Current at Receiver Receiver Input Resistance Supply Current Supply Current in Shutdown Mode Driver Short-Circuit Current, VOUT = High (Note 4) Driver Short-Circuit Current, VOUT = Low (Note 4) Receiver Short-Circuit Current CONDITIONS VCM = 0V, DE = 0 IOUT = – 4mA, (VA – VB) = 200mV IOUT = 4mA, (VA – VB) = – 200mV VCC = Max, 0.4V ≤ VOUT ≤ 2.4V, DE = 0 –7V ≤ VCM ≤ 12V No Load, Output Enabled (DE = VCC) No Load, Output Disabled (DE = 0) DE = 0, RE = VCC, DI = 0 – 7V ≤ VOUT ≤ 10V – 7V ≤ VOUT ≤ 10V 0V ≤ VOUT ≤ VCC q q q q q q q q q ELECTRICAL CHARACTERISTICS MIN 3.5 TYP ± 30 MAX UNITS mV V 0.4 ±1 12 22 600 400 1 35 35 7 900 700 20 250 250 85 V µA kΩ µA µA µA mA mA mA SWITCHING CHARACTERISTICS SYMBOL tPLH tPHL tSKEW tr, tf tZH tZL tLZ tHZ tPLH tPHL tSKD tZL tZH tLZ tHZ tDZR fMAX tSHDN PARAMETER Driver Input to Output Driver Input to Output Driver Output to Output Driver Rise or Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output Receiver Input to Output |tPLH – tPHL| Differential Receiver Skew Receiver Enable to Output Low Receiver Enable to Output High Receiver Disable from Low Receiver Disable from High Driver Enable to Receiver Valid Maximum Data Rate (Note 5) Time to Shutdown (Note 6) The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. CONDITIONS RDIFF = 54Ω, CL1 = CL2 = 100pF (Figures 4, 6) RDIFF = 54Ω, CL1 = CL2 = 100pF (Figures 4, 6) RDIFF = 54Ω, CL1 = CL2 = 100pF (Figures 4, 6) RDIFF = 54Ω, CL1 = CL2 = 100pF (Figures 4, 6) CL = 100pF (Figures 5, 7) S2 Closed CL = 100pF (Figures 5, 7) S1 Closed CL = 15pF (Figures 5, 7) S1 Closed CL = 15pF (Figures 5, 7) S2 Closed RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 4, 8) RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 4, 8) RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 4, 8) CRL = 15pF (Figures 3, 9) S1 Closed CRL = 15pF (Figures 3, 9) S2 Closed CRL = 15pF (Figures 3, 9) S1 Closed CRL = 15pF (Figures 3, 9) S2 Closed RDIFF = 54Ω, CL1 = CL2 = 100pF (Figures 4, 10) DE = 0, RE↑ q q q q q q q q q q q q q q q q q U MIN 10 10 TYP 28.5 31 2.5 MAX 60 60 10 40 70 100 70 70 200 200 UNITS ns ns ns ns ns ns ns ns ns ns ns 3 15 40 40 40 40 30 30 160 140 20 20 20 20 20 1600 50 50 50 50 3000 ns ns ns ns ns Mbps 4 50 5 300 600 ns 3 LTC1484 SWITCHING CHARACTERISTICS SYMBOL tZH(SHDN) tZL(SHDN) tZH(SHDN) tZL(SHDN) PARAMETER Driver Enable from Shutdown to Output High Driver Enable from Shutdown to Output Low Receiver Enable from Shutdown to Output High Receiver Enable from Shutdown to Output Low The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V ± 5% (Notes 2 and 3) unless otherwise noted. CONDITIONS CL = 100pF (Figures 5, 7) S2 Closed, DI = DE CL = 100pF (Figures 5, 7) S1 Closed, DI = 0 CL = 15pF (Figures 3, 9) S2 Closed, DE = 0 CL = 15pF (Figures 3, 9) S1 Closed, DE = 0 q q q q Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All typicals are given for VCC = 5V and TA = 25°C. Note 3: 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 4: For higher ambient temperatures, the part may enter thermal shutdown during short-circuit conditions. TYPICAL PERFOR A CE CHARACTERISTICS Receiver Output Voltage vs Input Voltage RECEIVER INPUT THRESHOLD VOLTAGE (V) 6 RECEIVER OUTPUT VOLTAGE (V) 5 4 3 2 1 0 –0.2 TA = 25°C VCC = 5V 0 VCC = 5V VTH(HIGH) –0.05 VCM = – 7V –0.10 VCM = 0V –0.15 VCM = 12V RECEIVER INPUT THRESHOLD VOLTAGE (V) VTH(LOW) –0.16 VTH(HIGH) 0 1484 G01 –0.12 –0.08 –0.04 INPUT VOLTAGE (V) 4 UW U MIN TYP 40 40 MAX 100 100 10 10 UNITS ns ns µs µs Note 5: Guaranteed by design. Note 6: Time for ICC to drop to ICC/2 when the receiver is disabled. Receiver Input Threshold Voltage (Output High) vs Temperature 0 Receiver Input Threshold Voltage (Output Low) vs Temperature VCC = 5V VTH(LOW) –0.05 –0.10 –0.15 VCM = 0V –0.20 VCM = – 7V –0.20 VCM = 12V –0.25 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G02 –0.25 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G03 