LTC1480 3.3V Ultra-Low Power RS485 Transceiver U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ True RS485 from a Single 3.3V Supply Low Power: ICC = 500µA Max with Driver Disabled ICC = 600µA Max with Driver Enabled, No Load 1µA Quiescent in Shutdown Mode ESD Protection to ±10kV on Receiver Inputs and Driver Outputs –7V to 12V Common-Mode Range Permits ±7V Ground Difference Between Devices on the Data Line Thermal Shutdown Protection Power Up/Down Glitch-Free Driver Outputs Permit Live Insertion or Removal of Transceiver Driver Maintains High Impedance in Three-State or with the Power Off Up to 32 Transceivers on the Bus 50ns Typical Driver Propagation Delays with 10ns Skew Pin Compatible with the LTC485 UO APPLICATI ■ ■ ■ S The LTC®1480 is an ultra-low power differential line transceiver which provides full RS485 compatibility while operating from a single 3.3V supply. It is designed for data transmission standard RS485 applications with extended common-mode range (12V to –7V). It also meets the requirements of RS422 and features high speed operation up to 2.5Mb/s. The CMOS design offers significant power savings without sacrificing ruggedness against overload or ESD damage. Typical quiescent current is only 300µA while operating and 1µA in shutdown. The driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common-mode range. Excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. The receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. I/O pins are protected against multiple ESD strikes of up to ±10kV. The LTC1480 is fully specified over the commercial and extended industrial temperature range. The LTC1480 is available in 8-pin SO and DIP packages. Battery-Powered RS485/RS422 Applications Low Power RS485/RS422 Transceiver Level Translator , LTC and LT are registered trademarks of Linear Technology Corporation. UO TYPICAL APPLICATI Driver Differential Output Voltage vs Output Current 3.3V RS485 Network 3.3V 3.3V LTC1480 RE DE D1 R 8 7 2 SHIELD B 120Ω 6 3 4 D 5 8 SHIELD B 7 2 A 6 3 120Ω A 5 3.3V B A 8 7 6 D 5 DE D1 2.5 2.0 1.5 1.0 0.5 LTC1480 R 4 RE VCC = 3.3V TA = 25°C 3.0 1 RO R OUTPUT VOLTAGE (V) RO 1 3.5 LTC1480 D 0 1 RO 2 RE 3 4 DE D1 0 LTC1480 • TA01 10 20 30 40 50 60 70 OUTPUT CURRENT (mA) 80 90 LTC1480 • TA02 1 LTC1480 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) ................................................ 7V Control Input Voltage ..................... – 0.3V to VCC + 0.3V Driver Input Voltage ....................... – 0.3V to VCC + 0.3V Driver Output Voltage ........................................... ±14V Receiver Input Voltage .......................................... ±14V Receiver Output Voltage ................ – 0.3V to VCC + 0.3V Operating Temperature Range LTC1480C........................................ 0°C ≤ TA ≤ 70°C LTC1480I .................................... – 40°C ≤ TA ≤ 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ELECTRICAL CHARACTERISTICS TOP VIEW RO 1 R RE 2 DE 3 DI 4 D N8 PACKAGE 8-LEAD PDIP 8 VCC 7 B 6 A 5 GND S8 PACKAGE 8-LEAD PLASTIC SO ORDER PART NUMBER LTC1480CN8 LTC1480IN8 LTC1480CS8 LTC1480IS8 S8 PART MARKING TJMAX = 125°C, θJA = 130°C/ W (N8) TJMAX = 125°C, θJA = 150°C/ W (S8) 1480 1480I Consult factory for Military grade parts. VCC = 3.3V (Notes 2, 3) SYMBOL PARAMETER CONDITIONS VOD1 Differential Driver Output Voltage (Unloaded) IO = 0V ● MAX UNITS 3.3 V VOD2 Differential Driver Output Voltage (with Load) R = 27Ω (RS485), Figure 1 R = 50Ω (RS422) ● ● 3.3 V V ∆VOD Change in