LTC1483 Ultra-Low Power RS485 Low EMI Transceiver with Shutdown U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Low Power: ICC = 120µA Max with Driver Disabled ICC = 500µA Max with Driver Enabled, No Load 1µA Quiescent Current in Shutdown Mode Controlled Slew Rate Driver for Reduced EMI Single 5V Supply Drivers/Receivers Have ±10kV ESD Protection – 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 Pin Compatible with the LTC485 UO APPLICATI ■ ■ ■ S Battery-Powered RS485/RS422 Applications Low Power RS485/RS422 Transceiver Level Translator The LTC®1483 is an ultra-low power differential line transceiver designed for data transmission standard RS485 applications with extended common-mode range (– 7V to 12V). It will also meet the requirements of RS422. The LTC1483 features output drivers with controlled slew rate, decreasing the EMI radiated from the RS485 lines, and improving signal fidelity with misterminated lines. The CMOS design offers significant power savings over its bipolar counterparts without sacrificing ruggedness against overload or ESD damage. Typical quiescent current is only 80µA while operating and less than 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 over ±10kV. The LTC1483 is fully specified over the commercial and extended industrial temperature range and is available in 8-pin DIP and SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. UO TYPICAL APPLICATI RO1 R VCC1 RE1 RTERM DI DE1 DI1 D GND1 A–B RTERM RO2 R VCC2 RE2 RO DE2 DI2 D GND2 LTC1483 • TA01 1483 TA02 1 LTC1483 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage (VCC) .............................................. 12V Control Input Voltage ..................... – 0.5V to VCC + 0.5V Driver Input Voltage ....................... – 0.5V to VCC + 0.5V Driver Output Voltage ........................................... ±14V Receiver Input Voltage .......................................... ±14V Receiver Output Voltage ................ – 0.5V to VCC + 0.5V Operating Temperature Range LTC1483C........................................ 0°C ≤ TA ≤ 70°C LTC1483I .................................... – 40°C ≤ TA ≤ 85°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER LTC1483CN8 LTC1483IN8 LTC1483CS8 LTC1483IS8 TOP VIEW RO 1 8 VCC RE 2 7 B DE 3 6 A 5 GND DI 4 R D N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 130°C/ W (N8) TJMAX = 125°C, θJA = 150°C/ W (S8) S8 PART MARKING 1483 1483I Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS VCC = 5V, (Notes 2, 3) unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN VOD1 Differential Driver Output Voltage (Unloaded) IO = 0 ● VOD2 Differential Driver Output Voltage (with Load) R = 50Ω (RS422) R = 27Ω (RS485), Figure 1 ● ● TYP 2 1.5 MAX UNITS 5 V 5 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 ● 3 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 IIN1 Input Current DE, DI, RE ● ±2 µA IIN2 Input Current (A, B) DE = 0, VCC = 0V or 5.25V, VIN = 12V DE = 0, VCC = 0V or 5.25V, VIN = – 7V ● ● 1.0 – 0.8 mA mA VTH Differential Input Threshold Voltage for Receiver – 7V ≤ VCM ≤ 12V ● ∆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 2 V – 0.2 0.2 45 V mV 3.5 12 V V 25 kΩ 300 80 500 120 µA µA 1 10 µA 35 250 mA 35 250 mA 7 85 mA LTC1483 U SWITCHI G CHARACTERISTICS VCC = 5V, (Notes 2, 3) unless otherwise noted. LTC1483 TYP SYMBOL PARAMETER CONDITIONS MIN tPLH Driver Input to Output tPHL Driver Input to Output RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 3, 5) MAX