LTC2870/LTC2871 RS232/RS485 Multiprotocol Transceivers with Integrated Termination DESCRIPTION FEATURES n n n n n n n n n n n One RS485 and Two RS232 Transceivers 3V to 5.5V Supply Voltage 20Mbps RS485 and 500kbps RS232 Automatic Selection of Integrated RS485 (120Ω) and RS232 (5kΩ)Termination Resistors Half-/Full-Duplex RS485 Switching High ESD: ±26kV (LTC2870), ±16kV (LTC2871) Logic Loopback Mode 1.7V to 5.5V Logic Interface Supports Up to 256 RS485 Nodes RS485 Receiver Failsafe Eliminates UART Lockup Available in 28-Pin 4mm × 5mm QFN and TSSOP (LTC2870), and 38-Pin 5mm × 7mm QFN and TSSOP (LTC2871) APPLICATIONS n n n n n Flexible RS232/RS485/RS422 Interface Software Selectable Multiprotocol Interface Ports Point-of-Sale Terminals Cable Repeaters Protocol Translators The LTC®2870/LTC2871 are robust pin-configurable multiprotocol transceivers, supporting RS232, RS485, and RS422 protocols, operating on a single 3V to 5.5V supply. The LTC2870 can be configured as two RS232 single-ended transceivers or one RS485 differential transceiver on shared I/O lines. The LTC2871 offers independent control of two RS232 transceivers and one RS485 transceiver, each on dedicated I/O lines. Pin-controlled integrated termination resistors allow for easy interface reconfiguration, eliminating external resistors and control relays. Half-duplex switches allow four-wire and two-wire RS485 configurations. Loopback mode steers the driver inputs to the receiver outputs for diagnostic self-test.The RS485 receivers support up to 256 nodes per bus, and feature full failsafe operation for floating, shorted or terminated inputs. An integrated DC/DC boost converter uses a small inductor and one capacitor, eliminating the need for multiple supplies for driving RS232 levels. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATIONS Protocol Switching with Automatic Termination Selection 1.7V TO VCC VL RS232 RS485 3V TO 5.5V LTC2870 Simultaneous Protocols and RS485 Termination Switching 1.7V TO VCC VL VCC 485/232 RS485 TERMINATION DY 3V TO 5.5V LTC2871 RS485 Duplex Switching 1.7V TO VCC VCC VL 3V TO 5.5V LTC2870, LTC2871 VCC TE485 Y OFF ON 120Ω Y DI DI, Z Z DY A DZ RO A B RB RS485 FULL HALF DIN1 ROUT1 DIN2 ROUT2 Z 120Ω B RA Y DOUT1 RIN1 DOUT2 H/F DUPLEX RO, RB A B RIN2 28701 TA01 28701f 1 LTC2870/LTC2871 ABSOLUTE MAXIMUM RATINGS (Notes 1 and 2) Input Supplies VCC, VL..................................................... –0.3V to 7V Generated Supplies VDD ................................................ VCC – 0.3V to 7.5V VEE ......................................................... 0.3V to –7.5V VDD – VEE..............................................................15V SW ........................................... –0.3V to (VDD + 0.3V) CAP............................................. 0.3V to (VEE – 0.3V) A, B, Y, Z, RIN1, RIN2, DOUT1, DOUT2 ........–15V to 15V DI, DZ, DY, RXEN, DXEN, LB, H/F, TE485, RX485, DX485, RX232, DX232, DIN1, DIN2, 485/232, CH2........................................... –0.3V to 7V FEN, RA, RB, RO, ROUT1, ROUT2 ...–0.3V to (VL + 0.3V) Differential Enabled Terminator Voltage (A-B or Y-Z) ..........................................................±6V Operating Temperature LTC2870C/LTC2871C ............................... 0°C to 70°C LTC2870I/LTC2871I ............................. –40°C to 85°C Storage Temperature Range .................. –65°C to 125°C Lead Temperature (Soldering, 10 sec) FE package........................................................ 300°C PIN CONFIGURATION LTC2870 LTC2870 TOP VIEW GND VCC VL LB H/F TE485 TOP VIEW 28 27 26 25 24 23 VEE 1 22 A RA 2 21 B RB 3 20 VCC 485/232 4 19 Y 29 VEE RXEN 5 18 GND 17 Z DXEN 6 LB 1 28 VL H/F 2 27 VCC TE485 3 26 GND VEE 4 25 A RA 5 24 B 23 VCC RB 6 485/232 7 RXEN 8 DXEN 9 29 VEE 22 Y 21 GND 20 Z DY 7 16 VCC DY 10 19 VCC DZ 8 15 VDD DZ 11 18 VDD FEN 12 17 SW GND 13 16 GND CAP 14 15 VEE SW GND VEE CAP FEN GND 9 10 11 12 13 14 UFD PACKAGE 28-LEAD (4mm s 5mm) PLASTIC QFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 29) IS VEE, MUST BE SOLDERED TO PCB FE PACKAGE 28-LEAD PLASTIC TSSOP TJMAX = 125°C, θJA = 25°C/W EXPOSED PAD (PIN 29) IS VEE, MUST BE SOLDERED TO PCB 28701f 2 LTC2870/LTC2871 PIN CONFIGURATIONS LTC2871 LTC2871 TOP VIEW VL 1 38 RO 35 RIN1 34 RIN2 VCC 4 RO TE485 VL 36 GND 38 37 36 35 34 33 32 LB 27 VCC 3 H/F 2 H/F TE485 LB GND TOP VIEW VEE 1 31 RIN1 VEE 5 ROUT1 2 30 RIN2 ROUT1 6 33 A ROUT2 3 29 A ROUT2 7 32 B CH2 4 28 B CH2 8 RX485 9 31 VCC 30 Y RX485 5 27 VCC DX485 6 26 Y 39 VEE DI 7 DX485 10 25 GND DI 11 24 Z DIN1 8 23 DOUT1 DIN2 9 DX232 10 22 DOUT2 RX232 11 21 VCC 20 VDD VEE 12 VEE SW GND VEE CAP FEN GND 13 14 15 16 17 18 19 UHF PACKAGE 38-LEAD (5mm s 7mm) PLASTIC QFN 39 VEE 29 GND 28 Z DIN1 12 27 DOUT1 DIN2 13 26 DOUT2 DX232 14 25 VCC RX232 15 VEE 16 24 VDD 23 VEE FEN 17 22 SW GND 18 21 GND CAP 19 20 VEE FE PACKAGE 38-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 29°C/W EXPOSED PAD (PIN 39) IS VEE, MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 34°C/W EXPOSED PAD (PIN 39) IS VEE, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2870CFE#PBF LTC2870IFE#PBF LTC2870CFE#TRPBF LTC2870IFE#TRPBF LTC2870FE LTC2870FE 28-Lead Plastic TSSOP 28-Lead Plastic TSSOP 0°C to 70°C –40°C to 85°C LTC2870CUFD#PBF LTC2870IUFD#PBF LTC2870CUFD#TRPBF LTC2870IUFD#TRPBF 2870 2870 28-Lead (4mm × 5mm) Plastic QFN 28-Lead (4mm × 5mm) Plastic QFN 0°C to 70°C –40°C to 85°C LTC2871CFE#PBF LTC2871IFE#PBF LTC2871CFE#TRPBF LTC2871IFE#TRPBF LTC2871FE LTC2871FE 38-Lead Plastic TSSOP 38-Lead Plastic TSSOP 0°C to 70°C –40°C to 85°C LTC2871CUHF#PBF LTC2871IUHF#PBF LTC2871CUHF#TRPBF LTC2871IUHF#TRPBF 2871 2871 38-Lead (5mm × 7mm) Plastic QFN 38-Lead (5mm × 7mm) Plastic QFN 0°C to 70°C –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ PRODUCT SELECTION GUIDE PART NUMBER CONFIGURABLE TRANSCEIVER COMBINATIONS (RS485 + RS232) PACKAGES LTC2870 (0 + 0), (1 + 0), (0 + 2) 28-Lead QFN, 28-Lead TSSOP LTC2871 (0 + 0), (1 + 0), (1 + 1), (1 + 2), (0 + 1), (0 + 2) 38-Lead QFN, 38-Lead TSSOP 28701f 3 LTC2870/LTC2871 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Power Supply VCC Supply Voltage Operating Range VL Logic Supply Voltage Operating Range VL ≤ VCC VCC Supply Current in Shutdown Mode RXEN = VL, DXEN = TE485 = FEN = 0V, (LTC2870) DX485 = DX232 = TE485 = FEN = H/F = 0V, RX485 = RX232 = VL (LTC2871) VCC Supply Current in Transceiver Mode (Outputs Unloaded) (Note 3) 485/232 = DXEN = VL, RXEN = 0V, DY/DZ = 0V or VL (LTC2870) DX485 = DX232 = VL, RX485 = RX232 = 0V, DI/DIN1/DIN2 = 0V or VL (LTC2871) VL Supply Current in Transceiver Mode (Outputs Unloaded) 3 5.5 V 1.7 VCC V 60 μA l 8 3.3 l 0 mA 5 μA 6 VCC VCC V V V RS485 Driver |VOD| Differential Output Voltage RL = ∞, VCC = 3V (Figure 1) RL = 27Ω, VCC = 3V (Figure 1) RL = 50Ω, VCC = 3.13V (Figure 1) l l l Δ|VOD| Difference in Magnitude of Differential Output Voltage for Complementary Output States RL = 27Ω, VCC = 3V (Figure 1) RL = 50Ω, VCC = 3.13V (Figure 1) l l 0.2 0.2 V V VOC