Magnitude of Driver Differential Output Voltage for Complementary Output States R = 27Ω or R = 50Ω, Figure 1 ● 0.2 V VOC Driver Common-Mode Output Voltage R = 27Ω or R = 50Ω, Figure 1 ● 2 V ∆VOC Change in Magnitude of Driver Common-Mode Output Voltage for Complementary Output States R = 27Ω or R = 50Ω, Figure 1 ● 0.2 V VIH Input HIGH Voltage DE, DI, RE ● VIL Input LOW Voltage DE, DI, RE ● 0.8 V IIN1 Input Current DE, DI, RE ● ±2 µA IIN2 Input Current (A, B) DE = 0, VCC = 0V or 3.6V, VIN = 12V DE = 0, VCC = 0V or 3.6V, VIN = – 7V ● ● 1.0 – 0.8 mA mA VTH Differential Input Threshold Voltage for Receiver – 7V ≤ VCM ≤ 12V ● 0.2 V ∆VTH Receiver Input Hysteresis VCM = 0V VOH Receiver Output HIGH Voltage IO = – 4mA, VID = 200mV ● VOL Receiver Output LOW Voltage IO = 4mA, VID = – 200mV ● 0.4 V IOZR Three-State (High Impedance) Output Current at Receiver VCC = Max, 0.4V ≤ VO ≤ 2.4V ● ±1 µA RIN Receiver Input Resistance – 7V ≤ VCM ≤ 12V ● ICC Supply Current No Load, Output Enabled No Load, Output Disabled ● ● ISHDN Supply Current in Shutdown Mode DE = 0, RE = VCC IOSD1 Driver Short-Circuit Current, VOUT = HIGH – 7V ≤ VO ≤ 12V ● IOSD2 Driver Short-Circuit Current, VOUT = LOW – 7V ≤ VO ≤ 12V IOSR Receiver Short-Circuit Current 0V ≤ VO ≤ VCC 2 MIN TYP 1.5 2.0 2 V – 0.2 70 mV 2 V 12 kΩ 400 300 600 500 µA µA 1 10 µA 35 250 mA ● 35 250 mA ● 7 85 mA LTC1480 U SWITCHI G CHARACTERISTICS VCC = 3.3V (Notes 2, 3) SYMBOL PARAMETER CONDITIONS MIN TYP MAX tPLH Driver Input to Output RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 3 and 5) tPHL UNITS ● 25 50 80 Driver Input to Output ● 25 50 80 tSKEW Driver Output to Output ● 10 20 tR, tF Driver Rise or Fall Time ● 5 15 40 tZH Driver Enable to Output HIGH CL = 100pF (Figures 4, 6), S2 Closed ● 70 120 ns tZL Driver Enable to Output LOW CL = 100pF (Figures 4, 6), S1 Closed ● 70 120 ns tLZ Driver Disable Time from LOW CL = 15pF (Figures 4, 6), S1 Closed ● 70 120 ns tHZ Driver Disable Time from HIGH CL = 15pF (Figures 4, 6), S2 Closed ● 70 120 ns tPLH Receiver Input to Output RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figure 3, 7) ● 30 140 200 ns tPHL Receiver Input to Output ● 30 140 200 ns tSKD tPLH – tPHL Differential Receiver Skew tZL Receiver Enable to Output LOW tZH tLZ ns 13 ns CRL = 15pF (Figures 2, 8), S1 Closed ● 50 80 ns Receiver Enable to Output HIGH CRL = 15pF (Figures 2, 8), S2 Closed ● 50 80 ns Receiver Disable from LOW CRL = 15pF (Figures 2, 8), S1 Closed ● 50 80 ns tHZ Receiver Disable from HIGH CRL = 15pF (Figures 2, 8), S2 Closed ● 50 80 ns fMAX Maximum Data Rate ● 2.5 tSHDN Time to Shutdown DE = 0, RE = ● 50 200 600 ns tZH(SHDN) Driver Enable from Shutdown to Output HIGH CL = 100pF (Figures 4, 6), S2 Closed ● 70 120 ns tZL(SHDN) Driver Enable from Shutdown to Output LOW CL = 100pF (Figures 4, 6), S1 Closed ● 70 120 ns tZH(SHDN) Receiver Enable from Shutdown to Output HIGH CL = 15pF (Figures 2, 8), S2 Closed ● 4500 ns tZL(SHDN) Receiver Enable from Shutdown to Output LOW CL = 15pF (Figures 2, 8), S1 Closed ● 4500 ns The ● denotes specifications which apply over the full operating temperature range. Note 1: Absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed. Mbits/s Note 2: All currents into device pins are positive; all currents out ot device pins are negative. All voltages are referenced to device ground unless otherwise specified. Note 3: All typicals are given for VCC = 3.3V and TA = 25°C. U W TYPICAL PERFORMANCE CHARACTERISTICS Driver Output Low/High Voltage vs Output Current Supply Current