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STC485E
15kV ESD-Protected,Slew-Rate-Limited, Fail-Safe,True RS-485 Transceivers
General Description
The STC485E is 15kV electrostatic discharge (ESD)-protected, high-speed transceivers for RS-485 communication that contains one driver and one receiver. These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open, shorted or idle. This means that the receiver output will be a logic high if all transmitters on a terminated bus are disabled (high impedance). The STC485E features reduced slew-rate driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps. All devices feature enhanced ESD protection. All transmitter outputs and receiver inputs are protected to 15kV using the Human Body Model. These transceivers typically draw 400 of supply current when unloaded, or when fully loaded with the drivers disabled. A All devices have a 1/8-unit-load receiver input impedance that allows up to 256 transceivers on the bus. The STC485E is intended for half -duplex communications.
Applications
RS-485 Transceivers Level Translators Transceivers for EMI-Sensitive Applications Industrial-Control Local Area Networks
Features
ESD Protection for RS-485 I/O Pins 15kV-- Human Body Model 15kV-- IEC 1000-4-2, Air-Gap Discharge True Fail-Safe Receiver While Maintaining EIA/TIA-485 Compatibility Enhanced Slew-Rate Limiting Facilitates Error-Free Data Transmission 2nA Low-Current Shutdown Mode - to +12V Common-Mode Input Voltage Range 7V Allows up to 256 Transceivers on the Bus Thermal Shutdown Current-Limiting for Driver Overload Protection
Ordering Information
PART STC485EESA STC485EEPA TEMP. RANGE -40 to +85 C C -40 to +85 C C PIN-PACKAGE 8 SO 8 Plastic DIP
Selector Guide
PART NUMBER STC485E GUARANTEED DATA RATE (Mbps) 0.5 Low- Power SLEW-RATE Shutdown Yes LIMITED Yes DRIVER/ RECEIVER ENABLE Yes SHUTDOWN CURRENT (nA) 2 Transceivers On Bus 256 15kV ESD PROTECTION Yes PIN COUNT 8
Absolute Maximum Ratings
Supply Voltage (VCC) ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 7V Control Input Voltage (/RE, DE) ... ... ... ... ... ... -0.3V to (VCC + 0.3V) Driver Input Voltage (DI) ... ... ... ... ... ... ... ... ... -0.3V to (VCC + 0.3V) Driver Output Voltage (A, B) ... ... ... ... ... ... ... ... ... ... ... -7.5V to 12.5V Receiver Input Voltage (A, B) ... ... ... ... ... ... ... ... ... ... ... -7.5V to 12.5V Receiver Output Voltage (RO) ... ... ... ... ... ... ... -0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70 C) 8-Pin Plastic DIP (derate 9.09mW/ above +70 ... ... ... 727mW C C... 8-Pin SO (derate 5.88mW/ above +70 ... ... ... ... ... ... ... 471mW C ... Operating Temperature Ranges STC485EE_ _ ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... -40 to +85 C C Storage Temperature Range... ... ... ... ... ... ... ... ... ... -65 to +160 C C Lead Temperature (soldering, 10sec) ... ... ... ... ... ... ... ... ... ... +300 C
Stresses beyond those listed under " Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC Electrical Characteristics
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25 (Note 1) C.)