Common Mode Output Voltage RL = 27Ω or 50Ω (Figure 1) l 3 V Δ|VOC| Difference in Magnitude of Common Mode Output Voltage for Complementary Output States RL = 27Ω or 50Ω (Figure 1) l 0.2 V IOZD485 Three-State (High Impedance) Output Current VOUT = 12V or –7V, VCC = 0V or 3.3V (Figure 2) l –100 125 μA –7V ≤ VOUT ≤ 12V (Figure 2) l –250 250 mA 125 μA IOSD485 Maximum Short-Circuit Current 1.5 1.5 2 RS485 Receiver IIN485 Input Current VIN = 12V or –7V, VCC = 0V or 3.3V (Figure 3) (Note 5) l –100 RIN485 Input Resistance VIN = 12V or –7V, VCC = 0V or 3.3V (Figure 3) (Note 5) l 96 Differential Input Signal Threshold Voltage (A-B) –7V ≤ (A or B) ≤ 12V (Note 5) l Input Hysteresis B = 0V (Notes 3, 5) Differential Input Failsafe Threshold Voltage –7V ≤ (A or B) ≤ 12V (Note 5) Input DC Failsafe Hysteresis B = 0V (Note 5) Output Low Voltage Output Low, I(RA, RO) = 3mA (Sinking), 3V ≤ VL ≤ 5.5V l 0.4 V Output Low, I(RA, RO) = 1mA (Sinking), 1.7V ≤ VL < 3V l 0.4 V Output High, I(RA, RO) = –3mA (Sourcing), 3V ≤ VL ≤ 5.5V l VL – 0.4 V Output High, I(RA, RO) = –1mA (Sourcing), 1.7V ≤ VL < 3V l VL – 0.4 V Three-State (High Impedance) Output Current 0V ≤ (RA, RO), ≤VL, VL = 5.5V l Short-Circuit Output Current 0V ≤ (RA, RO), ≤VL, VL = 5.5V l VOL VOH Output High Voltage 125 kΩ ±200 mV 0 mV 130 l –200 –50 mV 25 0 mV ±5 μA ±125 mA 28701f 4 LTC2870/LTC2871 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. SYMBOL PARAMETER RTERM Terminating Resistor CONDITIONS MIN TYP MAX UNITS TE485 = VL, A – B = 2V, B = –7V, 0V, 10V (Figure 8) (Note 5) l 108 120 156 Ω RS232 Driver VOLD Output Low Voltage RL = 3kΩ; VEE ≤ –5.9V l –5 –5.7 –7.5 V VOHD Output High Voltage RL = 3kΩ; VDD ≥ 6.5V l 5 6.2 7.5 V Three-State (High Impedance) Output Current Y or Z (LTC2870) = ±15V RS232 Receiver Enabled DOUT1 or DOUT2 (LTC2871) = ±15V l ±156 μA l ±10 μA Driver Output = 0V l ±35 ±90 mA Output Short-Circuit Current RS232 Receiver Input Threshold Voltage l 0.6 1.5 2.5 V Input Hysteresis l 0.1 0.4 1.0 V 0.4 V Output Low Voltage I(RA, RB, ROUT1, ROUT2) = 1mA (Sinking) 1.7V ≤ VL ≤ 5.5V l Output High Voltage I(RA, RB, ROUT1, ROUT2) = –1mA (Sourcing) 1.7V ≤ VL ≤ 5.5V l VL – 0.4 Input Resistance –15V ≤ (A, B, RIN1, RIN2) ≤ 15V, RS232 Receiver Enabled l 3 Three-State (High Impedance) Output Current 0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL Output Short-Circuit Current VL = 5.5V 0V ≤ (RA, RB, ROUT1, ROUT2) ≤ VL V 5 7 kΩ l 0 ±5 μA l ±25 ±50 mA Logic Inputs Threshold Voltage l Input Current l 0.4 0 0.75 • VL V ±5 μA Power Supply Generator VDD Regulated VDD Output Voltage VEE Regulated VEE Output Voltage RS232 Drivers Enabled, Outputs Loaded with RL = 3kΩ to GND, DIN1/DY = VL, DIN2/DZ = 0V (Note 3) 7 V –6.3 V Human Body Model to GND or VCC, Powered or Unpowered (Note 7) ±26 kV ±16 kV Human Body Model (Note 7) ±4 kV ESD LTC2870 Interface Pins (A, B, Y, Z) LTC2871 Interface Pins (A, B, Y, Z, RIN1, RIN2, DOUT1, DOUT2) All Other Pins 28701f 5 LTC2870/LTC2871 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = VL = 3.3V, TE485 = 0V, LB = 0V unless otherwise noted. VL ≤ VCC. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS RS485 AC Characteristics Maximum Data Rate (Note 3) l Driver Propagation Delay RDIFF = 54Ω, CL = 100pF (Figure 4) l 20 70 ns Driver Propagation Delay Difference |tPLHD485 – tPHLD485| RDIFF = 54Ω, CL = 100pF (Figure 4) l 1 6 ns tSKEWD485 Driver Skew (Y to Z) RDIFF = 54Ω, CL = 100pF (Figure 4) l 1 ±6 ns tRD485, tFD485 Driver Rise or Fall Time RDIFF = 54Ω, CL = 100pF (Figure 4) l 15 ns tZLD485, tZHD485, tLZD485, tHZD485 Driver Output Enable or Disable Time FEN = VL, RL = 500Ω, CL = 50pF (Figure 5) l 120 ns tZHSD485, tZLSD485 Driver Enable from Shutdown RL = 500Ω, CL = 50pF (Figure 5) l 8 μs tPLHR485, tPHLR485 Receiver Input to Output CL = 15pF, VCM = 1.5V, |A – B| = 1.5V (Figure 6) (Note 5) l 65 85 ns tPLHD485 tPHLD485 20 Mbps tSKEWR485 Differential Receiver Skew |tPLHR485 – tPHLR485| CL = 15pF (Figure 6) l 1 6 ns tRR485, tFR485 Receiver Output Rise or Fall Time CL = 15pF (Figure 6) l 3 15 ns tZLR485, tZHR485, tLZR485, tHZR485 Receiver Output Enable or Disable Time FEN = VL, RL = 1kΩ, CL = 15pF (Figure 7) l 50 ns tRTEN485, tRTZ485 Termination Enable or Disable Time FEN = VL, VB = 0V, VAB = 2V (Figure 8) (Note 5) l 100 μs Maximum Data Rate RL = 3kΩ, CL = 2500pF RL = 3kΩ, CL = 500pF (Note 3) l l 100 500 Driver Slew Rate (Figure 9) RL = 3kΩ, CL = 2500pF RL = 3kΩ, CL = 50pF l l 4 RL = 3kΩ, CL = 50pF (Figure 9) l RS232 AC Characteristics tPHLD232, tPLHD232 Driver Propagation Delay kbps kbps 1 30 V/μs V/μs 2 μs tSKEWD232 Driver Skew RL = 3kΩ, CL = 50pF (Figure 9) tZLD232, tZHD232, tLZD232, tHZD232 Driver Output Enable or Disable Time FEN = VL, RL = 3kΩ, CL = 50pF (Figure 10) l 0.4 2 μs CL = 150pF (Figure 11) l 60 200 ns tPHLR232, tPLHR232 Receiver Propagation Delay 50 ns tSKEWR232 Receiver Skew CL = 150pF (Figure 11) tRR232, tFR232 Receiver Rise or Fall Time CL = 150pF (Figure 11) l 60 200 ns FEN = VL, RL = 1kΩ, CL = 150pF (Figure 12) l 0.7 2 μs FEN = l 0.2 2 ms tZLR232, tZHR232, tLZR232, tHZR232 Receiver Output Enable or Disable Time 25 ns Power Supply Generator VDD /VEE Supply Rise Time , (Notes 3 and 4) Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to device ground unless otherwise specified. Note 3: Guaranteed by other measured parameters and not tested directly. Note 4: Time from FEN until VDD ≥ 5V and VEE ≤ –5V. External components as shown in the Typical Application section. Note 5: Condition applies to A, B for H/F = 0V, and Y, Z for H/F = VL. Note 6: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Overtemperature protection activates at a junction temperature exceeding 150°C. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 7: Guaranteed by design and not subject to production test. 28701f 6 LTC2870/LTC2871 TYPICAL PERFORMANCE CHARACTERISTICS VCC Supply Current vs Supply Voltage in Shutdown Mode TA = 25°C, VCC = VL = 3.3V, unless otherwise noted. VCC Supply Current vs Supply Voltage in Fast Enable Mode 30 5 VCC Supply Current vs RS485 Data Rate 100 ALL DRIVERS AND RECEIVERS DISABLED TE485 LOW 80 H/F HIGH 20 15 H/F LOW 10 4 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) INPUT CURRENET (μA) 25 85°C 3 25°C –40°C 2 VCC = 5V VCC = 3.3V ALL RS485 DRIVERS AND RECEIVERS SWITCHING. CL = 100pF ON EACH DRIVER OUTPUT. 60 TE HIGH 40 20 5 TE LOW 0 3.5 3 4.5 4 INPUT VOLTAGE (V) 5 1 5.5 3 3.5 4 4.5 SUPPLY VOLTAGE (V) 20 2.5nF 0.5nF 15 0.05nF 4.5 ALL DRIVERS AND RECEIVERS SWITCHING. DRIVER OUTPUTS TIED TO RECEIVER INPUTS. RS232: 0.5Mbps (CL = 500pF) RS485: 20Mbps (CL = 100pF) TE485 HIGH 110 0.5nF 2.5nF 25 120 VCC = 5V VCC = 3.3V RS485 Driver Differential Output Voltage vs Temperature 100 3.5 90 –40°C 0 100 200 300 DATA RATE (kbps) 70 3 3.5 4 4.5 SUPPLY VOLTAGE (V) 5 VCC = 3.3V, VL = 1.7V VCC = 5V, VL = 1.7V VCC = 3.3V, VL = 3.3V VCC = 5V, VL = 5V 3.0 150 2.5 100 SKEW (ns) DELAY (ns) 1.5 1.0 0.5 –25 50 0 25 TEMPERATURE (°C) 75 100 28701 G06 0 25 50 TEMPERATURE (°C) 0 –50 –25 0 25 50 TEMPERATURE (°C) 100 75 RS485 Driver Short-Circuit Current vs Short-Circuit Voltage 2.0 10 –25 28701 G06 SHORT-CIRCUIT CURRENT (mA) 50 0 –50 0 –50 5.5 RS485 Driver Skew vs Temperature 20 VCC = 5V VCC = 3.3V 28701 G05 RS485 Driver Propagation Delay vs Temperature 30 RL = 54Ω 1.0 28701 G04 40 2.0 0.5 500 400 RL = 100Ω 2.5 85°C 0.05nF 5 RL = 54Ω 3.0 1.5 25°C 80 10 RL = 100Ω 4.0 VOLTAGE (V) INPUT CURRENT (mA) 30 100 28701 G03 VCC Supply Current vs Supply Voltage, All Transceivers at Max Rate (LTC2871) SUPPLY CURRENT (mA) ALL RS232 DRIVERS AND RECEIVERS SWITCHING. 