LTC1484 TYPICAL PERFOR A CE CHARACTERISTICS Receiver Input Offset Voltage vs Temperature 0 RECEIVER INPUT OFFSET VOLTAGE (mV) RECEIVER INPUT THRESHOLD VOLTAGE (V) –20 –40 –60 –80 –100 –120 –140 –160 –180 VCC = 5V RECEIVER HYSTERESIS (mV) VCM = – 7V VCM = 0V VCM = 12V –200 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G04 Receiver Output High Voltage vs Output Current 5.0 RECEIVER OUTPUT HIGH VOLTAGE (V) RECEIVER OUTPUT LOW VOLTAGE (V) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 –25 –20 –15 –10 –5 OUTPUT CURRENT (mA) 0 1484 G07 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 5 10 15 20 OUTPUT CURRENT (mA) 25 1484 G08 RECEIVER OUTPUT HIGH VOLTAGE (V) VCC = 4.75V Receiver Output Low Voltage vs Temperature 0.50 RECEIVER OUTPUT LOW VOLTAGE (V) VCM = 12V 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G10 400 INPUT CURRENT (µA) RECEIVER INPUT RESISTANCE (kΩ) 0.45 VCC = 4.75V IOUT = 8mA UW Receiver Hysteresis vs Temperature 100 90 80 70 60 50 40 30 20 10 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G05 Receiver Input Threshold Voltage vs Supply Voltage 0 –0.02 –0.04 –0.06 –0.08 –0.10 –0.12 –0.14 –0.16 –0.18 –0.20 4.5 4.75 5 SUPPLY VOLTAGE (V) 5.25 1484 G06 VCC = 5V TA = 25°C VCM = 0V VTH(HIGH) VTH(HIGH) – VTH(LOW) VCM = – 7V TO 12V VTH(LOW) Receiver Output Low Voltage vs Output Current 1.0 0.9 VCC = 4.75V 4.5 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 Receiver Output High Voltage vs Temperature VCC = 4.75V IOUT = – 8mA 3.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G09 Input Current (A, B) vs Temperature 600 500 26.0 25.5 25.0 24.5 Receiver Input Resistance vs Temperature VCC = 0V OR 5V 300 200 100 0 –100 –200 –300 –400 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G11 VCM = 12V VCM = – 7V VCC = 0V OR 5V 24.0 23.5 23.0 22.5 22.0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G12 VCM = – 7V 5 LTC1484 TYPICAL PERFOR A CE CHARACTERISTICS Receiver Short-Circuit Current vs Temperature 100 RECEIVER SHORT-CIRCUIT CURRENT (mA) RECEIVER PROPAGATION DELAY (ns) 90 80 70 60 50 40 30 20 10 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G13 VCC = 5.25V OUTPUT LOW SHORT TO VCC 140 120 100 80 60 40 20 0 –55 –35 –15 tPHL RECEIVER SKEW (ns) OUTPUT HIGH SHORT TO GROUND Receiver Propagation Delay vs Supply Voltage 200 RECEIVER PROPAGATION DELAY (ns) SHUTDOWN SUPPLY CURRENT (µA) TA = 25°C 180 tPLH 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 SHUTDOWN SUPPLY CURRENT (µA) 160 140 tPHL 120 100 4.5 4.75 5 5.25 SUPPLY VOLTAGE (V) Supply Current vs Temperature 1000 900 800 SUPPLY CURRENT (µA) 700 600 500 400 300 200 100 0 –55 –30 –5 20 45 70 95 120 145 170 TEMPERATURE (°C) 1484 G19 LOGIC INPUT THRESHOLD VOLTAGE (V) VCC = 5V THERMAL SHUTDOWN WITH DRIVER ENABLED SUPPLY CURRENT (µA) DRIVER ENABLED NO LOAD DRIVER DISABLED 6 UW 5.5 1484 G16 Receiver Propagation Delay vs Temperature 200 180 160 VCC = 5V tPLH 25 20 15 10 5 30 Receiver Skew vs Temperature VCC = 5V 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G14 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G15 Shutdown Supply Current vs Temperature 1.00 VCC = 5V DE = DI = 0 RE = 5V 0.95 0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 Shutdown Supply Current vs Supply Voltage TA = 25°C 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G17 0.50 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 SUPPLY VOLTAGE (V) 1484 G18 Supply Current vs Supply Voltage 700 TA = 25°C 600 500 400 300 200 100 0 4.5 4.6 4.7 4.8 4.9 5 5.1 5.2 5.3 5.4 5.5 SUPPLY VOLTAGE (V) 1484 G20 Logic Input Threshold vs Temperature 2.00 1.95 1.90 1.85 1.80 1.75 1.70 1.65 1.60 1.55 1.50 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G21 DRIVER ENABLED NO LOAD VCC = 5.25V VCC = 5V DRIVER DISABLED VCC = 4.75V LTC1484 TYPICAL PERFOR A CE CHARACTERISTICS Driver Differential Output Voltage vs Temperature DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) 