UNITS ● 150 1200 ns ● 150 1200 ns tSKEW Driver Output to Output ● t r , tf Driver Rise or Fall Time ● 150 600 ns 1200 ns tZH Driver Enable to Output High CL = 100pF (Figures 4, 6), S2 Closed ● 100 1500 ns tZL Driver Enable to Output Low CL = 100pF (Figures 4, 6), S1 Closed ● 100 1500 ns tLZ Driver Disable Time from Low CL = 15pF (Figures 4, 6), S1 Closed ● 150 1500 ns tHZ Driver Disable Time from High CL = 15pF (Figures 4, 6), S2 Closed ● 150 1500 ns tPLH Receiver Input to Output 30 140 200 ns Receiver Input to Output RDIFF = 54Ω, CL1 = CL2 = 100pF, (Figures 3, 7) ● tPHL ● 30 140 200 ns tSKD tPLH – tPHL Differential Receiver Skew tZL Receiver Enable to Output Low tZH Receiver Enable to Output High tLZ Receiver Disable from Low tHZ Receiver Disable from High fMAX Maximum Data Rate tSHDN Time to Shutdown tZH(SHDN) tZL(SHDN) 100 ● 13 CRL = 15pF (Figures 2, 8), S1 Closed ● 20 50 ns CRL = 15pF (Figures 2, 8), S2 Closed ● 20 50 ns CRL = 15pF (Figures 2, 8), S1 Closed ● 20 50 ns CRL = 15pF (Figures 2, 8), S2 Closed ● 20 50 ● 250 DE = 0, RE = ● 50 Driver Enable from Shutdown to Output High CL = 100pF (Figures 4, 6), S2 Closed Driver Enable from Shutdown to Output Low CL = 100pF (Figures 4, 6), S1 Closed tZH(SHDN) Receiver Enable from Shutdown to Output High tZL(SHDN) Receiver Enable from Shutdown to Output Low ns ns kbits/s 600 ns ● 2000 ns ● 2000 ns CL = 15pF (Figures 2, 8), S2 Closed ● 3500 ns CL = 15pF (Figures 2, 8), S1 Closed ● 3500 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. 200 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 = 5V and TA = 25°C. U W TYPICAL PERFORMANCE CHARACTERISTICS Receiver tPLH – tPHL vs Temperature Supply Current vs Temperature 350 DRIVER ENABLED 200 150 100 DRIVER DISABLED 12 60 10 8 6 4 2 50 0 –50 –25 70 OUTPUT CURRENT (mA) tPLH – tPHL (ns) SUPPLY CURRENT (µA) 250 14 TA = 25°C THERMAL SHUTDOWN WITH DRIVER ENABLED 300 Driver Differential Output Voltage vs Output Current 0 25 50 75 100 125 150 175 TEMPERATURE (°C) 1483 G01 0 –50 –25 50 40 30 20 10 0 50 25 75 0 TEMPERATURE (°C) 100 125 1483 G02 0 1 2 4 3 OUTPUT VOLTAGE (V) 5 1483 G03 3 LTC1483 U W TYPICAL PERFORMANCE CHARACTERISTICS Driver Differential Output Voltage vs Temperature Driver Output Low Voltage vs Output Current 70 2.5 0 TA = 25°C RL = 54Ω 2.4 2.1 2.0 1.9 1.8 1.7 OUTPUT CURRENT (mA) 2.2 50 40 30 20 10 0 –25 50 25 0 75 TEMPERATURE (°C) 100 0 125 –20 –30 –40 –50 –60 –70 –80 1.6 1.5 –50 TA = 25°C –10 60 2.3 OUTPUT CURRENT (mA) DIFFERENTIAL VOLTAGE (V) Driver Output High Voltage vs Output Current 1 2 –90 4 3 0 OUTPUT VOLTAGE 1 3 2 OUTPUT VOLTAGE (V) 4 1483 G05 1483 G04 5 1483 G06 U U U PIN FUNCTIONS RO (Pin 1): Receiver Output. If the receiver output is enabled (RE low), then if A > B by 200mV, 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. 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. 4.75V < VCC < 5.25V. U U FU CTIO TABLES LTC1483 Transmitting LTC1483 Receiving INPUTS OUTPUTS INPUTS OUTPUTS RE DE DI B A RE DE A–B RO X 1 1 0 1 0 0 ≥ 0.2V 1 X 1 0 1 0 0 0 ≤ – 0.2V 0 0 0 X Z Z 0 0 Inputs Open 1 1 0 X Z* Z* 1 0 X Z* *Shutdown mode for LTC1483 4 *Shutdown mode for LTC1483 LTC1483 TEST CIRCUITS A 1k VCC VOD R S1 TEST POINT RECEIVER OUTPUT R VOC 1k CRL S2 B LTC1483 • F02 LTC1483 • F01 Figure 1. Driver DC Test Load Figure 2. Receiver Timing Test Load 3V DE A DI CL1 B CL2 RE VCC 500Ω OUTPUT UNDER TEST RO RDIFF B S1 A S2 CL 15pF LTC1483 • F04 LTC1483 • F03 Figure 3. Driver/Receiver Timing Test Circuit Figure 4. Driver Timing