vs Temperature 350 325 300 DRIVER DISABLED 275 250 VCC = 3.3V TA = 25°C 100 50 0 – 50 0 2.0 1.9 RL = 54Ω 1.8 1.7 –100 1.6 –150 1.5 –40 –20 VCC = 3.3V VCC = 3.3V 200 –50 –25 RL = 100Ω 2.1 DIFFERENTIAL VOLTAGE (V) THERMAL SHUTDOWN WITH DRIVER ENABLED 375 OUTPUT CURRENT (mA) 400 SUPPLY CURRENT (µA) 2.2 150 425 225 Driver Differential Output Voltage vs Temperature 25 50 75 100 125 150 175 TEMPERATURE (°C) LT1480 • TPC01 0 0.5 2.5 1.0 1.5 2.0 OUTPUT VOLTAGE (V) 3.0 3.5 LT1480 • TPC02 40 20 60 0 TEMPERATURE (°C) 80 100 LTC1480 • TPC03 3 LTC1480 U W TYPICAL PERFORMANCE CHARACTERISTICS Receiver Output Low Voltage vs Output Current Driver Skew vs Temperature 25 7.0 20 OUTPUT CURRENT (mA) 6.0 TIME (ns) – 16 VCC = 3.3V TA = 25°C VCC = 3.3V 5.5 5.0 4.5 4.0 – 14 OUTPUT CURRENT (mA) 6.5 Receiver Output High Voltage vs Output Current 15 10 – 12 – 10 5 3.5 –8 –6 –4 –2 3.0 – 40 – 20 0 0 40 60 20 TEMPERATURE (°C) 80 100 0 3.30 3.05 2.80 2.55 2.30 2.05 1.80 1.55 1.30 OUTPUT VOLTAGE (V) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 OUTPUT VOLTAGE (V) LTC1480 • TPC05 LT1480 • TPC04 Receiver tPLH – tPHL vs Temperature LT1480 • TPC06 Receiver Output Low Voltage vs Temperature 12 Receiver Output High Voltage vs Temperature 3.0 0.6 10 OUTPUT VOLTAGE (V) 0.5 8 6 4 VCC = 3.3V 1 = 8mA 2.8 OUTPUT VOLTAGE (V) VCC = 3.3V TIME (ns) VCC = 3.3V TA = 25°C 0.4 0.3 0.2 0 –40 –20 40 20 60 0 TEMPERATURE (°C) 80 100 0 –40 –20 2.6 2.4 2.2 0.1 2 VCC = 3.3V 1 = 8mA 40 20 60 0 TEMPERATURE (°C) LT1480 • TPC07 80 100 2.0 – 40 – 20 40 20 0 60 TEMPERATURE (°C) LTC1480 • TPC08 80 100 LTC1480 • TPC09 U U U PIN FUNCTIONS RO (Pin 1): Receiver Output. If the receiver output is enabled (RE LOW) and A > B by 200mV, then RO will be HIGH. If A < B by 200mV, then RO will be LOW. RE (Pin 2): Receiver Output Enable. A LOW enables the receiver output, RO. A HIGH input forces the receiver output into a high impedance state. DE (Pin 3): Driver Outputs Enable. A HIGH on DE enables the driver output. A, B and the chip will function as a line driver. A low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. If RE is high and DE is LOW, the part will enter a low power (1µA) shutdown state. If RE is low and DE is 4 high, the driver outputs will be fed back to the receiver and the receive output will correspond to the driver input. DI (Pin 4): Driver Input. If the driver outputs are enabled (DE HIGH) then a low on DI forces the outputs A LOW and B HIGH. A HIGH on DI with the driver outputs enabled will force A HIGH and B LOW. GND (Pin 5): Ground. A (Pin 6): Driver Output/Receiver Input. B (Pin 7): Driver Output/Receiver Input. VCC (Pin 8): Positive Supply. 3.0V < VCC < 3.6V. LTC1480 U U FU CTIO TABLES LTC1480 Receiving LTC1480 Transmitting INPUTS INPUTS OUTPUTS OUTPUTS RE DE DI B A RE DE A–B RO X 1 1 0 1 0 0 ≥ 0.2V 1 0 ≤ – 0.2V 0 X 1 0 1 0 0 0 0 X Z Z 0 0 Inputs Open 1 1 0 X Z* Z* 1 0 X Z* *Shutdown mode *Shutdown mode TEST CIRCUITS A VOD 1k VCC VOC R S1 TEST POINT RECEIVER OUTPUT R 1k CRL S2 B LTC1480 • F02 LTC1480 • F01 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 3V DE A DI LTC1480 DRIVER CL1 RDIFF B CL2 A S1 LTC1480 B RECEIVER RE RO 15pF VCC 500Ω OUTPUT UNDER TEST S2 CL LTC1480 • F03 LTC1480 • F04 Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load U W W SWITCHI G TI E WAVEFOR S 3V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DI 1.5V 0V t PLH 1/2 VO t PHL B VO A VO 0V –VO tSKEW 1/2 VO 90% 10% tr t SKEW 90% 10% VDIFF = V(A) – V(B) tf LTC1480 • F05 Figure 5. Driver Propagation Delays 5 