3.0 RL = 44Ω 2.5 2.0 1.5 1.0 0.5 ∆VOD, VCC = 4.5V TO 5.25V 0 –0.5 –55 –35 –15 3.0 2.5 2.0 1.5 1.0 0.5 ∆VOD, VCC = 4.5V TO 5.25V 0 –0.5 –55 –35 –15 VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V RL = 54Ω DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G22 Driver Common Mode Output Voltage vs Temperature 3.0 DRIVER COMMON MODE VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 ∆VOC, VCC = 4.5V TO 5.25V 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G25 RL = 44Ω DRIVER COMMON MODE VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 ∆VOC, VCC = 4.5V TO 5.25V 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G26 DRIVER COMMON MODE VOLTAGE (V) VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V Driver Differential Output Voltage vs Temperature DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) 3.5 SEE FIGURE 2 3.0 2.5 2.0 1.5 1.0 0.5 0 –0.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G28 VCM = – 7V VOD3 DI HIGH DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V ∆VOD3 FOR VCC = 4.5V TO 5.25V UW Driver Differential Output Voltage vs Temperature 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Driver Differential Output Voltage vs Temperature RL = 100Ω VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V ∆VOD, VCC = 4.5V TO 5.25V 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G23 –0.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G24 Driver Common Mode Output Voltage vs Temperature 3.0 RL = 54Ω 3.0 2.5 2.0 1.5 1.0 0.5 Driver Common Mode Output Voltage vs Temperature RL = 100Ω VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V VCC = 5.25V VCC = 5V VCC = 4.75V VCC = 4.5V ∆VOC, VCC = 4.5V TO 5.25V 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G27 Driver Differential Output Voltage vs Temperature 3.0 2.5 2.0 1.5 1.0 0.5 ∆VOD3 FOR VCC = 4.5V TO 5.25V 0 –0.5 –55 –35 –15 VCC = 5.25V 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Driver Differential Output Voltage vs Output Current VCC = 5V TA = 25°C VCC = 5V VCC = 4.75V VCC = 4.5V VCM = 12V VOD3 DI HIGH SEE FIGURE 2 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G29 0 10 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT (mA) 1484 G30 7 LTC1484 TYPICAL PERFOR A CE CHARACTERISTICS Driver Output High Voltage vs Output Current 5.0 DRIVER OUTPUT HIGH VOLTAGE (V) DRIVER OUTPUT LOW VOLTAGE (V) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 –100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0 OUTPUT CURRENT (mA) 1484 G31 2.5 2.0 1.5 1.0 0.5 0 DRIVER PROPAGATION DELAY (ns) VCC = 4.75V Driver Short-Circuit Current vs Temperature 250 DRIVER SHORT-CIRCUIT CURRENT (mA) VCC = 5.25V 200 DRIVER SKEW (ns) DRIVER OUTPUT HIGH SHORT TO –7V 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G34 DRIVER PROPAGATION DELAY (ns) 150 100 DRIVER OUTPUT LOW SHORT TO 10V 50 PIN FUNCTIONS RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low) and the part is not in shutdown, RO is high if (A – B) > VTH(MAX) and low if (A – B) < VTH(MIN). RO is also high if the receiver inputs are open or shorted together, with or without a termination resistor. RE (Pin 2): Receiver Output Enabled. A high on this pin three-states the receiver output (RO) and a low enables it. DE (Pin 3): Driver Enable Input. DE = high enables the output of the driver with the driver outputs determined by the DI pin. DE = low forces the driver outputs into a high impedance state. The LTC1484 enters shutdown when both receiver and driver outputs are disabled (RE is high and DE is low). DI (Pin 4): Driver Input. When the driver outputs are enabled (DE high), DI high takes the A output high and the B output low. DI low takes the A output low and the B output high. GND (Pin 5): Ground. 