1 10 DATA RATE (Mbps) 28701 G02 VCC Supply Current vs RS232 Data Rate 35 5.5 5 28701 G01 0 0.1 75 100 28701 G08 50 VCC = 5V VCC = 3.3V OUTPUT LOW 0 –50 OUTPUT HIGH –100 –150 –10 0 5 –5 10 SHORT-CIRCUIT VOLTAGE (V) 15 28701 G09 28701f 7 LTC2870/LTC2871 TYPICAL PERFORMANCE CHARACTERISTICS RS485 Receiver Propagation Delay vs Temperature RS485 Receiver Skew vs Temperature VCC = 3.3V, VL = 1.7V VCC = 5V, VL = 1.7V VCC = 3.3V, VL = 3.3V VCC = 5V, VL = 5V 70 RS485 Receiver Output Voltage vs Load Current 3.0 6 2.5 5 OUTPUT VOLTAGE (V) 80 TA = 25°C, VCC = VL = 3.3V, unless otherwise noted. SKEW (ns) DELAY (ns) 2.0 60 1.5 1.0 50 0.5 40 –50 0 25 50 TEMPERATURE (°C) –25 0 25 50 TEMPERATURE (°C) –25 6 INPUT LOW 1.2 4 3 2 0 25 50 TEMPERATURE (°C) 75 0 2 4 6 8 OUTPUT CURRENT (mA) 126 124 122 120 118 116 10 110 –50 RS232 Operation at 500kbps DIN1 5V/DIV DI 485/232 Y 1V/DIV 5V/DIV Y 5V/DIV 100 75 LTC2870 Drivers Changing Modes Z DOUT2 ROUT1 0 25 50 TEMPERATURE (°C) 28701 G15 RS485 Operation at 20Mbps DOUT1 –25 28701 G14 28701 G13 5V/DIV VCM = –7V VCM = 2V VCM = 12V 128 112 0 100 DIN2 10 114 1 VCC = 5V VCC = 3.3V 4 6 8 OUTPUT CURRENT (mA) 130 RESISTANCE (Ω) OUTPUT VOLTAGE (V) THRESHOLD VOLTAGE (V) 1.6 2 RS485 Termination Resistance vs Temperature VL = 5V VL = 3.3V VL = 1.7V 5 1.8 INPUT HIGH 0 28701 G12 RS232 Receiver Output Voltage vs Load Current 2.0 –25 2 28701 G11 RS232 Receiver Input Threshold vs Temperature 1.0 –50 3 0 100 75 28701 G10 1.4 4 1 0 –50 100 75 VL = 5V VL = 3.3V VL = 1.7V Z RS232 MODE RO RS485 MODE RS232 MODE ROUT2 1μs/DIV WRAPPING DATA DOUT LOADS: 5kΩ + 50pF 28701 G16 20ns/DIV H/F HIGH Y, Z LOADS: 120Ω (DIFF) + 50pF 28701 G17 2μs/DIV 28701 G18 28701f 8 LTC2870/LTC2871 TYPICAL PERFORMANCE CHARACTERISTICS RS232 Driver Outputs Enabling and Disabling TA = 25°C, VCC = VL = 3.3V, unless otherwise noted. VDD and VEE Powering Up VDD and VEE Ripple VDD RIPPLE DX232 2V/DIV DOUT1 FEN FEN = 1 10mV/DIV DOUT2 5V/DIV VEE RIPPLE VDD DOUT1 5V/DIV FEN = 0 DOUT2 40μs/DIV VEE 28701 G19 40μs/DIV 28701 G20 TOP CURVES: FAST ENABLE j DX232 BOTTOM CURVES: SHUTDOWN j DX232 28701 G21 40μs/DIV FAST ENABLE MODE, ALL DRIVERS AND RECEIVERS DISABLED. PIN FUNCTIONS PIN NAME LTC2870 QFN LTC2870 TSSOP LTC2871 QFN LTC2871 TSSOP DESCRIPTION VCC 16, 20, 24 19, 23, 27 21, 27, 33 25, 31, 37 Input Supply (3V to 5.5V). Tie all three pins together and connect a 2.2μF or larger capacitor between VCC (adjacent to VDD) and GND. VL 25 28 35 1 Logic Supply (1.7V to 5.5V) for the receiver outputs, driver inputs, and control inputs. Bypass this pin to GND with a 0.1μF capacitor if not tied tot VCC. Keep VL ≤ VCC for proper operation. However, VL > VCC will not damage the device, provided that absolute maximum limits are respected. VDD 15 18 20 24 Generated Positive Supply Voltage for RS232 Driver (+7V). Connect 1μF capacitor between VDD and GND. VEE 1, 12, 29 4, 15, 29 1, 12, 16, 19, 39 GND 10, 13, 18, 23 13, 16, 21, 26 14, 17, 25, 32 18, 21, 29, 36 CAP 11 14 15 19 Charge Pump Capacitor for Generated Negative Supply Voltage. Connect a 220nF capacitor between CAP and SW. SW 14 17 18 22 Switch Pin. Connect 10μH inductor between SW and VCC. A 22 25 29 33 RS485 Positive Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 1 (LTC2870). B 21 24 28 32 RS485 Negative Receiver Input (Full-Duplex Mode) or RS232 Receiver Input 2 (LTC2870). RA 2 5 RS485 Differential Receiver Output or RS232 Receiver Output 1. RB 3 6 RS232 Receiver Output 2. 5, 16, 20, Generated Negative Supply Voltage for RS232 Driver (–6.3V). Tie all pins together and 23, 39 connect 1μF capacitor between VEE (adjacent to the CAP pin) and GND. Ground. Tie all four pins together. RO 34 38 RS485 Differential Receiver Output. RIN1 31 35 RS232 Receiver Input 1. RIN2 30 34 RS232 Receiver Input 2. ROUT1 2 6 RS232 Receiver Output 1. ROUT2 3 7 RS232 Receiver Output 2. DIN1 8 12 RS232 Driver Input 1. DIN2 9 13 RS232 Driver Input 2. 28701f 9 LTC2870/LTC2871 PIN FUNCTIONS PIN NAME LTC2870 QFN LTC2870 TSSOP LTC2871 QFN LTC2871 TSSOP DESCRIPTION DOUT1 23 27 RS232 Driver Output 1. DOUT2 22 26 RS232 Driver Output 2. DI 7 11 RS485 Driver Input. DY 7 10 RS485 Driver Input or RS232 Driver Input 1. DZ 8 11 RS232 Driver Input 2. Y 19 22 26 30 RS485 Positive Driver Output. RS232 Driver Output 1 (LTC2870). RS485 Positive Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode). Z 17 20 24 28 RS485 Negative Driver Output or RS232 Driver Output 2 (LTC2870). RS485 Negative Receiver Input (LTC2870 or LTC2871 in Half-Duplex Mode). 485/232 4 7 Interface Select Input. A logic low enables RS232 mode and a high enables RS485 mode. The mode determines which transceiver inputs and outputs are accessible at the LTC2870 pins as well as which is controlled by the driver and receiver enable pins. RXEN 5 8 Receiver Enable. A logic high disables RS232 and RS485 receivers leaving receiver outputs Hi-Z. A logic low enables the RS232 or RS485 receivers, depending on the state of the interface select input 485/232 . DXEN 6 9 Driver Enable. A logic low disables the RS232 and RS485 drivers leaving the driver output in a Hi-Z state. A logic high enables the RS232 or RS485 drivers, depending on the state of the interface select input 485/232. RX232 11 15 RS232 Receiver Enable. A logic high disables the RS232 receivers and input termination resistors leaving the RS232 receiver outputs in a Hi-Z state. A logic low enables the RS232 receivers and resistors, subject to the state of the CH2 pin. RX485 5 9 RS485 Receiver Enable. A logic high disables the RS485 receiver leaving the RS485 receiver output in a Hi-Z state. A logic low enables the RS485 receiver and resistors, subject to the state of the CH2 pin. DX232 10 14 RS232 Driver Enable. A logic low disables the RS232 drivers leaving the RS232 driver outputs in a Hi-Z state. A logic high enables the RS232 drivers. DX485 6 10 RS485 Driver Enable. A logic low disables the RS485 driver leaving the RS485 driver output in a Hi-Z state. A logic high enables the RS485 driver. H/F 27 2 37 3 RS485 Half-Duplex Select Input. A logic low is used for full-duplex operation where pins A and B are the receiver inputs and pins Y and Z are the driver outputs. A logic high is used for half-duplex operation where pins Y and Z are both the receiver inputs and driver outputs and pins A and B do not serve as the receiver inputs. The impedance on A and B and state of differential termination between A and B is independent of