PARAMETER DRIVER Differential Driver Output (No Load) Differential Driver Output Change in Magnitude of Driver Differential Output Voltage (Note 2) Driver Common-Mode Output Voltage Change in Magnitude of Common -Mode Output Voltage (Note 2) Input High Voltage Input Low Voltage SYMBOL VOD1 VOD2 ? VOD VOC ? VOC VIH VIL CONDITIONS Figure 2 R= 50O, Figure 2 R= 50O? Figure 2 , R= 50O, Figure 2 R= 50O, Figure 2 DE, DI, /RE DE, DI, /RE 2.0 0.8 MIN TYP MAX UNITS 5 1.5 0.2 3 0.2 V V V V V V V
DI Input Hysteresis
Input Current (A, B) Driver Short-Circuit Output Current (Note
VHYS
IIN2 IOSD
UM3085E
DE = 0V, VCC = 0V or 5V VOUT = -7V VOUT = 12V -7V=VCM=12V VCM = 0V IOUT = -1.5mA, VID = 200mV IOUT = 2.5mA, VID = 200mV VCC = 5V, 0V=VOUT\=VCC -7V=VCM=12V 0V=VRO=VCC VIN = 12V VIN = -7V
100
1.0 -0.8 -250 250 -0.2 25 VCC - 1.5 0.4 1 96 8 -0.05
mV
mA mA
3)
RECEIVER Receiver Differential Threshold Voltage Receiver Input Hysteresis Receiver Output High Voltage Receiver Output Low Voltage Three-State (High Impedance) Output Current at Receiver Receiver Input Resistance Receiver Short-Circuit Output Current SUPPLY CURRENT Supply Current Supply Current in Shutdown Mode
VTH ? VTH VOH VOL IOZR RIN IOSR
V mV V V A kO? mA
60
ICC ISHDN
DE = VCC, /RE = 0V 0.3 or VCC DE = 0V, /RE = 0V 0.25 DE = 0V, /RE = VCC, DI = VCC or 0V 0.002 No load, DI = 0V or VCC
mA 10 A
ESD Protection for A, B
Human Body Model IEC 1000-4-2 Air Discharge
15 15
kV
Note 1: All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device ground unless otherwise noted. Note 2: VOD and VOC are the changes in VOD and VOC, respectively, when the DI input changes state. Note 3: Maximum current level applies to peak current just prior to foldback-current limiting; minimum current level applies during current limiting.
Switching Characteristics
(VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25 (Note 1) C.)
PARAMETER
SYMBOL tDPLH tDPHL tDSKEW tDR, tDF fMAX tDZH tDZL tDLZ tDHZ tRPLH, tRPHL tRSKD tRZL tRZH tRLZ tRHZ tSHDN tDZH(SHDN) tDZL(SHDN) tRZH(SHDN) tRZL(SHDN)
CONDITIONS Figures 4 and 6, RDIFF = 54? , CL1 = CL2 = 100pF Figures 4 and 6, RDIFF = 54? , CL1 = CL2 = 100pF Figures 4 and 6, RDIFF = 54? , CL1 = CL2 = 100pF Figures 5 and 7, CL = 100pF, S2 closed Figures 5 and 7, CL = 100pF, S1 closed Figures 5 and 7, CL = 15pF, S1 closed Figures 5 and 7, CL = 15pF, S2 closed Figures 11 and 13; | VID | =? .0V; 2 rise and fall time of VID =? 5ns 1 Figures 8 and 10; | VID | =? .0V; 2 rise and fall time of VID =? 5ns 1 Figures 3 and 9, CL = 100pF, S1 closed Figures 3 and 9, CL = 100pF, S2 closed Figures 3 and 9, CL = 100pF, S1 closed Figures 3 and 9, CL = 100pF, S2 closed (Note 4) Figures 5 and 7, CL = 15pF, S2 closed Figures 5 and 7, CL = 15pF, S1 closed Figures 3 and 9, CL = 100pF, S2 closed Figures 3 and 9, CL = 100pF, S1 closed
MIN 250 250
TYP 720 720 -3
MAX UNITS 1000 1000 100 750 500 2500 2500 100 100 ns ns ns kbps ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
Driver Input-to-Output Driver Output Skew | tDPLH - tDPHL | Driver Rise or Fall Time Maximum Data Rate Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output
200
530
127 3 3 20 20 20 20 50 200
200 30 50 50 50 50 600 4500 4500 3500 3500
| tRPLH - tRPHL | Differential Receiver Skew Receiver Enable to Output Low Receiver Enable to Output High
Receiver Disable Time from Low Receiver Disable Time from High Time to Shutdown Driver Enable from Shutdown-to-Output High Driver Enable from Shutdown-to-Output Low Receiver Enable from Shutdown-to-Output High Receiver Enable from Shutdown-to-Output Low
Typical Operating Characteristics
(VCC = +5V, TA = +25 unless otherwise noted.) C, NO-LOAD SUPPLYCURRENT(uA) NO-LOAD SUPPLY CURRENT vs.TEMPERATURE 60 OUTPUT CURRENT(mA) 50 40 30 20 10 0 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c) SHUTDOWN CURRENT vs.TEMPERATURE 20 18 16 14 12 10 8 6 4 2 0 SHUTDOWN(c) CURRENT nA OUTPUT LOW VOLTAGE V (c) 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c) 0 1 2 3 4 5 OUTPUT LOW VOLTAGE V (c) OUTPUT CURRENT OUTPUT CURRENT vs.RECEIVER OUTPUT LOW VOLTAGE vs.RECEIVER OUTPUT HIGH VOLTAGE 30 OUTPUT CURRENT(mA) 25 20 15 10 5 0 0 1 2 3 4 5 OUTPUT HIGH VOLTAGE V (c)