8 UW Driver Output Low Voltage vs Output Current 3.0 VCC = 4.75V 50 45 40 35 30 25 20 15 10 5 0 10 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT (mA) 1484 G32 Driver Propagation Delay vs Temperature VCC = 5V tPHL tPLH 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G33 Driver Skew vs Temperature 40 35 30 25 20 15 10 5 0 Driver Propagation Delay vs Supply Voltage TA = 25°C tPHL tPLH 0 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1484 G35 4.5 4.75 5 5.25 SUPPLY VOLTAGE (V) 5.5 1484 G36 U U U LTC1484 PIN FUNCTIONS A (Pin 6): Driver Output/Receiver Input. The input resistance is typically 22k when the driver is disabled (DE = 0). When the driver is enabled, the A output follows the logic level at the DI pin. B (Pin 7): Driver Output/Receiver Input. The input resistance is typically 22k when the driver is disabled (DE = 0). When the driver is enabled, the B output is inverted from the logic level at the DI pin. VCC (Pin 8): Positive Supply. 4.75V ≤ VCC ≤ 5.25V. A 0.1µF bypass capacitor is recommended. FU CTIO TABLES Driver INPUTS RE X X O 1 DE 1 1 0 0 DI 1 0 X X B 0 1 Z Z* OUTPUTS A 1 0 Z Z* RE 0 0 0 0 1 DE 0 0 0 0 X Note: Z = high impedance, X = don’t care *Shutdown mode for LTC1484 TEST CIRCUITS A R VOD1 VOD2 R B 1484 F01 VOC B Figure 1 DE A DI B RDIFF CL2 RE 1484 F04 U U U U U Receiver INPUTS A–B ≥ VTH(MAX) ≤ VTH(MIN) Inputs Open Inputs Shorted X OUTPUTS RO 1 0 1 1 Z† † Shutdown mode for LTC1484 if DE = 0. Table valid with or without termination resistors. A 375Ω OUTPUT UNDER TEST S1 1k VCC CRL 1k S2 1484 F03 VOD3 60Ω 375Ω –7V TO 12V 1484 F02 Figure 2 Figure 3 CL1 A RO B 15pF OUTPUT UNDER TEST 500Ω CL S1 VCC S2 1484 F05 Figure 4 Figure 5 9 LTC1484 SWITCHI G TI E WAVEFOR S 3V DI 0V t PLH VO –VO B VO A 1/2 VO NOTE: DE = 1 tSKEW t SKEW 1484 F06 1.5V 10% tr 90% 50% Figure 6. Driver Propagation Delays 3V DE 0V 5V A, B VOL VOH A, B 0V t ZH(SHDN), t ZH 2.3V t ZL(SHDN), t ZL 2.3V 1.5V NOTE: A, B ARE THREE-STATED WHEN DE = 0, 1kΩ PULL-UP OR 1kΩ PULL-DOWN Figure 7. Driver Enable and Disable Timing VOD2 A–B – VOD2 5V RO VOL 0V t PHL 1.5V NOTE: tSKD = |tPHL – tPLH|, RE = 0 Figure 8. Receiver Propagation Delays RE 1.5V t ZL(SHDN), tZL 1.5V 0V 5V 5V RO RO 0V 1.5V t ZH(SHDN), tZH NOTE: DE = 0, RO IS THREE-STATED IN SHUTDOWN, 1kΩ PULL-UP FOR NORMALLY LOW OUTPUT, 1kΩ PULL-DOWN FOR NORMALLY HIGH OUTPUT Figure 9. Receiver Enable and Shutdown Timing 10 W W U f = 1MHz, tr ≤ 10ns, tf ≤ 10ns t PHL VO = V(A) – V(B) 50% tf 1.5V 90% 10% f = 1MHz, tr ≤ 10ns, tf ≤ 10ns t LZ OUTPUT NORMALLY LOW 1.5V 0.5V 0.5V t HZ 1484 F07 OUTPUT NORMALLY HIGH INPUT f = 1MHz, tr ≤ 10ns, tf ≤ 10ns OUTPUT t PLH 0V 1.5V 1484 F08 f = 1MHz, tr ≤ 10ns, tf ≤ 10ns t LZ OUTPUT NORMALLY LOW 1.5V 0.5V 0.5V t HZ 1484 F09 OUTPUT NORMALLY HIGH LTC1484 SWITCHI G TI E WAVEFOR S 3V DE 0V t DZR V(A) – V(B) OUTPUT NORMALLY LOW 1.5V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns RO 1.5V NOTE: DI = 0, RE = 0, A AND B ARE THREE-STATED WHEN DE = 0 Figure 10. Driver Enable to Receiver Valid Timing APPLICATIONS INFORMATION Low Power Operation The LTC1484 has a quiescent current of 900µA max when the driver is enabled. With the driver in three-state, the supply current drops to 700µA max. The difference in these supply currents is due to the additional current drawn by the internal 22k receiver input resistors when the driver is enabled. Under normal operating conditions, the additional current is overshadowed by the 50mA current drawn by the external termination resistor. Receiver Open-Circuit Fail-Safe Some encoding schemes require that the output of the receiver maintain a known state (usually a logic 1) when data transmission ends and all drivers on the line are forced into three-state. Earlier RS485 receivers with a weak pull-up at the A input will give a high output only when the inputs are floated. When terminated or shorted together, the weak pull-up is easily defeated causing the receiver output to go low. External components are needed if a high receiver output is mandatory. The receiver of the LTC1484 has a fail-safe feature which