General Description
The MAX13448E full-duplex RS-485 transceiver fea-
tures 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 cir-
cuitry, 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 logic-
high 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 elimi-
nate 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
-40°C to +85°C temperature range.
Applications
Industrial Control Systems
HVAC Control systems
Utility Meters
Motor Driver Control Systems
Features
o±80V Fault Protection on the RS-485 I/O Ports
oTrue Fail-Safe Receiver
oHot-Swap Input Structure on DE
oESD Protection on the RS-485 I/O Ports
±8kV Human Body Model
oSlew-Rate Limiting Facilitates Error-Free Data
Transmission
o1/8-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
oAvailable in 14-Pin SO Package
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-4098; Rev 0; 5/08
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.
PART TEMP RANGE PIN-PACKAGE
MAX13448EESD+ -40°C to +85°C 14 SO
Pin Configuration appears at end of data sheet.
+
Denotes a lead-free package.
Rt
RE
RO
Y
Z
DI
9
10
A
B
Rt
12
11
6, 73
R
D
R
DI
D
DE
RE
RO
N.C.
R
D
DE
GND GND
VCC
1μF
141
SO
+VCC
N.C.
132 N.C.RO
123ARE
114BDE
105ZDI
96YGND
87 N.C.GND
1, 8,
13
2
5
414
VCC
MAX13448E
Functional Diagram
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +3.0 to +5.5V, TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA= +25°C.) (Notes 2, 3)
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.
(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= +70°C)
14-Pin SO (derate 8.3mW/°C above +70°C)................667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
VCC Supply Voltage Range VCC 3.0 5.5 V
N o l oad , D E , D I, RE = 0V or V
C C
, V
C C
= 3.3V 15
Supply Current IQNo load, DE, DI, RE = 0V or VCC, VCC = 5V 15 mA
DE = GND, RE = VCC, VCC = 3.3V 100
Supply Current in Shutdown
Mode ISHDN DE = GND, RE = VCC, VCC = 5V 100 µA
DE = GND, RE = GND, short to +60V 15
Supply Current with Output
Shorted to ±60V ISHRT DE = GND, RE = GND, short to -60V 15 mA
DRIVER
RL = 100Ω, Figure 1 2 VCC
Differential Driver Output VOD RL = 54Ω, Figure 1 1.5 VCC
V
Change in Magnitude of
Differential Output Voltage ΔVOD RL = 100Ω or 54Ω, Figure 1 (Note 4) -0.2 0.2 V
Driver Common-Mode Output
Voltage VOC RL = 100Ω or 54Ω, Figure 1 VCC/2 3 V
Change in Magnitude of
Common-Mode Voltage ΔVOC RL = 100Ω or 54Ω, Figure 1 (Note 4) -0.2 +0.2 V
DI = low, 0V ≤ VY or VZ ≤ +12V +250
Driver Short-Circuit Output
Current IOSD DI = high, -7V ≤ VY or VZ ≤ VCC (Note 5) -250 mA
DI = low, (VCC - 1V) ≤ VY or VZ ≤ +12V +10
Driver Short-Circuit Foldback
Output Current IOSDF DI = high, -7V ≤ VY or VZ ≤ +1V -10 mA
VY or VZ ≥ + 22V, RL = 100Ω+6
Driver-Limit Short-Circuit
Foldback Output Current IOSDL VY or VZ ≤ -13V, RL = 100Ω-6 mA
Driver Input High Voltage VDIH 2V
Driver Input Low Voltage VDIL 0.8 V
Driver Input Current IDIN -1 +1 µA
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.