Test Load U W W SWITCHI G TI E WAVEFOR S 3V 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 t SKEW 90% 90% 10% VDIFF = V(A) – V(B) 10% tr LTC1483 • F05 tf Figure 5. Driver Propagation Delays 3V tr ≤ 10ns, tf ≤ 10ns 1.5V DE 1.5V 0V 5V A, B t ZL(SHDN), t ZL 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL VOH A, B t LZ 0V t ZH(SHDN), t ZH t HZ LTC1483 • F06 Figure 6. Driver Enable and Disable Times 5 LTC1483 U W W SWITCHI G TI E WAVEFOR S VOH 1.5V RO VOL tr ≤ 10ns, tf ≤ 10ns t PHL VOD2 A–B –VOD2 1.5V OUTPUT 0V t PLH 0V INPUT LTC1483 • F07 Figure 7. Receiver Propagation Delays 3V 1.5V RE 1.5V tr ≤ 10ns, tf ≤ 10ns 0V t ZL(SHDN), tZL 5V RO RO t LZ 1.5V OUTPUT NORMALLY LOW 0.5V 1.5V OUTPUT NORMALLY HIGH 0.5V 0V t HZ t ZH(SHDN), tZH LTC1483 • F08 Figure 8. Receiver Enable and Disable Times U U W U APPLICATIO S I FOR ATIO Basic Theory of Operation Traditionally RS485 transceivers have been designed using bipolar technology because the common-mode range of the device must extend beyond the supplies and the device must be immune to ESD damage and latch-up. Unfortunately, most bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption. The LTC1483 is a CMOS RS485/RS422 transceiver which features ultra-low power consumption without sacrificing ESD and latch-up immunity. The LTC1483 uses a proprietary driver output stage, which allows a common-mode range that extends beyond the power supplies while virtually eliminating latch-up and providing excellent ESD protection. Figure 9 shows the LTC1483 output stage while Figure 10 shows a conventional CMOS output stage. When the conventional CMOS output stage of Figure 10 enters a high impedance state, both the P-channel (P1) and the N-channel (N1) are turned off. If the output is then driven above VCC or below ground, the P+/N-well diode 6 (D1) or the N+/P-substrate diode (D2) respectively will turn on and clamp the output to the supply. Thus, the output stage is no longer in a high impedance state and is not able to meet the RS485 common-mode range requirement. In addition, the large amount of current flowing through either diode will induce the well-known CMOS latch-up condition, which could destroy the device. VCC VCC SD3 P1 P1 D1 D1 OUTPUT LOGIC N1 OUTPUT LOGIC SD4 D2 LTC1483 • F09 Figure 9. LTC1483 Output Stage N1 D2 LTC1483 • F10 Figure 10. Conventional CMOS Output Stage LTC1483 U U W U APPLICATIO S I FOR ATIO The LTC1483 output stage will maintain a high impedance state until the breakdown of the N-channel or P-channel is reached when going positive or negative respectively. The output will be clamped to either VCC or ground by a Zener voltage plus a Schottky diode drop, but this voltage is well beyond the RS485 operating range. An ESD cell protects output against multiple ±10kV human body model ESD strikes. Because the ESD injected current in the N-well or substrate consists of majority carriers, latch-up is prevented by careful layout techniques. Slew Rate The LTC1483 is designed for systems that are sensitive to electromagnetic radiation. The part features a slew rate limited driver that reduces high frequency electromagnetic emissions, while improving signal fidelity by reducing reflections due to misterminated cables. Figures 11 and 12 show the spectrum of the signal at the driver output for a standard slew rate RS485 driver and the slew rate limited LTC1483. The LTC1483 shows significant reduction of the high frequency harmonics. Because the driver is slew rate limited, the