guarantees the output to be in a logic 1 when the receiver inputs are left open or shorted together, regardless of whether the termination resistor is present or not. In encoding schemes where the required known state is a low, external components are needed for the LTC1484 and other RS485 parts. Fail-safe is achieved by making the receiver trip points fall within the VTH(MIN) to VTH(MAX) range. When any of the listed receiver input conditions exist, the receiver inputs are effectively at 0V and the receiver output goes high. The receiver fail-safe mechanism is designed to reject fast common mode steps (– 7V to 12V in 10ns) switching at 100kHz typ. This is achieved through an internal carrier detect circuit similar to the LTC1482. This circuit has builtin delays to prevent glitches while the input swings between ± VTH(MAX) levels. When all the drivers connected to the receiver inputs are three-stated, the internal carrier detect signal goes low to indicate that no differential signal is present. When any driver is taken out of three-state, the carrier detect signal takes 1.6µs typ (see tDZR) to detect the enabled driver. During this interval, the transceiver output (RO) is forced to the fail-safe high state. After 1.6µs, the receiver will respond normally to changes in driver output. If the part is taken out of shutdown mode with the receiver inputs floating, the receiver output takes about 10µs to leave three-state (see tZL(SHDN)). If the receiver inputs are actively driven to a high state, the outputs go high after about 5.5µs. W U W U W U U OUTPUT NORMALLY HIGH 1484 F10 11 LTC1484 APPLICATIONS INFORMATION Shutdown Mode The receiver output (RO) and the driver outputs (A, B) can be three-stated by taking the RE and DE pins high and low respectively. Taking RE high and DE low at the same time puts the LTC1484 into shutdown mode and ICC drops to 20µA max. In some applications (see CDMA), the A and B lines are pulled to VCC or GND through external resistors to force the line to a high or low state when all connected drivers are disabled. In shutdown, the supply current will be higher than 20µA due to the additional current drawn through the external pull-up and the 22k input resistance of the LTC1484. ESD Protection The ESD performance of the LTC1484 A and B pins is characterized to meet ±15kV using the Human Body Model (100pF, 1.5kΩ), IEC-1000-4-2 level (± 8kV) contact mode and IEC-1000-4-2 level 3 (± 8kV) air discharge mode. This means that external voltage suppressors are not required in many applications when compared with parts that are only protected to ± 2kV. Pins other than the A and B pins are protected to ± 4.5kV typical per the Human Body Model. When powered up, the LTC1484 does not latch up or sustain damage when the A and B pins are tested using any of the three conditions listed. The data during the ESD event may be corrupted, but after the event the LTC1484 continues to operate normally. The additional ESD protection at the A and B pins is important in applications where these pins are exposed to the external world via connections to sockets. Fault Protection When shorted to –7V or 10V at room temperature, the short-circuit current in the driver pins is limited by internal resistance or protection circuitry to 250mA. Over the industrial temperature range, the absolute maximum positive voltage at any driver pin should be limited to 10V to avoid damage to the driver pins. At higher ambient temperatures, the rise in die temperature due to the short-circuit current may trip the thermal shutdown circuit. When the driver is disabled, the receiver inputs can withstand the entire – 7V to 12V RS485 common mode range without damage. The LTC1484 includes a thermal shutdown circuit which protects the part against prolonged shorts at the driver outputs. If a driver output is shorted to another output or to VCC, the current will be limited to 