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19-4098; Rev 0; 5/08
80V Fault-Protected Full-Duplex RS-485 Transceiver
General Description
The MAX13448E full-duplex RS-485 transceiver features inputs and outputs fault protected up to 80V (with respect to ground). The device operates from a +3.0V to +5.5V supply and features true fail-safe circuitry, guaranteeing a logic-high receiver output when the receiver inputs are open or shorted. This enables all receiver outputs on a terminated bus to output logichigh when all transmitters are disabled. The MAX13448E features a slew-rate limited driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission at data rates up to 500kbps with a +5V supply, and 250kbps with a +3.3V supply. The MAX13448E includes a hot-swap capability to eliminate false transitions on the bus during power-up or hot insertion. The driver and receiver feature active-high and active-low enables, respectively, that can be connected together externally to serve as a direction control. The MAX13448E features an 1/8-unit load receiver input impedance, allowing up to 256 transceivers on the bus. All driver outputs are protected to 8kV ESD using the Human Body Model. The MAX13448E is available in a 14-pin SO package and operates over the extended -40C to +85C temperature range. o True Fail-Safe Receiver o Hot-Swap Input Structure on DE o ESD Protection on the RS-485 I/O Ports 8kV Human Body Model o Slew-Rate Limiting Facilitates Error-Free Data Transmission o 1/8-Unit Load Allows Up to 256 Transceivers on the Bus o -7V to +12V Common-Mode Input Voltage Range o +3.0V to +5.5V Operating Supply Voltage o Available in 14-Pin SO Package
Features
o 80V Fault Protection on the RS-485 I/O Ports
MAX13448E
Ordering Information
PART MAX13448EESD+ TEMP RANGE -40C to +85C PIN-PACKAGE 14 SO
+Denotes a lead-free package.
Applications
Industrial Control Systems HVAC Control systems Utility Meters Motor Driver Control Systems
Pin Configuration appears at end of data sheet.
Functional Diagram
+ R
N.C. 1 RO 2 RE 3 DE 4 DI 5
14 VCC 13 N.C. 12 A 11 B 10 Z D
MAX13448E
DE 4 14
VCC 1F 9 Y Rt Z VCC
RE
DI
5
D
10
R
RO
12 RO 2 1, 8, 13 3 RE 6, 7 GND R 11
A Rt B D DI
GND 6 GND 7
9Y N.C. 8 N.C.
GND
DE
SO
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
ABSOLUTE MAXIMUM RATINGS
(All voltages reference to GND.) Supply Voltage (VCC).............................................................+6V Control Input Voltage (RE, DE)...................-0.3V to (VCC + 0.3V) Driver Input Voltage (DI).............................-0.3V to (VCC + 0.3V) Receiver Input Voltage (A, B (Note 1)) ................................80V Driver Output Voltage (Y, Z (Note 1)) ..................................80V Receiver Output Voltage (RO)....................-0.3V to (VCC + 0.3V) Short-Circuit Duration (RO, A, B) ...............................Continuous Continuous Power Dissipation (TA = +70C) 14-Pin SO (derate 8.3mW/C above +70C)................667mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: If the RS-485 transmission lines are unterminated and a short to a voltage VSHT occurs at a remote point on the line, an active local driver (with DI switching) may see higher voltage than VSHT due to inductive kickback at the driver. Terminating the line with a resistor equal to its characteristic impedance minimizes this kickback effect.
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.