maximum operating frequency is limited to 250kbits/s. Low Power Operation The LTC1483 is designed to operate with a quiescent current of 120µA max. With the driver in three-state ICC will 20 10 LOG MAGNITUDE (dBVRMS) 0 –10 –20 –30 –40 –50 –60 –70 –80 0 1 2 3 4 5 FREQUENCY (MHz) Figure 11. Typical RS485 Driver Output Spectrum Transmitting at 150kHz 20 10 0 LOG MAGNITUDE (dBVRMS) The LTC1483 output stage of Figure 9 eliminates these problems by adding two Schottky diodes, SD3 and SD4. The Schottky diodes are fabricated by a proprietary modification to the standard N-well CMOS process. When the output stage is operating normally, the Schottky diodes are forward biased and have a small voltage drop across them. When the output is in the high impedance state and is driven above VCC or below ground, the parasitic diode D1 or D2 still turns on, but SD3 or SD4 will reverse bias and prevent current from flowing into the N-well or the substrate. Thus the high impedance state is maintained even with the output voltage beyond the supplies. With no minority carrier current flowing into the N-well or substrate, latch-up is virtually eliminated under power-up or power-down conditions. –10 –20 –30 –40 –50 –60 –70 –80 0 1 2 3 5 4 FREQUENCY (MHz) Figure 12. Slew Rate Limited LTC1483 Driver Output Spectrum Transmitting at 150kHz drop to this 120µA level. With the driver enabled there will be additional current drawn by the internal 12k resistor. Under normal operating conditions this additional current is overshadowed by the current drawn by the external bus impedance. 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 LTC1483 U U W U APPLICATIO S I FOR ATIO 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 LTC1483 will enter shutdown mode when RE is high and DE is low. In shutdown the LTC1483 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 U PACKAGE DESCRIPTION than 50ns the part will not enter shutdown mode. Toggling either RE or DE will wake the LTC1483 back up within 3.5µs. If the slow slew rate driver was active immediately prior to shutdown, the supply current will not drop to 1µA until the driver outputs have reached a steady state; this can take as long as 2.6µs under worst case conditions. If the driver was disabled prior to shutdown the supply current will drop to 1µA immediately. Dimension in inches (millimeters) unless otherwise noted. N Package 8-Lead Plastic DIP 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP +0.025 0.325 –0.015 8.255 +0.635 –0.381 ) 0.125 (3.175) MIN 0.005 (0.127) MIN 0.400* (10.160) MAX 0.130 ± 0.005 (3.302 ± 0.127) 0.015 (0.380) MIN 7 6 5 1 2 3 4 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 N8 0695 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S Package 8-Lead Plastic SOIC 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) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *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 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.228 – 0.244 (5.791 – 6.197) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 1 2 3 4 SO8 0695 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC485 5V Low Power RS485 Interface Transceiver Low Power LTC1480 3.3V Ultra-Low Power RS485 Transceiver World’s First 3V Powered 485 Transceiver with Low Power Consumption LTC1481 5V Ultra-Low Power RS485 Transceiver with Shutdown 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 1094 10K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1994