525 500 475 450 425 400 375 350 325 300
RECEIVER OUTPUT LOW VOLTAGE RECEIVER OUTPUT HIGH VOLTAGE vs.TEMPERATURE vs.TEMPERATURE 4.5 OUTPUT VOLTAGE V (c) PROPAGATION s(c) u DELAY 4.4 4.3 4.2 4.1 4.0 3.9 3.8 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c)
-60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c)
PROPAGATION s(c) n DELAY
PROPAGATION s(c) n DELAY
RECEIVER PROPAGATION DELAY DRIVER PROPAGATION DELAY RECEIVER PROPAGATION DELAY 5 00kbps MODE (c) v s.TEMPERATURE b ps MODE 1 15k (c) v s.TEMPERATURE bps MODE 1 0M (c) v s.TEMPERATURE 140 112 2.20 110 2.15 135 108 130 125 120 115 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c) 106 104 102 100 98 96 94 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c) 2.10 2.05 2.00 1.95 1.90 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c)
Typical Operating Characteristics(continued)
(VCC = +5V, TA = +25 unless otherwise noted.) C, DRIVER PROPAGATION DELAY DRIVER DIFFERENTIAL OUTPUT VOLTAGE DRIVER PROPAGATION DELAY 1 0Mbps MODE (c) v s.TEMPERATURE vs.TEMPERATURE 5 00kbps MODE TEMPERATURE (c) v s. 920 60 1.90 880 55 1.89 840 50 800 1.88 45 760 1.87 720 40 1.86 680 35 640 1.85 30 600 1.84 25 560 20 520 1.83 -60 -40 -20 0 20 40 60 80 100 -60 -40 -20 0 20 40 60 80 100 -60 -40 -20 0 20 40 60 80 100 TEMPERATURE ae (c) TEMPERATURE ae (c) TEMPERATURE ae (c) PROPAGATION s(c) n DELAY OUTPUT CURRENT vs. DRIVER OUTPUT CURRENT OUTPUT CURRENT vs. vs.DIFFERENTIAL OUTPUT VOLTAGE DRIVER OUTPUT LOW VOLTAGE DRIVER OUTPUT HIGH VOLTAGE 100 140 -100 -90 120 -80 10 100 -70 -60 80 1 -50 60 -40 -30 40 0.1 -20 20 -10 0 0.01 0 0 1 2 3 4 5 0 2 4 6 8 10 12 -8 -6 -4 -2 02 46 OUTPUT LOW VOLTAGE V (c) DIFFERENTIAL OUTPUTV (c) VOLTAGE OUTPUT HIGH VOLTAGE V (c) OUTPUT CURRENT (c) mA OUTPUT CURRENT (c) mA OUTPUT VOLTAGE V (c)
OUTPUT CURRENT (c) mA
PROPAGATION s(c) n DELAY
Typical Operating Characteristics(continued)
(VCC = +5V, TA = +25 unless otherwise noted.) C, RECEIVER PROPAGATION DELAY DRIVER PROPAGATION DELAY
DI VA VB 2V/div
5V/div
VY VZ RO 5V/div
2.5V/div
50ns/div
50ns/div
Pin Description
PIN NAME RO /RE FUNCTION Receiver Output. If A > B by -50mV, RO will be high; if A < B by 200mV, RO will be low. Receiver Output Enable. RO is enabled when /RE is low; RO is high impedance when /RE is high. If /RE is high and DE is low, the device will enter a low-power shutdown mode. Driver Output Enable. The driver outputs are enabled by bringing DE high. They are high impedance when DE is low. If /RE is high and DE is low, the device will enter a low-power shutdown mode. If the driver outputs are enabled, the parts function as line drivers. While they are high impedance, they function as line receivers if /RE is low. Driver Input. A low on DI forces output A low and output B high. Similarly, a high on DI forces output A high and output B low. Ground Noninverting Receiver Input and Noninverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply: VCC=5V 5%
1 2
3
DE
4 5 6 7 8
DI GND A B VCC
Function Tables
Table 1. Transmitting
INPUTS /RE X X DE DI OUTPUTS B A MODE
/RE
Table 2. Receiving
INPUTS DE X X X 0 A, B =?0.05V =?0.2V Inputs Open X OUTPUTS MODE RO 0 0
0 1
1 1 0 0
1 0
X X
0 1
High-Z High-Z
1 0
High-Z High-Z
Normal Normal Normal Shutdown
0 1
1 0 1
High-Z
Normal Normal Normal Shutdown
X = Don' care; High-Z = High impedance t
X = Don' care; High-Z = High impedance t
TOP VIEW STC485E RO1 RE2 DE3 DI 4 R 8 7 6 5 Vcc B A GND 1 RO 2 RE 3 DE 4 DI R 8 0.1uF Rt B A D Vcc 7B Rt 6A 5 GND DE DI
D DIP/SO
D
R RE
RO
Figure 1. STC485E / Pin Configuration and Typical Operating Circuit
Detailed Description