ELECTRICAL CHARACTERISTICS
(VCC = +3.0 to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Notes 2, 3)
PARAMETER VCC Supply Voltage Range Supply Current Supply Current in Shutdown Mode Supply Current with Output Shorted to 60V DRIVER Differential Driver Output Change in Magnitude of Differential Output Voltage Driver Common-Mode Output Voltage Change in Magnitude of Common-Mode Voltage Driver Short-Circuit Output Current Driver Short-Circuit Foldback Output Current Driver-Limit Short-Circuit Foldback Output Current Driver Input High Voltage Driver Input Low Voltage Driver Input Current VOD VOD VOC VOC IOSD IOSDF IOSDL VDIH VDIL IDIN -1 RL = 100, Figure 1 RL = 54, Figure 1 RL = 100 or 54, Figure 1 (Note 4) RL = 100 or 54, Figure 1 RL = 100 or 54, Figure 1 (Note 4) DI = low, 0V VY or VZ +12V DI = high, -7V VY or VZ VCC (Note 5) DI = low, (VCC - 1V) VY or VZ +12V DI = high, -7V VY or VZ +1V VY or VZ + 22V, RL = 100 VY or VZ -13V, RL = 100 -6 2 0.8 +1 -250 +10 -10 +6 -0.2 2 1.5 -0.2 VCC/2 VCC VCC 0.2 3 +0.2 +250 V V V V mA mA mA V V A SYMBOL VCC IQ ISHDN ISHRT No load, DE, DI, RE = 0V or VCC, VCC = 3.3V No load, DE, DI, RE = 0V or VCC, VCC = 5V DE = GND, RE = VCC, VCC = 3.3V DE = GND, RE = VCC, VCC = 5V DE = GND, RE = GND, short to +60V DE = GND, RE = GND, short to -60V CONDITION MIN 3.0 TYP MAX 5.5 15 15 100 100 15 15 UNITS V mA A mA
2
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80V Fault-Protected Full-Duplex RS-485 Transceiver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0 to +5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Notes 2, 3)
PARAMETER RECEIVER VA, VB = +12V Input Current IA , B VA, VB = -7V VA, VB = 80V Receiver Differential Threshold Voltage Receiver Input Hysteresis Output High Voltage Output Low Voltage Three-State Output Current at Receiver Receiver Output Short-Circuit Current ESD PROTECTION All Pins ESD Protection Level (A and B, Y and Z) CONTROL Control Input High Voltage Control Input Low Voltage Input Current Latch During First Rising Edge PROTECTION SPECIFICATIONS Overvoltage Protection A, B, Y, Z -80 +80 V VCIH VCIL IIN DE, RE DE, RE DE, RE 80 2 0.8 V V A Human Body Model Human Body Model 2 8 kV kV VTH VTH VOH VOL IOZR IOSR IOH = -1.6mA IOL = 1mA 0 VA, VB VCC 0 VRO VCC -1 -95 VCC 0.6 0.4 +1 +95 -7V VCM +12V VCC = GND or VCC = +3.0V to +5.5V -100 -6 -200 25 +6 -50 +125 A A mA mV mV V V A mA SYMBOL CONDITION MIN TYP MAX UNITS
MAX13448E
SWITCHING CHARACTERISTICS (VCC = +3.3V 10%)
(TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.)
PARAMETER DRIVER Driver Differential Propagation Delay Driver Differential Output Transition Time Differential Driver Output Skew Maximum Data Rate Driver Enable Time to Output High tDPLH, tDPHL tLH, tHL tDSKEW fMAX tDZH RL = 500, CL = 50pF, Figure 4 RL = 54, CL = 50pF, Figures 2 and 3 RL = 54, CL = 50pF, Figures 2 and 3 RL = 54, CL = 50pF, tDSKEW = [tDPLH tDPHL], Figures 2 and 3 250 2000 250 150 700 1500 1200 200 ns ns ns kbps ns SYMBOL CONDITION MIN TYP MAX UNITS
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
SWITCHING CHARACTERISTICS (VCC = +3.3V 10%) (continued)
(TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.)