LTC1480 U W W SWITCHI G TI E WAVEFOR S 3V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 1.5V DE 1.5V 0V t LZ t ZL(SHDN), t ZL 3.3V A, B VOL 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOH A, B 0V t HZ t ZH(SHDN), t ZH LTC1480 • F06 Figure 6. Driver Enable and Disable Times VOH 1.5V RO VOL f = 1MHz, tr ≤ 10ns, tf ≤ 10ns t PHL VOD2 A–B –VOD2 1.5V OUTPUT 0V t PLH 0V INPUT LTC1480 • F07 Figure 7. Receiver Propagation Delays 3V 1.5V RE 3.3V RO VOL t ZL(SHDN), tZL t LZ 1.5V OUTPUT NORMALLY LOW 0.5V 1.5V OUTPUT NORMALLY HIGH 0.5V VOH RO 1.5V f = 1MHz, tr ≤ 10ns, tf ≤ 10ns 0V 0V t HZ t ZH(SHDN), tZH LTC1480 • F08 Figure 8. Receiver Enable and Disable Times U U W U APPLICATIO S I FOR ATIO VCC CMOS Output Driver The LTC1480 transceiver provides full RS485 compatibility while operating from a single 3.3V supply. The RS485 specification requires that a transceiver withstand common-mode voltages of up to 12V or –7V at the RS485 line connections. Additionally, the transceiver must be immune to both ESD and latch-up, This rules out traditional CMOS drivers, which include parasitic diodes from their driver outputs to each supply rail (Figure 9). The LTC1480 uses a proprietary process enhancement which adds a pair of Schottky diodes to the output stage (Figure 10), preventing current from flowing when the common-mode 6 VCC SD3 P1 P1 D1 D1 OUTPUT OUTPUT LOGIC N1 D2 LTC1480 • F10 Figure 9. Conventional CMOS Output Stage LOGIC SD4 N1 D2 LTC1480 • F09 Figure 10. LTC1480 Output Stage LTC1480 U U W U APPLICATIO S I FOR ATIO voltage exceeds the supply rails. Latch-up at the output drivers is virtually eliminated and the driver is prevented from loading the line under RS485 specified fault conditions. A proprietary output protection structure protects the transceiver line terminals against ESD strikes of up to ±10kV. When two or more drivers are connected to the same transmission line, a potential condition exists whereby more than two drivers are simultaneously active. If one or more drivers is sourcing current while another driver is sinking current, excessive power dissipation may occur within either the sourcing or sinking element. This condition is defined as driver contention, since multiple drivers are competing for one transmission line. The LTC1480 provides a current limiting scheme to prevent driver contention failure. When driver contention occurs, the current drawn is limited to about 70mA preventing excessive power dissipation within the drivers. The LTC1480 has a thermal shutdown feature which protects the part from excessive power dissipation. Under extreme fault conditions, up to 250mA can flow through the part causing rapid internal temperature rise. The thermal shutdown circuit will disable the driver outputs when the internal temperature reaches 150°C and turns them back on when the temperature cools to 130°C. This cycle will repeat as necessary until the fault condition is removed. Receiver Inputs The LTC1480 features an input common-mode range covering the entire RS485 specified range of –7V to 12V. Differential signals of greater than ±200mV within the specified input common-mode range will be converted to a TTL compatible signal at the receiver output. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the receiver inputs are floating (unterminated) an internal pull-up of 10µA at the A input will force the receiver output to a known high state. Low Power Operation The LTC1480 draws very little supply current whenever the driver outputs are disabled. In shutdown mode the quiescent current is typically less than 1µA. With the receiver active and the driver outputs disabled, the LTC1480 will typically draw 300µA quiescent current. With the driver outputs enabled but unterminated, quiescent current will rise as one of the two outputs sources current into the internal receiver input resistance. With the minimum receiver input resistance of 12k and the maximum output swing of 3.3V, the quiescent current will rise by a maximum of 275µA. Typical quiescent current rise with the driver enabled is about 100µA. The quiescent current rises significantly if the driver is enabled when it is externally terminated. With 1/2 termination load (120Ω between the driver outputs) the quiescent current will jump to at least 13mA as the drivers force a minimum of 1.5V across the termination resistance. With a fully terminated 60Ω line attached, the current will rise to greater than 25mA with the driver enabled, completely overshadowing the extra 100µA drawn by internal receiver inputs. Shutdown Mode Both the receiver output (RO) and the driver outputs (A, B) can be placed in three-state mode by bringing RE HIGH and DE LOW respectively. In addition, the LTC1480 will enter shutdown mode when RE is HIGH and DE is LOW. In shutdown the LTC1480 typically draws only 1µA of supply current. In order to guarantee that the part goes into shutdown, RE must be high and DE must be LOW for at least 600ns simultaneously. If this time duration is less than 50ns the part will not enter shutdown mode. Propagation Delay Many digital encoding schemes are dependent upon the difference in the propagation delay times of the driver and receiver. Figure 11 shows the test circuit for the LTC1480 propagation delay. The receiver delay times are: tPLH – tPHL = 13ns Typ, VCC = 3.3V The driver’s skew times are: tSKEW = 10ns Typ, VCC = 3.3V 20ns Max, VCC = 3.3V, TA = – 40°C to 85°C 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 circuits as described herein will not infringe on existing patent rights. 7 LTC1480 U U W U APPLICATIO S I FOR ATIO 100pF BR TTL IN t r, t f < 6ns D R R 100Ω RECEIVER OUT LTC1480 • F11 100pF Figure 11. Receiver Propagation Delay Test Circuit U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( +0.025 0.325 –0.015 8.255 +0.635 –0.381 ) 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.400* (10.160) MAX 0.065 (1.651) TYP 0.125 (3.175) MIN 0.045 ± 0.015 (1.143 ± 0.381) 0.015 (0.380) MIN 7 6 1 2 3 5 0.255 ± 0.015* (6.477 ± 0.381) 0.018 ± 0.003 (0.457 ± 0.076) 0.100 ± 0.010 (2.540 ± 0.254) 8 4 N8 0694 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm). S8 Package 8-Lead Plastic SOIC 0.189 – 0.197* (4.801 – 5.004) 8 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 6 5 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 7 0.150 – 0.157* (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.270) BSC SO8 0294 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm). 1 2 3 4 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 5V Low Power RS485 Interface Transceiver Low power LTC1481 5V Ultra-Low Power RS485 Transceiver with Shutdown Lowest power LTC1483 5V Ultra-Low Power RS485 Low EMI Transceiver with Shutdown Low EMI/lowest power LTC1485 5V Differential Bus Transceiver Highest speed LTC1487 5V Ultra-Low Power RS485 with Low EMI Shutdown and High Input Impendance High input impendance/low EMI/lowest power 8 Linear Technology Corporation LT/GP 0695 10K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1995