the state of H/F. The H/F pin has no effect on RS232 operation. TE485 28 3 38 4 RS485 Termination Enable. A logic high enables a 120Ω resistor between pins A and B and also between pins Y and Z. A logic low opens the resistors, leaving A/B and Y/Z unterminated. The LTC2870 termination resistors are never enabled in RS232 mode. FEN 9 12 13 17 Fast Enable. A logic high enables fast enable mode. In fast enable mode the integrated DC/DC converter is active independent of the state of driver, receiver, and termination enable pins allowing faster circuit enable times than are otherwise possible. A logic low disables fast enable mode leaving the state of the DC/DC converter dependent on the state of driver, receiver, and termination enable control inputs. The DC/DC converter powers down only when FEN is low and all drivers, receivers, and terminators are disabled (refer to Table 1). LB 26 1 36 2 Loopback Enable. A logic high enables logic loopback diagnostic mode, internally routing the driver input logic levels to the receiver output pins. This applies to both RS232 channels as well as the RS485 driver/receiver. The targeted receiver must be enabled for the loopback signal to be available on its output. A logic low disables loopback mode. In Loopback mode, signals are not inverted from driver inputs to receiver outputs. 4 8 RS232 Channel 2 Disable. A logic high disables RS232 receiver 2 and RS232 driver 2 independent of the state of RX232 and DX232 pins. In this state, the disabled driver output becomes Hi-Z and the 5kΩ load resistor on the disabled receiver input is opened. A logic low allows both RS232 transceiver channels to be enabled or disabled together based on the RX232 and DX232 pins. CH2 28701f 10 LTC2870/LTC2871 BLOCK DIAGRAM LTC2870 1.7V TO 5.5V (≤ VCC) 3V TO 5.5V 10μH 0.1μF 220nF 2.2μF VL VCC SW CAP DXEN VDD RXEN VEE TE485 RT232 CONTROL LOGIC H/F RT485 485/232 PULSE-SKIPPING BOOST REGULATOR f = 1.2MHz 1μF 1μF FEN DRIVERS LB 232 DY Y RT485 485 120Ω Z 232 DZ LOOPBACK PATH 125k 125k H/F RECEIVERS RT232 232 5k A 125k RA RT485 485 5k 125k 120Ω B RB 232 GND 2870 BD 28701f 11 LTC2870/LTC2871 BLOCK DIAGRAM LTC2871 1.7V TO 5.5V (≤ VCC) 3V TO 5.5V 220nF 10μH 2.2μF 0.1μF VL VCC SW CAP DX232 DX485 VDD RX232 RX485 RT232 CONTROL LOGIC TE485 RT485 H/F VEE PULSE-SKIPPING BOOST REGULATOR f = 1.2MHz CH2 1μF 1μF FEN DRIVERS LB 232 DIN1 DOUT1 Y RT485 DI 485 120Ω Z DOUT2 232 DIN2 LOOPBACK PATH 125k 125k H/F RECEIVERS RT232 ROUT1 232 RIN1 5k A 125k RO RT485 485 120Ω 5k ROUT2 125k B RIN2 232 GND 2871 BD 28701f 12 LTC2870/LTC2871 TEST CIRCUITS Y OR Z Y GND OR VL DY/DI + RL GND DY/DI OR VL VOD DRIVER Z – RL + IOZD485, IOSD485 DRIVER + – Z OR Y VOUT VOC – 28701 F02 28701 F01 Figure 1. RS485 Driver DC Characteristics Figure 2. RS485 Driver Output Current IIN485 + – VIN RIN485 = A OR B B OR A RECEIVER VIN IIN485 28701 F03 Figure 3. RS485 Receiver Input Current and Resistance (Note 5) tPLHD485 DY/DI Y DY/DI RDIFF Z 0V tSKEWD485 CL DRIVER VL tPLHD485 Y, Z VOD ½VOD CL Y-Z 90% 10% 0V 0V tRD485 90% 10% tFD485 28701 F04 Figure 4. RS485 Driver Timing Measurement 28701f 13 LTC2870/LTC2871 TEST CIRCUITS RL Y VL DY/DI OR GND GND OR VCC DXEN/ DX485 VL ½VL ½VL tZLD485, tZLSD485 CL ½VCC Y OR Z DRIVER 0V tLZD485 VCC 0.5V VOL Z RL DXEN/DX485 VCC OR GND ½VCC Z OR Y 0V tHZD485 tZHD485, tZHSD485 CL VOH 0.5V 28701 F05 Figure 5. RS485 Driver Enable and Disable Timing Measurements VAB ±VAB/2 A-B A VCM RECEIVER 0V tPLHR485 RA/RO B CL ±VAB/2 RA/RO tPHLR485 90% 10% VL 90% ½VL ½VL tRR485 –VAB 10% tFR485 tSKEWR485 = tPLHR485 – tPHLR485 0V 28701 F06 Figure 6. RS485 Receiver Propagation Delay Measurements (Note 5) RXEN/ RX485 0V TO 3V VL ½VL ½VL tZLR485 B 0V tLZR485 A RECEIVER RA/RO 3V TO 0V RL VL OR GND ½VL RA/RO 0.5V CL RXEN/RX485 0.5V ½VL RA/RO tZHR485 VL tHZR485 VOL VOH 0V 28701 F07 Figure 7. RS485 Receiver Enable and Disable Timing Measurements (Note 5) 28701f 14 LTC2870/LTC2871 TEST CIRCUITS IA A RECEIVER TE485 RTERM = VAB VL IA TE485 + – ½VL ½VL 0V VAB tRTEN485 B 90% IA + – tRTZ485 10% VB 28701 F08 Figure 8. RS485 Termination Resistance and Timing Measurements (Note 5) DRIVER INPUT DRIVER OUTPUT DRIVER INPUT tPHLD232 ½VL tPLHD232 tF RL CL 3V DRIVER INPUT –3V SLEW RATE = VL ½VL 0V tR 0V 6V 0V 3V –3V VOHD VOLD tSKEWD232 = |tPHLD232 – tPLHD232| tF OR tR 28701 F09 Figure 9. RS232 Driver Timing and Slew Rate Measurements DRIVER OUTPUT 0V OR VL DXEN/DX232 RL DXEN/ DX232 VL ½VL ½VL 0V tZHD232 CL DRIVER OUTPUT tHZD232 tZLD232 DRIVER OUTPUT 0.5V 5V 0V tLZD232 5V VOHD 0V 0.5V VOLD 28701 F10 Figure 10. RS232 Driver Enable and Disable Times 28701f 15 LTC2870/LTC2871 TEST CIRCUITS RECEIVER OUTPUT RECEIVER INPUT RECEIVER INPUT +3V 1.5V 1.5V tPHLR232 CL RECEIVER OUTPUT 90% 10% –3V tPLHR232 ½VL ½VL VL 90% 10% tRR232 tFR232 tSKEWR232 = |tPLHR232 – tPHLR232| 0V 28701 F11 Figure 11. RS232 Receiver Timing Measurements RECEIVER OUTPUT RL –3V OR +3V RXEN/RX232 GND OR VL RXEN/ RX232 VL ½VL ½VL 0V tHZR232 tZHR232 CL RECEIVER OUTPUT tZLR232 RECEIVER OUTPUT 0.5V ½VL 0V tLZR232 ½VL VOHR VL 0.5V VOLR 28701 F12 Figure 12. RS232 Receiver Enable and Disable Times 28701f 16 LTC2870/LTC2871 FUNCTION TABLES Table 1. LTC2870 Mode Selection Table TE485 H/F LB DC/DC CONVERTER MODE AND COMMENTS 0 0 X X OFF Low Power Shutdown: All Main Functions Off 0 X X X OFF Low Power Shutdown: All Main Functions Off 1 0 0 X X ON Fast-Enable: DC/DC Converter On Only X 1 X X 0 ON RS232 Drivers On 0 0 X X X 0 ON RS232 Receivers On 1 X 1 X X 0 ON RS485 Driver On X 1 0 X X X 0 ON RS485 Receiver On X 1 X X 1 X X ON RS485 Driver and Receiver 120Ω Termination Enabled X 1 X X X 0 0 X RS485 Full-Duplex Mode X 1 X X X 1 0 X RS485 Half-Duplex Mode X 1 0 X X X 1 ON RS485 Loopback Mode X 0 0 X X X 1 ON RS232 Loopback Mode FEN 485/232 RXEN DXEN 0 X 1 0 0 1 1 X X 0 X X Table 2. LTC2871 Mode Selection Table (CH2 = 0) FEN RX232 DX232 RX485 DX485 TE485 H/F LB DC/DC CONVERTER MODE AND COMMENTS 0 1 0 1 0 0 X X OFF Low Power Shutdown: All Main Functions Off 1 1 0 1 0 0 X X ON Fast-Enable: DC/DC Converter On Only X X 1 X X X X 0 ON RS232 Drivers On X 0 X X X X X 0 ON RS232 Receivers On X X X X 1 X X 0 ON RS485 Driver On X X X 0 X X X 0 ON RS485 Receiver On X X X X X X 0 0 X RS485 Full-Duplex Mode X X X X X X 1 0 X RS485 Half-Duplex Mode X X X 0 X X X 1 ON RS485 Loopback Mode X 0 X X X X X 1 ON RS232 Loopback Mode Table 3. RS232 Receiver Mode (485/232 = 0 for LTC2870, CH2 = 0 for LTC2871) RX232 OR RXEN RECEIVER INPUTS (A, B, RIN1, RIN2) CONDITIONS RECEIVER OUTPUTS (RA, RB, ROUT1, ROUT2) LTC2870 RECEIVER INPUTS LTC2871 RECEIVER INPUTS (A, B) (RIN1, RIN2) 1 X No Fault Hi-Z 125kΩ Hi-Z 0 0 No Fault 1 5kΩ 5kΩ 0 1 No Fault 0 5kΩ 5kΩ 0 X Thermal Fault Hi-Z 5kΩ 5kΩ Table 4. RS232 Driver Mode (485/232 = 0 for LTC2870, CH2 = 0 for LTC2871) DX232 OR DXEN DRIVER INPUTS (DY, DZ, DIN1, DIN2) CONDITIONS LTC2870 DRIVER OUTPUTS (Y, Z) LTC2871 DRIVER OUTPUTS (DOUT1, DOUT2) 0 X No Fault 125kΩ Hi-Z 1 0 No Fault 1 1 1 1 No Fault 0 0 X X Thermal Fault 125kΩ Hi-Z 28701f 17 LTC2870/LTC2871 FUNCTION