PARAMETER Driver Disable Time from Output High Driver Enable Time from Shutdown to Output High Driver Enable Time to Output Low Driver Disable Time from Output Low Driver Enable Time from Shutdown to Output Low Driver Time to Shutdown RECEIVER Receiver Propagation Delay Receiver Output Skew Receiver Enable Time to Output High Receiver Disable Time from Output High Receiver Wake Time from Shutdown Receiver Enable Time to Output Low Receiver Disable Time from Output Low Receiver Time to Shutdown tRPLH, tRPHL tRSKEW tRZH tRHZ tRWAKE tRZL tRLZ tSHDN CL = 20pF, VID = 2V, VCM = 0V, Figure 6 CL = 20pF, tRSKEW = [tRPLH - tRPHL], Figure 6 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 500, CL = 50pF 2000 200 1000 150 5 1000 150 200 ns ns ns ns s ns ns ns SYMBOL tDHZ CONDITION RL = 500, CL = 50pF, Figure 4 MIN TYP MAX 1000 8 1500 2000 8 12 UNITS ns s ns ns s s
tDZH(SHDN) RL = 500, CL = 50pF, Figure 4 tDZL tDLZ RL = 500, CL = 50pF, Figure 5 RL = 500, CL = 50pF, Figure 5
tDZL(SHDN) RL = 500, CL = 50pF, Figure 5 tSHDN RL = 500, CL = 50pF
SWITCHING CHARACTERISTICS (VCC = +5V 10%)
(TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER DRIVER Driver Differential Propagation Delay Driver Differential Output Transition Time Differential Driver Output Skew Maximum Data Rate tDPLH, tDPHL tLH, tHL tDSKEW fMAX RL = 54, CL = 50pF, Figure 3 RL = 54, CL = 50pF, Figure 3 RL = 54, CL = 50pF, tDSKEW = [tDPLH tDPHL], Figure 3 500 100 800 1200 200 ns ns ns kbps SYMBOL CONDITION MIN TYP MAX UNITS
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80V Fault-Protected Full-Duplex RS-485 Transceiver
SWITCHING CHARACTERISTICS (VCC = +5V 10%) (continued)
(TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.)
PARAMETER Driver Enable Time to Output High Driver Disable Time from Output High Driver Enable Time from Shutdown to Output High Driver Enable Time to Output Low Driver Disable Time from Output Low Driver Enable Time from Shutdown to Output Low Driver Time to Shutdown RECEIVER Receiver Propagation Delay Receiver Output Skew Receiver Enable Time to Output High Receiver Disable Time from Output High Receiver Wake Time from Shutdown Receiver Enable Time to Output Low Receiver Disable Time from Output Low Receiver Time to Shutdown tRPLH, tRPHL tRSKEW tRZH tRHZ tRWAKE tRZL tRLZ tSHDN CL = 20pF, VID = 2V, VCM = 0V, Figure 6 CL = 20pF, tRSKEW = [tRPLH - tRPHL], Figure 6 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 1k, CL = 20pF, Figure 7 RL = 500, CL = 50pF 2000 200 1000 150 8 1000 150 150 ns ns ns ns s ns ns ns SYMBOL tDZH tDHZ CONDITION RL = 500, CL = 50pF, Figure 4 RL = 500, CL = 50pF, Figure 4 MIN TYP MAX 1500 1000 8 1000 2 8 12 UNITS ns ns s ns s s s
MAX13448E
tDZH(SHDN) RL = 500, CL = 50pF, Figure 4 tDZL tDLZ RL = 500, CL = 50pF, Figure 5 RL = 500, CL = 50pF, Figure 5
tDZL(SHDN) RL = 500, CL = 50pF, Figure 5 tSHDN RL = 500, CL = 50pF
Note 2: Parameters are 100% production tested at TA = +25C, unless otherwise noted. Limits over temperature are guaranteed by design. Note 3: All currents into the device are positive. All currents out of the device are negative. All voltages are referenced to device ground, unless otherwise noted. Note 4: VOD and VOC are the changes in VOD and VOC, respectively, when the DI input changes state. Note 5: The short-circuit output current applies to peak current just prior to foldback current limiting. The short-circuit foldback output current applies during current limiting to allow a recover from bus contention.