The STC485E high-speed transceivers for RS-485 communication contain one driver and one receiver. These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled (see the Fail-Safe section). The STC485E feature reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps (see the Reduced EMI and Reflections section). All of these parts operate from a single +5V supply. Drivers are output short-circuit current limited. Thermal shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal shutdown circuitry places the driver outputs into a high impedance state.
Fail-Safe
The STC485E guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the receiver threshold between - mV and -200mV. If 50 the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is logic high. If A-B is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the receiver' differential input voltage is pulled to 0V s by the termination. With the receiver thresholds of the STC485E, , this results in a logic high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold complies with the 200 mV EIA/TIA-485 standard.
15kV ESD Protection
As with all STC devices, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver outputs and receiver inputs of the STC485E have extra protection against static electricity. Union' engineers have developed state-of-the-art structures to protect these pins s against ESD of 15kV without damage. The ESD-protected pins are tested with reference to the ground pin in a powered-down condition. They are tested to 15kV using the Human Body Model.
ESD Test Conditions
ESD performance depends on a variety of conditions. Contact Union for a reliability report that documents test setup, test methodology, and test results.
Human Body Model
Figure 11a shows the Human Body Model and Figure 11b shows the current waveform it generates when discharged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of interest which is then discharged into the test device through a 1.5k? resistor. ?
Machine Model
The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. The objective is to emulate the stress caused when I/O pins are contacted by handling equipment during test and assembly. All pins require this protecduring test and assembly. All pins require this protection, not just RS-485 inputs and outputs.
Applications Information
256 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12kO?(one-unit load), and the standard driver can drive up to 32 unit loads. The STC family of trans -ceivers have a 1/8-unit-load receiver input impe -dance (96kO), allowing up to 256 transceivers to be connected in parallel on one communication line. Any combination of these devices and/or other RS-485 transceivers with a total of 32 unit loads or less can be connected to the line.
Reduced EMI and Reflections
The STC485E is slew-rate limited, minimizing EMI and reducing reflections caused by improperly terminated cables. Figure 12 shows the same signal displayed for a STC485E, transmitting under the same conditions. In general, a transmitter' rise time relates directly to the length of an unterminated stub, which can be driven with only minor s waveform reflections. The following equation expresses this relationship conservatively: Length = tRISE / (10 x 1.5ns/ft) where tRISE is the transmitter' rise time. s A system can work well with longer unterminated stubs, even with severe reflections, if the waveform settles out before the UART samples them.
Low-Power Shutdown Mode
Low-power shutdown mode is initiated by bringing both /RE high and DE low. In shutdown, the devices typically draw only 2 nA of supply current. /RE and DE may be driven simultaneously; the parts are guaranteed not to enter shutdown if /RE is high and DE is low for less than 50ns. If the inputs are in this state for at least 600ns, the parts are guaran -teed to enter shutdown. Enable times tZH and tZL in the Switching Characteristics tables assume the part was not in a low-power shutdown state. Enable times tZH(SHDN) and tZL(SHDN) assume the parts were shut down. It takes drivers and receivers longer to become enabled from low-power shutdown mode (tZH(SHDN), tZH(SHDN)) than from driver/receiver -disable mode (tZH, tZL).