TABLES Table 5. LTC2871 CH2 CONTROL RS232 RECEIVER INPUTS RS232 DRIVER OUTPUTS CH2 DX232 RX232 RIN1 RIN2 DOUT1 DOUT2 X 0 1 Hi-Z Hi-Z Hi-Z Hi-Z Both Drivers and Receivers Disabled 0 0 0 5kΩ 5kΩ Hi-Z Hi-Z Both Receivers Enabled, Both Drivers Disabled 0 1 1 Hi-Z Hi-Z Driven Driven Both Receivers Disabled, Both Drivers Enabled 0 1 0 5kΩ 5kΩ Driven Driven 1 0 0 5kΩ Hi-Z Hi-Z Hi-Z Channel 2 Drivers and Receivers Disabled 1 1 1 Hi-Z Hi-Z Driven Hi-Z Channel 2 Drivers and Receivers Disabled 1 1 0 5kΩ Hi-Z Driven Hi-Z Channel 2 Drivers and Receivers Disabled COMMENTS Both Receivers and Drivers Enabled Table 6. RS485 Driver Mode (TE485 = 0) DX485 OR DXEN DI CONDITIONS Y Z 0 X No Fault 125kΩ 125kΩ 1 0 No Fault 0 1 1 1 No Fault 1 0 X X Thermal Fault 125kΩ 125kΩ Table 7. RS485 Receiver Mode (LB = 0) RXEN OR RX485 A - B (NOTE 5) CONDITIONS RA, RO 1 X No Fault Hi-Z 0 < –200mV No Fault 0 0 > 200mV No Fault 1 0 Inputs Open or Shorted Together (DC) Failsafe 1 X X Thermal Fault Hi-Z Table 8. RS485 Termination (485/232 = 1 for LTC2870) TE485 H/F, LB CONDITIONS R (A TO B) R (Y TO Z) 0 X No Fault Hi-Z Hi-Z 1 X No Fault 120Ω 120Ω X X Thermal Fault Hi-Z Hi-Z Table 9. RS485 Duplex Control (485/232 = 1 for LTC2870) H/F RS485 DRIVER OUTPUTS RS485 RECEIVER INPUTS 0 Y, Z A, B 1 Y, Z Y, Z Table 10. LTC2870 Loopback Functions Table 11. LTC2871 Loopback Functions LB RXEN MODE LB RX232 RX485 MODE 0 X Not Loopback 0 X X Not Loopback X 1 Not Loopback X 1 1 Not Loopback 1 0 Loopback (RA = DY, RB = DZ) 1 0 1 Loopback RS232 (ROUT1 = DIN1, ROUT2 = DIN2) 1 1 0 Loopback RS485 (R0 = DI) 1 0 0 Loopback All (ROUT1 = DIN1, ROUT2 = DIN2, RO = DI) 28701f 18 LTC2870/LTC2871 APPLICATIONS INFORMATION Overview The LTC2870 and LTC2871 are flexible multiprotocol transceivers supporting RS485/RS422 and RS232 protocols. These parts can be powered from a single 3V to 5.5V supply with optional logic interface supply as low as 1.7V. An integrated DC/DC converter provides the positive and negative supply rails needed for RS232 operation. Automatically selected integrated termination resistors for both RS232 and RS485 protocols are included, eliminating the need for external components and switching relays. Both parts include loopback control for self-test and debug as well as logically-switchable half- and full-duplex control of the RS485 bus interface. The LTC2870 offers a single port that can be configured as either two RS232 receivers and drivers or one RS485/ RS422 receiver and driver depending on the state of the 485/232 pin. Control inputs DXEN and RXEN provide independent control of driver and receiver operation for either RS232 or RS485 transceivers, depending on the selected operating protocol. The LTC2871 separates the RS232 and RS485 transceivers into independent I/Os allowing simultaneous operation of two RS232 transceivers and one RS485 transceiver. Independent control over driver and receiver mode for each protocol is provided with logic inputs DX232, RX232, DX485, RX485. Single channel RS232 operation is possible via the CH2 control pin. The disabled channel maintains a Hi-Z state on the receiver input and driver output, allowing these lines to be shared with other transceivers. Both parts feature rugged operation with ESD ratings of ±26kV (LTC2870) and ±16kV (LTC2871) HBM on the RS232 and RS485 receiver inputs and driver outputs, both unpowered and powered. All other pins offer protection exceeding ±4kV. DC/DC Converter The on-chip DC/DC converter operates from the VCC input, generating a 7V VDD supply and a charge pumped –6.3V VEE supply, as shown in Figure 13. VDD and VEE power the output stage of the RS232 drivers and are regulated to levels that guarantee greater than ±5V output swing. C1 220nF L1 10μH 3V TO 5.5V C4 2.2μF SW VCC CAP VDD C2 1μF PULSE-SKIPPING BOOST REGULATOR f = 1.2MHz VEE 28701 F13 C3 1μF Figure 13. DC/DC Converter The DC/DC converter requires a 10μH inductor (L1) and a bypass capacitor (C4) of 2.2μF. The charge pump capacitor (C1) is 220nF and the storage capacitors (C2 and C3) are 1μF. Larger storage capacitors up to 4.7μF may be used if C1 and C4 are scaled proportionately. Locate C1–C4 close to their associated pins. Up to two LTC2870 or LTC2871 devices can be powered from one of the devices; see Figure 48 in the Typical Applications section. Inductor Selection A 10μH inductor with a saturation current (ISAT) rating of at least 220mA and a DCR (copper wire resistance) of less than 1.3Ω is required. Some small inductors meeting these requirements are listed in Table 12. Table 12. Recommended Inductors PART NUMBER MAX ISAT (mA) DCR (Ω) LBC2016T100K CBC2016T100M 245 380 FSLB2520-100K 220 SIZE(mm) MANUFACTURER 1.07 1.07 2 × 1.6 × 1.6 2 × 1.6 × 1.6 Taiyo Yuden www.t-yuden.com 1.1 2.5 × 2 × 1.6 Toko www.tokoam.com Capacitor Selection The small size of ceramic capacitors makes them ideal for the LTC2870 and LTC2871. Use X5R or X7R dielectric types; their ESR is low and they retain their capacitance over relatively wide voltage and temperature ranges. Use a voltage rating of at least 10V. 28701f 19 LTC2870/LTC2871 APPLICATIONS INFORMATION Inrush Current and Supply Overshoot Precaution VL Logic Supply and Logic Pins In certain applications fast supply slew rates are generated when power is connected. If the VCC voltage is greater than 4.5V and its rise time is faster than 10μs, the pins VDD and SW can exceed their absolute maximum values during start-up. When supply voltage is applied to VCC, the voltage difference between VCC and VDD generates inrush current flowing through inductor L1 and capacitors C1 and C2. The peak inrush current must not exceed 2A. To avoid this condition, add a 1Ω resistor as shown in Figure 14. This precaution is not relevant for supply voltages below 4.5V or rise times longer than 10μs. A separate logic supply pin VL allows the LTC2870 and LTC2871 to interface with any logic signal from 1.7V to 5.5V. All logic I/Os use VL as their high supply. For proper operation, VL should not be greater than VCC. During power-up, if VL is higher than VCC, the device will not be damaged, but behavior of the device is not guaranteed. If VL is not connected to VCC, bypass VL with a 0.1μF capacitor to GND. Although all logic input pins reference VL as their high supply, they can be driven up to 7V, independent of VL and VCC, with the exception of FEN, which must not exceed VL by more than 1V for proper operation. Logic input pins do not have internal biasing devices to pull them up or down. They must be driven high or low to establish valid logic levels; do not float. 