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
Typical Operating Characteristics
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
RECEIVER OUTPUT SOURCE CURRENT vs. OUTPUT HIGH VOLTAGE
MAX13448E toc01 MAX13448E toc02
SUPPLY CURRENT vs. TEMPERATURE
4.20 DE = RE = LOW A - B = HIGH DI = FLOATING SUPPLY CURRENT (mA) 4.15 3.4 3.2 OUTPUT HIGH VOLTAGE (V) 3.0 2.8 2.6
RECEIVER OUTPUT SINK CURRENT vs. OUTPUT LOW VOLTAGE
0.8 OUTPUT LOW VOLTAGE (V) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 +25C 0 -40C +85C DE = RE = LOW B - A = HIGH
MAX13448E toc03
0.9
-40C
4.10
+25C 2.4 2.2 DE = RE = LOW A - B = HIGH 0 +85C
4.05 -40 -15 10 35 TEMPERATURE (C) 60 85
2.0 2 4 6 8 OUTPUT SOURCE CURRENT (mA) 10
0
2 4 6 8 OUTPUT SINK CURRENT (mA)
10
RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE
MAX13448E toc04
RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE
DE = RE = LOW B - A = HIGH ISINK = 1mA
MAX13448E toc05
3.25
0.075 0.070 OUTPUT LOW VOLTAGE (V) 0.065 0.060 0.055 0.050 0.045 0.040
OUTPUT HIGH VOLTAGE (V)
3.24
3.23
3.22
3.21
3.20 -40
DE = RE = LOW A - B = HIGH ISOURCE = 1mA -15 10 35 TEMPERATURE (C) 60 85
-40
-15
10 35 TEMPERATURE (C)
60
85
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. DIFFERENTIAL OUTPUT CURRENT
MAX13448E toc06
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX13448E toc07
3.5 DIFFERENTIAL OUTPUT VOLTAGE (V)
1.94 DIFFERENTIAL OUTPUT VOLTAGE (V)
3.0
1.92
2.5
1.90
2.0
1.5 DE = RE = HIGH DI = HIGH 1.0 0 20 40 60 80 DIFFERENTIAL OUTPUT CURRENT (mA) 100
1.88 DE = RE = HIGH DI = HIGH RLOAD = 54 1.86 -40 -15 10 35 TEMPERATURE (C) 60 85
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80V Fault-Protected Full-Duplex RS-485 Transceiver
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
SINGLE-ENDED DRIVER OUTPUT HIGH VOLTAGE vs. SOURCE CURRENT
DE = RE = HIGH DI = HIGH OUTPUT HIGH VOLTAGE (V) 3.30
MAX13448E toc08
MAX13448E
SINGLE-ENDED DRIVER SINK CURRENT vs. OUTPUT LOW VOLTAGE
DE = RE = HIGH DI = HIGH
MAX13448E toc09
SHUTDOWN CURRENT vs. TEMPERATURE
MAX13448E toc10
3.35
0.12 0.10 OUTPUT LOW VOLTAGE (V) 0.08 0.06 0.04 0.02 0
30 25 SHUTDOWN CURRENT (A) 20 15 10 5 0
3.25
3.20
3.15
3.10 0 2 4 6 8 OUTPUT SOURCE CURRENT (mA) 10
0
2 4 6 8 OUTPUT SINK CURRENT (mA)
10
-40
-15
10 35 TEMPERATURE (C)
60
85
DRIVER PROPAGATION DELAY (500kbsp)
MAX13448E toc11
RECEIVER PROPAGATION DELAY (500kbsp)
MAX13448E toc12
2V/div 1V/div
1V/div
2V/div
400ns
400ns
DRIVER PROPAGATION DELAY vs. TEMPERATURE
MAX13448E toc13
RECEIVER PROPAGATION DELAY vs. TEMPERATURE
DE = RE = LOW CLOAD = 20pF PROPAGATION DELAY (ns) 375
MAX13448E toc14
500 tDPLH PROPAGATION DELAY (ns) 450
400
400 tDPHL 350 DE = RE = HIGH RLOAD = 54 CLOAD = 50pF -40 -15 10 35 TEMPERATURE (C) 60 85
350
tRPLH
325
tRPHL
300
300 -40 -15 10 35 TEMPERATURE (C) 60 85
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
Pin Description
PIN 1, 8, 13 2 3 4 5 6, 7 9 10 11 12 14 NAME N.C. RO RE DE DI GND Y Z B A VCC FUNCTION No Connection. Not internally connected. Connect N.C. to GND or leave it unconnected. Receiver Output. If receiver is enabled and (A - B) -50mV, RO = high; if (A - B) -200mV, RO = low. Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high. Drive RE high and DE low to enter low-power shutdown mode. Driver Output Enable. Drive DE high to enable the driver outputs. Drive DE low to put the outputs in high impedance. Drive RE high and DE low to enter low-power shutdown mode. Driver Input. Drive DI low to force the noninverting output low and the inverting output high. Drive DI high to force the noninverting output high and the inverting output low. Ground Noninverting Driver Output Inverting Driver Output Inverting Receiver Input Noninverting Receiver Input Positive Supply. VCC = +3.0V to +5.5V. Bypass VCC to GND with a 1F ceramic capacitor as close to VCC as possible. Typical VCC values are at VCC = +3.3V and VCC = +5.0V.