Driver Output Protection
Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. The first, a foldback current limit on the output stage, provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics). The second, a thermal shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature becomes excessive.
Line Length vs. Data Rate
The RS-485/RS-422 standard covers line lengths up to 4000 feet. For line lengths greater than 4000 feet, repeater is required.
Typical Applications
The STC485E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figures 14 show typical network applications circuits. To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible.
Figure 2. Driver DC Test Load
Figure 3. Receiver Enable/Disable Timing Test Load
Figure 4. Driver Timing Test Circuit
Figure 5. Driver Enable and Disable Timing Test Load
Figure 6. Driver Propagation Delays
Figure 7. Driver Enable and Disable Times
Figure 8. Receiver Propagation Delays
Figure 9. Receiver Enable and Disable Times
Figure 10. Receiver Propagation Delay Test Circuit
RD 1500 | CHARGE-CURRENT DISCHARGE LIMIT RESISTORRESISTANCE HIGHC S STORAGE VOLTAGE 100pF CAPACITOR DC SOURCE
RC 1M |
DEVICE UNDER TEST
Figure 11a. Human Body ESD Test Model
Figure 11b. Human Body Current Waveform
Figure 12. Driver Output Waveform and FFT Plot of STC485E, Transmitting a 20kHz Signal 120 | DI D DE RO RE R R STC485E D RE DE RO A B A B
Figure 13. STC485E System Differential Voltage at 50kHz Driving 4000ft of Cable 120 | B D DI B A A R R D RO RE
DE
DI Figure 16. Typical Half-Duplex RS-485 Network
DI
RE DE RO
Package Information ES M E D I M MIIN C HA XMIIL L I M X T E R S NM NMA A 0 . 0 5 30 . 0 6 91 . 3 5 1 . 7 5 A 1 0 . 0 0 40 . 0 1 00 . 1 0 0 . 2 5 0a - 8a B 0 . 0 1 40 . 0 1 90 . 3 5 0 . 4 9 C 0 . 0 0 70 . 0 1 00 . 1 9 0 . 2 5 E 0 . 1 5 00 . 1 5 73 . 8 0 4 . 0 0 e 0.050 1.27 H 0 . 2 2 80 . 2 4 45 . 8 0 6 . 2 0 L 0 . 0 1 60 . 0 5 00 . 4 0 1 . 2 7
D A1 A e B 0.101mm 0.004in. C
L
M DIM PINS INCHES ILLIMETERS MINMAX MINMAX SO 0.197 4.80 5.00 SMALL OUTLINE D 8 0.189 D 14 0.337 0.344 8.55 8.75 PACKAGE D 16 0.386 0.394 9.8010.00 0 .150in. (c) 21-0041A
E
H
D A A2 L A1 e D1 B1 B A3
E E1
0a a - 15 eA eB C
Plastic DIP PLASTIC DUAL-IN-LINE PACKAGE (0.300in.)
INCHES ILLIMETERS M DIM MIN MAXMINMAX A - 0.200 - 5.08 A1 0.015 - 0.38 A2 0.125 0.1753.18 4.45 A3 0.055 0.0801.40 2.03 B 0.016 0.0220.41 0.56 B1 0.045 0.0651.14 1.65 C 0.008 0.0120.20 0.30 D1 0.005 0.0800.13 2.03 E 0.300 0.3257.62 8.26 E1 0.240 0.3106.10 7.87 e 0.100 - 2.54 eA 0.300 - 7.62 eB - 0.400 - 10.16 L 0.115 0.1502.92 3.81 DIM PIN INCHES MILLIMETERS MINMAX MINMAX D8 0.348 0.390 8.849.91 D 14 0.735 0.765 8.67 9.43 11 D 16 0.745 0.765 8.92 9.43 11 D 18 0.885 0.915 22.48 3.24 2 D 20 1.015 1.045 25.78 6.54 2 D 24 1.14 1.265 28.96 2.13 3

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