5V 0V ≤10μs R1 1Ω 1/8W C4 2.2μF L1 10μH C1 220nF INRUSH CURRENT SW RS232 and RS485 driver outputs are undriven and the RS485 termination resistors are disabled when VL or VCC is grounded or VCC is disconnected. CAP RS485 Driver VCC 28701 F14 VDD GND C2 1μF Figure 14. Supply Current Overshoot Protection for Input Supplies of 4.5V of Higher The RS485 driver provides full RS485/RS422 compatibility. When enabled, if DI is high, Y – Z is positive. With the driver disabled the Y and Z output resistance is greater than 96kΩ (typically 125kΩ) to ground over the entire common mode range of –7V to +12V. This resistance is equivalent to the input resistance on these lines when the driver is configured in half-duplex mode and Y and Z act as the RS485 receiver inputs. Driver Overvoltage and Overcurrent Protection The RS232 and RS485 driver outputs are protected from short circuits to any voltage within the absolute maximum range ±15V. The maximum current in this condition is 90mA for the RS232 driver and 250mA for the RS485 driver. If the RS485 driver output is shorted to a voltage greater than VCC, when it is active, positive current of up to 100mA may flow from the driver output back to VCC. If the system power supply or loading cannot sink this excess current, clamp VCC to GND with a Zener diode (e.g., 5.6V, 1W, 1N4734) to prevent an overvoltage condition on VCC. 28701f 20 LTC2870/LTC2871 APPLICATIONS INFORMATION All devices also feature thermal shutdown protection that disables the drivers, receivers, and RS485 terminators in case of excessive power dissipation (see Note 6). less than approximately 2μs. Increasingly slower signals will have increasingly less effective hysteresis, limited by the DC failsafe value of about 25mV. RS485 Balanced Receiver with Full Failsafe Operation The LTC2870 and LTC2871 provide full failsafe operation that guarantees the receiver output will be a logic high state when the inputs are shorted, left open, or terminated but not driven, for more than about 2μs. The delay allows normal data signals to transition through the threshold region without being interpreted as a failsafe condition. The LTC2870 and LTC2871 receivers use a window comparator with two voltage thresholds centered around zero for low pulse width distortion. As illustrated in Figure 15, for a differential signal approaching from a negative direction, the threshold is typically +65mV. When approaching from the positive direction, the threshold is typically –65mV. Each of these thresholds has about 25mV of hysteresis (not shown in the figure). The state of RO reflects the polarity of A–B in full-duplex mode or Y–Z in half-duplex mode. This windowing around 0V preserves pulse width and duty cycle for small input signals with heavily slewed edges, typical of what might be seen at the end of a very long cable. This performance is highlighted in Figure 16, where a signal is driven through 4000 feet of CAT5e cable at 3Mbps. Even though the differential signal peaks at just over ±100mV and is heavily slewed, the output maintains a nearly perfect signal with almost no duty cycle distortion. An additional benefit of the window comparator architecture is excellent noise immunity due to the wide effective differential hysteresis (or ‘AC’ hysteresis) of about 130mV for normal signals transitioning through the window region in RS485 Biasing Resistors Not Required RS485 networks are often biased with a resistive divider to generate a differential voltage of ≥200mV on the data lines, which establishes a logic high state when all the transmitters on the network are disabled. The values of the biasing resistors depend on the number and type of transceivers on the line and the number and value of terminating resistors. Therefore the values of the biasing resistors must be customized to each specific network installation, and may change if nodes are added to or removed from the network. The internal failsafe feature of the LTC2870 and LTC2871 eliminates the need for external biasing resistors. The LTC2870 and LTC2871 transceivers will operate correctly on unbiased, biased or underbiased networks. B 0.1V/DIV A RO (A-B) RECEIVER OUTPUT HIGH 0.1V/DIV RECEIVER OUTPUT LOW –200mV –65mV 0V 65mV 200mV VAB 28701 F15 Figure 15. RS485 Receiver Input Threshold Characteristics 5V/DIV RO 200ns/DIV 28701 F16 Figure 16. A 3Mbps Signal Driven Down 4000ft of CAT 5e Cable. Top Traces: Received Signals After Transmission Through Cable; Middle Trace: Math Showing Differences of Top Two Signals; Bottom Trace: Receiver Output 28701f 21 LTC2870/LTC2871 APPLICATIONS INFORMATION The RS232 and RS485 receiver outputs are internally driven high (to VL) or low (to GND) with no external pullup needed. When the receivers are disabled the output pin becomes Hi-Z with leakage of less than ±5μA for voltages within the VL supply range. RS485 Receiver Input Resistance The RS485 receiver input resistance from A or B to GND (Y or Z to GND in half-duplex mode with driver disabled) is greater than 96kΩ (typically 125kΩ) when the integrated termination is disabled. This permits up to a total of 256 receivers per system without exceeding the RS485 receiver loading specification. The input resistance of the receiver is unaffected by enabling/disabling the receiver or whether the part is in half-duplex, full-duplex, loopback mode, or even unpowered. The equivalent input resistance looking into the RS485 receiver pins is shown in Figure 17. 125k A 60Ω When the TE485 pin is high, the termination resistors are enabled and the differential resistance from A to B and Y to Z is 120Ω. The resistance is maintained over the entire RS485 common mode range of –7V to 12V as shown in Figure 18. 126 VCC = 5.0V VCC = 3.3V 124 122 120 118 TE485 125k through logic control, the proper line termination for correct operation when configuring transceiver networks. Termination should be enabled on transceivers positioned at both ends of the network bus. Termination on the driver nodes is important for cases where the driver is disabled but there is communication on the connecting bus from another node. Differential termination resistors are never enabled in RS232 mode on the LTC2870. RESISTANCE (Ω) Receiver Outputs 60Ω 116 –10 –5 0 5 VOLTAGE (V) 10 15 28701 F18 B 28701 F17 Figure 17: Equivalent RS485 Receiver Input Resistance Into A and B (Note 5) Selectable RS485 Termination Proper cable termination is important for good signal fidelity. When the cable is not terminated with its characteristic impedance, reflections cause waveform distortion. The LTC2870 and LTC2871 offer integrated switchable 120Ω termination resistors between the differential receiver inputs and also between the differential driver outputs. This provides the advantage of being able to easily change, Figure 18. Typical Resistance of the Enabled RS485 Terminator vs Common Mode Voltage on A /B RS485 Half- and Full-Duplex Control The LTC2870 and LTC2871 are equipped with a control to switch between half- and full-duplex operation. With the H/F pin set to a logic low, the A and B pins serve as the differential receiver inputs. With the H/F pin set to a logic high, the Y and Z pins serve as the differential inputs. In either configuration, the RS485 driver outputs are always on Y and Z. The impedance looking into the A and B pins is not affected by H/F control, including the differential termination resistance. The H/F control does not affect RS232 operation. 