Y DI RL/2 VOD RL/2 Z VOC
VCC VCC/2 0 tDPLH tDPHL 1/2 VO
Z VO Y 1/2 VO VO VOD 0 -VO VOD = V (Y) - V (Z) 10% tLH tSKEW = |tDPLH - tDPHL| 90% tHL 90% 10%
Figure 1. Driver DC Test Load
VCC DE CL Y DI Z VO RL CL
Figure 3. Driver Propagation Delays
Figure 2. Driver Timing Test Circuit
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
Y 0 OR VCC D1 D Z CL 50pF S1 OUT RL = 500
GENERATOR
50
VCC DE tDZH, tDZH(SHDN) VCC/2 0 0.25V OUT VOM = (0 + VOH)/2 tDHZ 0
VOH
Figure 4. Driver Enable and Disable Times (tDHZ, tDZH, tDZH(SHDN))
VCC RL = 500 S1 OUT Z CL 50pF
Y 0 OR VCC D1 D
GENERATOR
50
VCC DE tDZL, tDZL(SHDN) VCC/2 0
tDLZ VCC OUT VOL VOM = (VOL + VCC)/2 0.25V
Figure 5. Driver Enable and Disable Times (tDLZ, tDZL, tDZL(SHDN))
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
B
A VID B R
RO CL 20pF
A tRPHL VOH + VOL
2
tRPLH VOH
0
RO VOL
tSKEW = |tRPLH - tRPHL|
Figure 6. Receiver Propagation Delays
S1 +1.5V -1.5V B S3 A VID RO R RE CL 20pF 1k VCC
S2
GENERATOR
50
S1 OPEN S2 CLOSED S3 = +1.5V VCC
S1 CLOSED S2 OPEN S3 = -1.5V VCC VCC/2 RE
RE tRZH, tRWAKE* RO VOH/2
0
0 tRZL, tSHDN*
VOH
VCC (VOL + VCC)/2
0
RO
VOL
S1 OPEN S2 CLOSED S3 = +1.5V VCC/2 tRHZ, tSHDN*
VCC
S1 CLOSED S2 OPEN S3 = -1.5V VCC/2
VCC
RE
0
RE tRLZ, tSHDN*
0
VOH 0.25V RO 0 RO 0.25V
VCC *DE = LOW VOL
Figure 7. Receiver Enable and Disable Times
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
Detailed Description
The MAX13448E 80V fault-protected RS-485/RS-422 transceiver contains one driver and one receiver. This device features fail-safe circuitry, guaranteeing a logichigh receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled. The device has a hot-swap input structure that prevents disturbances on the differential signal lines when a circuit board is plugged into a hot backplane. All receiver inputs and driver outputs are protected to 8kV ESD using the Human Body Model. The MAX13448E features a reduced slew-rate driver that minimizes EMI and reduces reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps.