250mA. If the die temperature rises above 150°C, the thermal shutdown circuit three-states the driver outputs to open the current path. When the die cools down to about 130°C, the driver outputs are taken out of three-state. If the short persists, the part will heat again and the cycle will repeat. This thermal oscillation occurs at about 10Hz and protects the part from excessive power dissipation. The average fault current drops as the driver cycles between active and three-state. When the short is removed, the part will return to normal operation. Carrier Detect Multiple Access (CDMA) Application In normal half-duplex RS485 systems, only one node can transmit at a time. If an idle node suddenly needs to gain access to the twisted pair while other communications are in progress, it must wait its turn. This delay is unacceptable in safety-related applications. A scheme known as Carrier Detect Multiple Access (CDMA) solves this problem by allowing any node to interrupt on-going communications. Figure 11 shows four nodes in a typical CDMA communications system. In the absence of any active drivers, bias resistors (1.2k) force a “1” across the twisted pair. All drivers in the system are connected so that when enabled, they transmit a “0”. This is accomplished by tying DI low and using DE as the driver data input. A “1” is transmitted by disabling the driver’s “0” output and allowing the bias resistors to reestablish a “1” on the twisted pair. Control over communications is achieved by asserting a “0” during the time an active transmitter is sending a “1”. Any node that is transmitting data watches its own 12 U W U U LTC1484 APPLICATIONS INFORMATION 1k RO4 DE4 123 5V 1.2k 5V 8 67 120Ω 8 R 1 1k 23 67 5 5 76 8 R 4 D 5 5 76 120Ω D 4 DE2 RO2 321 R 8 5V 5V 1.2k 1k 1.2k 5V D 4 RO1 DE1 Figure 11. Transmit “0” CDMA Application receiver output and expects to see perfect agreement between the two data streams. (Note that the driver inverts the data, so the transmitted and received data streams are actually opposites.) If the simultaneously transmitted and received data streams differ (usually detected by comparing RO and DE with an XOR), it signals the presence of a second, active driver. The first driver falls silent, and the second driver seizes control. If the LTC1484 is connected as shown in Figure 11, the overhead of XORing the transmitted and received data in hardware or software is eliminated. DE and RE are connected together so the receiver is disabled and its output three-stated whenever a “0” is transmitted. A 1k pull-up ensures a “1” at the receiver output during this condition. The receiver is enabled when the driver is disabled. During this interval the receiver output should also be “1”. Thus, under normal operation the receiver output is always “1”. If a “0” is detected, it indicates the presence of a second active driver attempting to seize control of communications. The maximum frequency at which the system in Figure 11 can operate is determined by the cable capacitance, the values of the pull-up and pull-down resistors and receiver propagation delay. The external resistors take a longer time to pull the line to a “1” state due to higher source resistance compared to an active driver, thereby affecting the duty cycle of the receiver output at the far end of the line. U W U U 5V 1.2k D 4 R 321 1484 F11 DE3 RO3 1k Figure 12a shows a 100kHz DE1 waveform for an LTC1484 driving a 1000-foot shielded twisted-pair (STP) cable and the A2, B2 and RO2 waveforms of a receiving LTC1484 at the far end of the cable. The propagation delay between DE1 of the driver and RO2 at the far end of the line is 1.8µs at the rising edge and 3.7µs at the falling edge of DE1. The DE1 B2 A2 RO2 (a) 1484 F12a DE1 B2 A2 RO2 (b) 1484 F12b Figure 12. LTC1484 Driving a 1000 Foot STP Cable 13 LTC1484 APPLICATIONS INFORMATION longer delay for the falling edge is due to