28701f 22 LTC2870/LTC2871 APPLICATIONS INFORMATION Logic Loopback A loopback mode connects the driver inputs to the receiver outputs (non-inverting) for self test. This applies to both RS232 and RS485 transceivers. Loopback mode is entered when the LB pin is high and the relevant receiver is enabled. In loopback mode, the drivers function normally. They can be disabled with outputs in a Hi-Z state or left enabled to allow loopback testing in normal operation. Loopback works in half- or full-duplex mode and does not affect the termination resistors. CABLE LENGTH (FT) 10k 1k LTC2870/LTC2871 MAX DATA RATE 100 RS485/RS422 MAX DATA RATE 10 10k 100k 1M 10M DATA RATE (bps) 100M 28701 F19 Figure 19. Cable Length vs Data Rate (RS485/RS422 Standard Shown in Vertical Solid Line) RS485 Cable Length vs Data Rate For a given data rate, the maximum transmission distance is bounded by the cable properties. A typical curve of cable length vs data rate compliant with the RS485/ RS422 standards is shown in Figure 19. Three regions of this curve reflect different performance limiting factors in data transmission. In the flat region of the curve, maximum distance is determined by resistive losses in the cable. The downward sloping region represents limits in distance and data rate due to AC losses in the cable. The solid vertical line represents the specified maximum data rate in the RS485/RS422 standards. The dashed lines at 20Mbps show the maximum data rates of the LTC2870 and LTC2871. Layout Considerations All VCC pins must be connected together on the PC board with very low impedance traces or with a dedicated plane. A 2.2μF or larger decoupling capacitor (C4 in Figure 13) must be placed less than 0.7cm away from the VCC pin that is adjacent to the VDD pin. 0.1μF capacitors to GND can be added on the VCC pins adjacent to the B and VL pins if the connection to the 2.2μF decoupling capacitor is not direct or if the trace is very narrow. All GND pins must be connected together and all VEE pins must be connected together, including the exposed pad on the bottom of the package. The bypass capacitor at VEE, C3, should be positioned closest to the VEE pin that is adjacent to the CAP pin, with no more than 1cm of total trace length between the VEE and GND pins. Place the charge pump capacitor, C1, directly adjacent to the SW and CAP pins, with no more than one centimeter of total trace length to maintain low inductance. Close placement of the inductor, L1, is of secondary importance compared to the placement of C1 but should include no more than two centimeters of total trace length. The PC board traces connected to high speed signals A/B and Y/Z should be symmetrical and as short as possible to minimize capacitive imbalance and maintain good differential signal integrity. To minimize capacitive loading effects, the differential signals should be separated by more than the width of a trace. Route outputs away from sensitive inputs to reduce feedback effects that might cause noise, jitter, or even oscillations. For example, do not route DI or A/B near the driver or receiver outputs. 28701f 23 LTC2870/LTC2871 TYPICAL APPLICATIONS VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state. VL VL DXEN LTC2870 485/232 VL DXEN RXEN LTC2870 485/232 DXEN RXEN LB LB DY DY Y LTC2870 H/F TE485 LB Y Y DY RA A RA A DZ Z DZ Z 120Ω Z A RA RB RB B Figure 20. LTC2870 in RS232 Mode GND DXEN 485/232 RXEN H/F LB 28701 F22 Figure 21. LTC2870 in RS232 Mode with Loopback TE485 Figure 22. LTC2870 in RS485 Mode, Terminated VL VL LTC2870 B 28701 F21 28701 F20 VL 120Ω B GND GND RXEN 485/232 DXEN LTC2870 485/232 RXEN DXEN TE485 485/232 LB H/F LTC2870 RXEN LB H/F Y Y TE485 DY DY Y Z Z DY 120Ω Z A A RA RA RA B 120Ω B GND GND 28701 F23 Figure 23. LTC2870 in RS485 Mode in Loopback GND 28701 F24 Figure 24. LTC2870 in RS485 Mode Half-Duplex 28701 F25 Figure 25. LTC2870 in RS485 Mode, Half-Duplex, with Loopback and Terminated 28701f 24 LTC2870/LTC2871 TYPICAL APPLICATIONS VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state. VL VL VL DXEN LTC2870 RXEN DX485 H/F RX232 TE485 LTC2871 LB RS RS 232 485 485/232 DY DX232 DX232 RX485 RX485 LTC2871 DX485 RX232 CH2 CH2 TE485 TE485 H/F H/F LB LB Y Y DI 120Ω DZ Z RA A Z DIN1 A ROUT1 B DIN2 DOUT1 RIN1 RO ROUT2 120Ω RIN2 B RB GND Figure 26. LTC2870 Protocol Switching VL LTC2871 GND GND 28701 F26 DX232 DOUT2 DX485 28701 F28 28701 F27 Figure 27. LTC2871 in RS485 Mode Figure 28. LTC2871 in RS232 Mode VL VL DX232 LTC2871 RX232 DX232 CH2 DX485 RX485 RX232 CH2 TE485 RX485 LB H/F TE485 TE485 LB H/F DX485 LTC2871 RX232 CH2 RX485 H/F LB Y Y DI 120Ω DI Z Z DIN1 DOUT1 ROUT1 RIN1 A A RO B DIN1 120Ω RO B DIN1 DOUT1 DOUT1 ROUT1 RIN1 RIN1 ROUT1 DIN2 DIN2 ROUT2 RIN2 GND GND 28701 F29 Figure 29. LTC2871 Single RS232 Channel Active DOUT2 DOUT2 RIN2 ROUT2 GND 28701 F30 Figure 30. LTC2871 in RS485 and RS232 Mode 28701 F31 Figure 31. LTC2871 in RS485 and RS232 Mode with Loopback and RS485 Termination 28701f 25 LTC2870/LTC2871 TYPICAL APPLICATIONS VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state. VL VL VL H/F LTC2871 CH2 DX232 LB DX485 TE485 D R 485 DX485 LTC2871 RX232 DX232 CH2 DX485 H/F RX485 H/F LB TE485 TE485 LTC2871 RX232 CH2 RX485 LB RX485 DX232 D R 232 RX232 Y Y Y DI DI DI Z 120Ω Z Z A RO RO RO DIN1 DIN1 B DIN1 DOUT1 RIN1 ROUT1 RIN1 ROUT1 DIN2 DIN2 RIN2 RIN1 ROUT1 DIN2 DOUT2 RIN2 ROUT2 RIN2 ROUT2 GND GND GND 28701 F32 Figure 32. LTC2871 in RS485 and RS232 Mode, Both Half-Duplex DOUT1 DOUT2 DOUT2 ROUT2 120Ω DOUT1 28701 F34 28701 F33 Figure 33. LTC2871 in RS485 and RS232 Mode, RS485 Half-Duplex, Loopback Figure 34. LTC2871 in RS485 and RS232 Mode, RS485 Half-Duplex, Terminated VL 485/232 LTC2870/ LTC2871 H/F 3V TO 5.5V LB TE485 1.7V TO VCC LTC2870/ LTC2871 VCC VL LTC2870/ LTC2871 CONTROL SIGNALS Y DI Z DY RS485 FULL HALF DY, DIN1 Y RA, ROUT1 A DZ, DIN2 Z RB, ROUT2 B 120Ω H/F μP RS232 DUPLEX 28701 F37 A RO 120Ω B RB GND 28701 F36 GND Figure 36. Microprocessor Interface 28701 F35 DATA RATE CL 100kbps 5nF 500kbps 1nF CL 3k Figure 37. Driving Larger RS232 Loads Figure 35. RS485 Duplex Switching 28701f 26 LTC2870/LTC2871 TYPICAL APPLICATIONS 1.7V TO VCC VL VL 3V TO 5.5V LTC2870 VCC DXEN RXEN 485/232 H/F RS485 FULL-DUPLEX RS485 HALF-DUPLEX RS232 FULL-DUPLEX 485/232 = 1 H/F = 0 485/232 = 1 H/F = 1 485/232 = 0 H/F = X RS485 RS485 RS232 RS485 RS485 RS232 TE485 DY Y CONTROLLER Z DZ CONNECTOR RA A B RS485 RS232 RS485 RS232 RB GND 28701 F38 Figure 38. LTC2870: Making Use of Shared I/O for Various Communication Configurations 1.7V TO VCC VL VL 3V TO 5.5V LTC2870 DXEN VCC TE485 RXEN 485/232 H/F RS485 HALF-DUPLEX RS232 HALF-DUPLEX DY 485/232 = 1 H/F = 0 485/232 = 0 H/F = X RS485 RS232 RS485 RS232 Y CONTROLLER Z CONNECTOR DZ RA A B RB GND 28701 F39 Figure 39. LTC2870: Using External Connections for Half-Duplex RS232 or RS485 Operation 28701f 27 LTC2870/LTC2871 TYPICAL APPLICATIONS 1.7V TO VCC VL DX232 RX232 DX485 RX485 H/F TE485 VL 3V TO 5.5V LTC2871 