Table 1. Function Table
TRANSMITTING INPUT RE X X 0 1 DE 1 1 0 0 INPUT RE 0 0 1 1 DE X X 1 0 A-B -50mV -200mV X X DI 0 1 X X Z 1 0 High Impedance OUTPUT Y 0 1 High Impedance
High Impedance (Shutdown) OUTPUT RO 1 0 Disabled High Impedance (Shutdown)
RECEIVING
Driver
The driver accepts a single-ended, logic-level input (DI) and converts it to a differential, RS-485/RS-422 level output (A and B). Deasserting the driver enable places the driver outputs (A and B) into a high-impedance state.
X = Don't care; shutdown mode, driver, and receiver outputs are high impedance.
Receiver
The receiver accepts a differential, RS-485/RS-422 level input (A and B), and translates it to a singleended, logic-level output (RO). Deasserting the receiver enable places the receiver outputs (RO) into a high-impedance state (see Table 1).
Low-Power Shutdown
Low-power shutdown is initiated by bringing DE low and RE high. In shutdown, the device draws a maximum of 100A of supply current. The device is guaranteed to not enter shutdown if DE is low and RE is high for 1s. If the inputs are in this state for at least 1ms, the device is guaranteed to enter shutdown. In the shutdown state, the driver outputs (A and B) as well as the receiver output (RO) are in a highimpedance state.
80V Fault Protection
In certain applications, such as industrial control, driver outputs and receiver inputs of an RS-485 device sometimes experience common-mode voltages in excess of the -7V to +12V range specified in the EIA/TIA-485 standard. In these applications, ordinary RS-485 devices (typical absolute maximum ratings of -8V to +12.5V) may experience damage without the addition of external protection devices.
To reduce system complexity and the need for external protection, the driver outputs and receiver inputs of the MAX13448E withstand voltage faults of up to 80V with respect to ground without damage (see the Absolute Maximum Ratings section, Note 1). Protection is guaranteed regardless of whether the device is active, in shutdown, or without power. Certain parasitic effects present while driving an unterminated cable may cause the voltage seen at driver outputs to exceed the absolute maximum limit, while the DI input is switched during a 80V fault on the A or B input. Therefore, a termination resistor is recommend in order to maximize the overvoltage fault protection while the DI input is being switched. If the DI input does not change state while the fault voltage is present, the MAX13448E will withstand up the 80V on the RS-485 inputs, regardless of the presence of a termination resistor. While the MAX13448E is not damaged by up to 80V commonmode voltages, the RO, Y, and Z outputs will be in an indeterminate state if the common-mode voltage exceeds -7V to +12V.
True Fail-Safe
The MAX13448E 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
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11
80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
RC 1M CHARGE-CURRENTLIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1500 DISCHARGE RESISTANCE DEVICE UNDER TEST IP 100% 90% AMPS STORAGE CAPACITOR 36.8% 10% 0 0 tRL TIME tDL CURRENT WAVEFORM Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE)
Cs 100pF
Figure 8a. Human Body ESD Test Model
Figure 8b. Human Body Current Waveform
receiver threshold between -50mV and -200mV. If 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's differential input voltage is pulled to 0V by the termination. With the receiver thresholds of the MAX13448E, this results in a logic-high with a 50mV minimum noise margin. The -50mV to -200mV threshold complies with the 200mV EIA/TIA-485 standard.
100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5k resistor.
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 the Typical Operating Characteristics). The second, a thermal-shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature exceeds +160C (typ).
8kV ESD Protection
As with all Maxim 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 MAX13448E have extra protection against static electricity. Maxim's engineers have developed state-of-theart structures to protect these pins against ESD of 8kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the MAX13448E keeps working without latchup or damage. ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the MAX13448E are characterized for protection to the following limits: * 8kV using the Human Body Model
Hot-Swap Capability
Hot-Swap Inputs When circuit boards are inserted into a powered backplane, disturbances to the data bus can lead to data errors. Upon initial circuit-board insertion, the data communication processor undergoes its own power-up sequence. During this period, the processor's logicoutput drivers are high impedance and are unable to drive the DE input of the device to a defined logic level. Leakage currents up to 10A from the high-impedance state of the processor's logic drivers could cause standard CMOS enable inputs of a transceiver to drift to an incorrect logic level. Additionally, parasitic circuitboard capacitance could cause coupling of VCC or GND to the enable inputs. Without the hot-swap capability, these factors could improperly enable the transceiver's driver or receiver. When VCC rises, an internal pulldown circuit holds DE low. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hot-swap tolerable input.