the larger voltage range the line must swing (typically > 2V compared to 370mV) before the receiver trips high again. The difference in delay affects the duty cycle of the received data and depends on cable capacitance. For a 1-foot STP cable, the delays drop to 0.13µs and 0.4µs. Using smaller valued pull-up and pull-down resistors to equalize the positive and negative voltage swings needed to trip the receivers will reduce the difference in delay and increase the maximum data rate. With 220Ω resistors, both rising and falling edge delays are 2.2µs when driving a 1000-foot STP cable as shown in Figure 12b. The fail-safe feature of the LTC1484 receiver allows a CDMA system to function without the A and B pull-up and pull-down resistors. However, if the resistors are left out, noise margin will be reduced to as low as 15mV and propagation delays will increase significantly. Operation in this mode is not recommended. Since DE and RE are tied together, the part never shuts down. The receiver inputs are never floating (due to the external bias resistors) so that the tDZR timing does not apply to this application. The whole system can be changed to actively transmit only a “1” by swapping the pull-up and pull-down resistors in Figure 11, shorting DI to VCC and connecting the 1k resistor as a pull-down. In this configuration the driver is noninverting and the receiver output RO truly follows DE. PACKAGE DESCRIPTION Dimensions in inches (millimeters), unless otherwise noted. 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.021 ± 0.006 (0.53 ± 0.015) 0° – 6° TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) BSC * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE 14 U U W U U MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 0.034 ± 0.004 (0.86 ± 0.102) 8 76 5 0.006 ± 0.004 (0.15 ± 0.102) 0.193 ± 0.006 (4.90 ± 0.15) 0.118 ± 0.004** (3.00 ± 0.102) MSOP (MS8) 1098 1 23 4 LTC1484 PACKAGE DESCRIPTION 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 ) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 0.014 – 0.019 (0.355 – 0.483) TYP *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 0.016 – 0.050 (0.406 – 1.270) 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. U Dimensions in inches (millimeters), unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.400* (10.160) MAX 8 7 6 5 0.255 ± 0.015* (6.477 ± 0.381) 1 2 3 4 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) N8 1098 0.100 (2.54) BSC S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) 1 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC SO8 1298 15 LTC1484 TYPICAL APPLICATIO RELATED PARTS PART NUMBER LTC485 LTC1480 LTC1481 LTC1482 LTC1483 LTC1485 LTC1487 LTC1535 LTC1685 LTC1690 LT1785 DESCRIPTION 5V Low Power RS485 Interface Transceiver 3.3V Ultralow Power RS485 Transceiver with Shutdown 5V Ultralow Power RS485 Transceiver with Shutdown 5V Low Power RS485 Transceiver with Carrier Detect Output 5V Ultralow Power RS485 Low EMI Transceiver with Shutdown 5V RS485 Transceiver 5V Ultralow Power RS485 with Low EMI, Shutdown and High Input Impedance Isolated RS485 Transceiver 52Mbps RS485 Transceiver 5V Differential Driver and Receiver Pair with Fail-Safe Receiver Output ± 60V Fault Protected RS485 Transceiver COMMENTS Low Power Lower Supply Voltage Lowest Power Low Power, High Output State When Inputs are Open, Shorted or Terminated, ±15kV ESD Protection Low EMI, Lowest Power High Speed, 10Mbps, ± 15kV ESD Protection Highest Input Impedance, Low EMI, Lowest Power 2500VRMS Isolation Propagation Delay Skew 500ps (Typ) Low Power, ± 15kV ESD Protection ±15kV ESD Protection, Industry Standard Pinout 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com U Fail-Safe “0” Application (Idle State = Logic “0”) 5V RO RE DE DI I2 I1 RO RE DE DI D GND 1484 TA02 LTC1484 R VCC B A “A” “B” 1484f LT/TP 0400 4K • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 1998