VCC RS232 FULL-DUPLEX RS232 FULL-DUPLEX RS485 FULL-DUPLEX RS485 HALF-DUPLEX H/F = 0 H/F = 1 RS232 RS232 RS485 RS485 RS485 RS485 RS232 RS232 RS232 RS232 DOUT1 DIN1 Y DI Z CONTROLLER DOUT2 DIN2 CONNECTOR ROUT1 RIN1 RS485 A RO RS485 B ROUT2 RS232 RIN2 RS232 GND 28701 F40 Figure 40. LTC2871: Various Communication Configurations 1.7V TO VCC VL VL 3V TO 5.5V LTC2871 DX232 RX232 DX485 RX485 H/F TE485 DIN1 VCC DOUT1 Y DI Z CONTROLLER DOUT2 DIN2 RS232 HALF-DUPLEX RS232 HALF-DUPLEX RS485 FULL-DUPLEX RS485 HALF-DUPLEX H/F = 0 H/F = 1 RS232 RS232 RS485 RS485 RS485 RS485 RS232 RS232 CONNECTOR RIN1 ROUT1 A RO B RS485 RS485 RIN2 ROUT2 GND 28701 F41 Figure 41. LTC2871: More Communication Configurations Using External Connections 28701f 28 LTC2870/LTC2871 TYPICAL APPLICATIONS VCC = 3V to 5.5V, VL = 1.7V to VCC. Logic input pins not shown are tied to a valid logic state. VL VL DX232 LTC2871 RX232 RX232 LB DX485 LB RX485 CH2 DI 120Ω CH2 H/F Y A Z B TE485 RO 120Ω ROUT1 RXIN DIN1 RIN1 DOUT1 RS485 ROUT1 RIN1 ROUT1 DIN1 RO 120Ω RXOUT RS232 UP TO 4000 FT CAT5e CABLE RS232 DRIVER OUT DX232 DX485 RX485 H/F TE485 LTC2871 A Y B Z DI 120Ω GND DRIVER IN GND 28701 F42 Figure 42. RS232 Extension Cord Using RS232 to RS485 Conversion SLAVE SLAVE LTC2852 LTC2852 SLAVE MASTER LTC2870/LTC2871 LTC2855 120Ω 120Ω 120Ω 3.3V VL TE485 TE 28701 F43 Figure 43. RS485 Full-Duplex Network 28701f 29 LTC2870/LTC2871 TYPICAL APPLICATIONS LTC2871 DIN1 PORT 1 LOGIC INTERFACE ROUT1 RIN1 DIN2 PORT 2A/2B LOGIC INTERFACE LTC2871 DOUT1 DIN1 PORT 1 LINE INTERFACE PORT 1 LOGIC INTERFACE PORT 2A LINE INTERFACE PORT 2A LOGIC INTERFACE DOUT2 ROUT2 RIN2 RIN1 PORT 1 LINE INTERFACE DOUT2 ROUT2 PORT 2A/2B LINE INTERFACE RIN2 CH2 SELECT LINE 2A SELECT LINE 2A LTC2871 SELECT LINE 2B CH2 DIN2 ROUT2 DIN1 PORT 3 LOGIC INTERFACE ROUT1 DIN2 CH2 SELECT LINE 2B DOUT1 ROUT1 DOUT2 RIN2 DIN2 PORT 2B LINE INTERFACE PORT 2B LOGIC INTERFACE PORT 3 LINE INTERFACE PORT 3 LOGIC INTERFACE DOUT1 RIN1 LTC2871 CH2 ROUT2 DIN1 ROUT1 28701 F44 DOUT2 RIN2 DOUT1 RIN1 PORT 3 LINE INTERFACE 28701 F45 Figure 44. RS232 Triple Transceiver with Selectable Line Interface Figure 45. RS232 Triple Transceiver with Selectable Logic Interface LTC2870/ LTC2871 SELECT H/F INPUT2 INPUT1 Y RS485 INTERFACE Z RA, RO INPUT1 A B INPUT2 28701 F46 Figure 46. RS485 Receiver with Multiplexed Inputs 28701f 30 LTC2870/LTC2871 TYPICAL APPLICATIONS 3V TO 5.5V 220nF 10μH 2.2μF 1.7V TO VCC VCC SW 220nF CAP CAP VCC SW LTC2870 LTC2871 H/F H/F 2.2μF 0.1μF TE485 TE485 RS485 INTERFACE Y DI 120Ω RO 485/232 Y Z Z A A RA 120Ω B DIN1 DY 120Ω 120Ω B DOUT1 ROUT1 RIN1 DIN2 1μF 1.7V TO VCC VL VL 0.1μF 3V TO 5.5V 10μH RS232 INTERFACE DOUT2 ROUT2 RIN2 VDD GND VDD VEE 1μF VEE GND 28701 F47 1μF 1μF Figure 47. Typical Supply Connections with External Components Shown 3V TO 5.5V 470nF 22μH 2.2μF VCC VL GND CAP SW CAP LTC2870/ LTC2871 VDD VCC LTC2870/ LTC2871 VEE VEE VDD VL SW GND 28701 F48 2.2μF 2.2μF INDUCTOR: TAIYO YUDEN CBC2518T220M, MURATA LQH32CN220K53 Figure 48. Running Two LTC2870 or LTC2871 Devices from One Shared Power Source 28701f 31 LTC2870/LTC2871 PACKAGE DESCRIPTION FE Package 28-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1663) Exposed Pad Variation EB 9.60 – 9.80* (.378 – .386) 4.75 (.187) 4.75 (.187) 28 2726 25 24 23 22 21 20 19 18 1716 15 6.60 ±0.10 2.74 (.108) 4.50 ±0.10 SEE NOTE 4 0.45 ±0.05 EXPOSED PAD HEAT SINK ON BOTTOM OF PACKAGE 6.40 2.74 (.252) (.108) BSC 1.05 ±0.10 0.65 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.25 REF 1.20 (.047) MAX 0° – 8° 0.65 (.0256) BSC 0.195 – 0.30 (.0077 – .0118) TYP 0.05 – 0.15 (.002 – .006) FE28 (EB) TSSOP 0204 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 28701f 32 LTC2870/LTC2871 PACKAGE DESCRIPTION FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev A) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 2.74 REF 4.50 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN MILLIMETERS (INCHES) 3. DRAWING NOT TO SCALE 1 0.25 REF 19 1.20 (.047) MAX 0o – 8o 0.50 (.0196) BSC 0.17 – 0.27 (.0067 – .0106) TYP 0.05 – 0.15 (.002 – .006) FE38 (AA) TSSOP 0608 REV A 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE 28701f 33 LTC2870/LTC2871 PACKAGE DESCRIPTION UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 ±0.05 4.50 ± 0.05 3.10 ± 0.05 2.50 REF 2.65 ± 0.05 3.65 ± 0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 3.50 REF 4.10 ± 0.05 5.50 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ± 0.10 (2 SIDES) 0.75 ± 0.05 R = 0.05 TYP PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER 2.50 REF R = 0.115 TYP 27 28 0.40 ± 0.10 PIN 1 TOP MARK (NOTE 6) 1 2 5.00 ± 0.10 (2 SIDES) 3.50 REF 3.65 ± 0.10 2.65 ± 0.10 (UFD28) QFN 0506 REV B 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WXXX-X). 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 28701f 34 LTC2870/LTC2871 PACKAGE DESCRIPTION UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701 Rev C) 0.70 p 0.05 5.50 p 0.05 5.15 ± 0.05 4.10 p 0.05 3.00 REF 3.15 ± 0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 5.5 REF 6.10 p 0.05 7.50 p 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 p 0.10 0.75 p 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 s 45o CHAMFER 3.00 REF 37 0.00 – 0.05 38 0.40 p0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 7.00 p 0.10 5.50 REF 3.15 ± 0.10 (UH) QFN REF C 1107 0.200 REF 0.25 p 0.05 0.50 BSC R = 0.125 TYP R = 0.10 TYP BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 28701f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 35 LTC2870/LTC2871 TYPICAL APPLICATION Quad RS232 Transceiver with RS485 Communication Over Half-Duplex, Terminated Bus 3V TO 5.5V 470nF 22μH 2.2μF VCC VL CAP SW CAP VCC LTC2871 T1IN TE485 DOUT1 DIN1 RIN1 ROUT1 DOUT2 DIN2 RIN2 ROUT2 VL LTC2804 SW T1OUT1 ROUT1 RIN1 T2IN T2OUT ROUT2 VEE RIN2 VDD GND RO 120Ω B DI GND 3.3V A VDD LTC2854 Y A 120Ω Z B VCC 0.1μF TE DI 120Ω RO VEE GND 2.2μF 2.2μF 28701 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1334 Single 5V RS232/RS485 Multiprotocol Transceiver Dual Port, Single 5V Supply, Configurable, 10kV ESD LTC1387 Single 5V RS232/RS485 Multiprotocol Transceiver Single Port, Configurable LTC2801/LTC2802/ LTC2803/LTC2804 1.8V to 5.5V RS232 Single and Dual Transceivers Up to 1Mbps, 10kV ESD, Logic Supply Pin, Tiny DFN Packages LTC2854/LTC2855 3.3V 20Mbps RS485 Transceiver with Integrated Switchable Termination 3.3V Supply, Integrated, Switchable, 120Ω Termination Resistor, 25kV ESD LTC2859/LTC2861 20Mbps RS485 Transceiver with Integrated Switchable Termination 5V Supply, Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD LTM2881 Complete Isolated RS485/RS422 μModule Transceiver + Power 20Mbps, 2500VRMS Isolation with Integrated DC/DC Converter, Integrated, Switchable, 120Ω Termination Resistor, 15kV ESD LTM2882 Dual Isolated RS232 μModule Transceiver + Power 1Mbps, 2500VRMS Isolation with Integrated DC/DC Converter, ±10kV ESD 28701f 36 Linear Technology Corporation LT 1210 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2010