ESD Test Conditions ESD performance depends on a variety of conditions. Contact Maxim for a reliability report that documents test setup, test methodology, and test results. Human Body Model Figure 8a shows the Human Body Model, and Figure 8b shows the current waveform it generates when discharged into a low impedance. This model consists of a
12
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80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
VCC 10s TIMER SR LATCH TIMER
MAX13448E is specified as 1/8 unit loads. This means a compliant transmitter can drive up to 256 MAX13448E devices. Reducing the common mode and/or changing the characteristic impedance of the cable changes the maximum number of receivers that can be used. Refer to the TIA/EIA-485 specification for further details.
Proper Termination and Cabling/Wiring Configurations
When the data rates for RS-485 are high relative to its cable lengths, the system is subject to proper transmission line design. In most cases, a single, controlledimpedance cable or trace should be used and should be properly terminated on both ends with the characteristic impedance of the cable/trace. RS-485 transceivers should be connected to the cable/traces with minimum length wires to prevent stubs. Star configurations and improperly terminated cables can cause data loss. Refer to the Applications section of the Maxim website or to TIA/EIA publication TSB89 for further information.
5k DE 100A 500A M1 M2
DE (HOT SWAP)
Reduced EMI and Reflections
The MAX13448E features reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 500kbps.
Figure 9. Simplified Structure of the Driver Enable Pin (DE)
Hot-Swap Input Circuitry The enable inputs feature hot-swap capability. At the input there are two NMOS devices, M1 and M2 (Figure 9). When VCC ramps from zero, an internal 7s timer turns on M2 and sets the SR latch that also turns on M1. Transistor M2, a 1.5mA current sink, and M1, a 100A current sink, pull DE to GND through a 5k resistor. M2 is designed to pull DE to the disabled state against an external parasitic capacitance up to 100pF that can drive DE high. After 7s, the timer deactivates M2 while M1 remains on, holding DE low against three-state leakages that can drive DE high. M1 remains on until an external source overcomes the required input current. At this time, the SR latch resets and M1 turns off. When M1 turns off, DE reverts to a standard, high-impedance CMOS input.
Line Length
The Telecommunications Industry Association (TIA) publishes the document TSB-89: Application Guidelines for TIA/EIA-485-A that is a good reference for determining maximum data rate vs. line length.
Typical Applications
The MAX13448E transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figure 10 shows a typical network application circuit. To minimize reflections, terminate the line at both ends in its characteristic impedance, and keep stub lengths off the main line as short as possible.
Applications Information
256 Transceivers on the Bus
The RS-485 standard specifies the load each receiver places on the bus in terms of unit loads. An RS-485 compliant transmitter can drive 32 one-unit loads when used with a 120 cable that is terminated on both ends over a common-mode range of -7V to +12V. The
______________________________________________________________________________________
13
80V Fault-Protected Full-Duplex RS-485 Transceiver MAX13448E
A RO RE DE DI D R 120 B Z Z 120 Y A Y Z B A Y Z B A 120 B R DE RE RO 120 Y D DI
R D D
R
MAX13448E
DI
DE RE RO
DI
DE RE RO
Figure 10. Typical Full-Duplex RS-485 Network
Pin Configuration
PROCESS: BiCMOS
TOP VIEW
Chip Information
N.C. 1 RO 2 RE 3 DE 4 DI 5 GND 6 GND 7
+
14 VCC 13 N.C. 12 A 11 B 10 Z 9Y 8 N.C.
MAX13448E
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE S14-5 DOCUMENT NO. 21-0041
SO
14 SO
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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