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
_______________________________________________________________________________________ 3
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= +25°C.) (Notes 2, 3)
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
RECEIVER
VA, VB = +12V VCC = GND or
VCC = +3.0V to +5.5V +125 µA
VA, VB = -7V -100 µA
Input Current IA, B
VA, VB = ±80V -6 +6 mA
Receiver Differential Threshold
Voltage VTH -7V ≤ VCM ≤ +12V -200 -50 mV
Receiver Input Hysteresis ΔVTH 25 mV
Output High Voltage VOH IOH = -1.6mA VCC -
0.6 V
Output Low Voltage VOL IOL = 1mA 0.4 V
Three-State Output Current at
Receiver IOZR 0 ≤ VA, VB ≤ VCC -1 +1 µA
Receiver Output Short-Circuit
Current IOSR 0 ≤ VRO ≤ VCC -95 +95 mA
ESD PROTECTION
All Pins Human Body Model ±2 kV
ESD Protection Level
(A and B, Y and Z) Human Body Model ±8 kV
CONTROL
Control Input High Voltage VCIH DE, RE 2V
Control Input Low Voltage VCIL DE, RE 0.8 V
Input Current Latch During First
Rising Edge IIN DE, RE 80 µA
PROTECTION SPECIFICATIONS
Overvoltage Protection A, B, Y, Z -80 +80 V
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
DRIVER
Driver Differential Propagation
Delay
tDPLH,
tDPHL RL = 54Ω, CL = 50pF, Figures 2 and 3 700 1500 ns
Driver Differential Output
Transition Time tLH, tHL RL = 54Ω, CL = 50pF, Figures 2 and 3 250 1200 ns
Differential Driver Output Skew tDSKEW RL = 54Ω, CL = 50pF, tDSKEW = [tDPLH -
tDPHL], Figures 2 and 3 150 200 ns
Maximum Data Rate fMAX 250 kbps
D r i ver E nab l e Ti m e to Outp ut H i g ht
DZH RL = 500Ω, CL = 50pF, Figure 4 2000 ns
SWITCHING CHARACTERISTICS (VCC = +3.3V ±10%)
(TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA= +25°C.)
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
4 _______________________________________________________________________________________
SWITCHING CHARACTERISTICS (VCC = +3.3V ±10%) (continued)
(TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA= +25°C.)
SWITCHING CHARACTERISTICS (VCC = +5V ±10%)
(TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
Driver Disable Time from
Output High tDHZ RL = 500Ω, CL = 50pF, Figure 4 1000 ns
Driver Enable Time from
Shutdown to Output High tDZH
(
SHDN
)
RL = 500Ω, CL = 50pF, Figure 4 8 µs
D r i ver E nab l e Ti m e to Outp ut Low tDZL RL = 500Ω, CL = 50pF, Figure 5 1500 ns
Driver Disable Time from
Output Low tDLZ RL = 500Ω, CL = 50pF, Figure 5 2000 ns
Driver Enable Time from
Shutdown to Output Low tDZL
(
SHDN
)
RL = 500Ω, CL = 50pF, Figure 5 8 µs
Driver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 12 µs
RECEIVER
Receiver Propagation Delay tRPLH,
tRPHL
CL = 20pF, VID = 2V, VCM = 0V,
Figure 6 2000 ns
Receiver Output Skew tRSKEW CL = 20pF, tRSKEW = [tRPLH - tRPHL],
Figure 6 200 ns
Receiver Enable Time to
Output High tRZH RL = 1kΩ, CL = 20pF, Figure 7 1000 ns
Receiver Disable Time from
Output High tRHZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns
Receiver Wake Time from
Shutdown tRWAKE RL = 1kΩ, CL = 20pF, Figure 7 5 µs
Receiver Enable Time to
Output Low tRZL RL = 1kΩ, CL = 20pF, Figure 7 1000 ns
Receiver Disable Time from
Output Low tRLZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns
Receiver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 200 ns
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
DRIVER
Driver Differential Propagation
Delay
tDPLH,
tDPHL RL = 54Ω, CL = 50pF, Figure 3 800 ns
Driver Differential Output
Transition Time tLH, tHL RL = 54Ω, CL = 50pF, Figure 3 100 1200 ns
Differential Driver Output Skew tDSKEW RL = 54Ω, CL = 50pF, tDSKEW = [tDPLH -
tDPHL], Figure 3 200 ns
Maximum Data Rate fMAX 500 kbps
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
_______________________________________________________________________________________ 5
SWITCHING CHARACTERISTICS (VCC = +5V ±10%) (continued)
(TA= TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA= +25°C.)
PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS
D r i ver E nab l e Ti m e to Outp ut H i g ht
DZH RL = 500Ω, CL = 50pF, Figure 4 1500 ns
Driver Disable Time from
Output High tDHZ RL = 500Ω, CL = 50pF, Figure 4 1000 ns
Driver Enable Time from
Shutdown to Output High tDZH
(
SHDN
)
RL = 500Ω, CL = 50pF, Figure 4 8 µs
Driver Enable Time to Output Low tDZL RL = 500Ω, CL = 50pF, Figure 5 1000 ns
Driver Disable Time from
Output Low tDLZ RL = 500Ω, CL = 50pF, Figure 5 2 µs
Driver Enable Time from
Shutdown to Output Low tDZL
(
SHDN
)
RL = 500Ω, CL = 50pF, Figure 5 8 µs
Driver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 12 µs
RECEIVER
Receiver Propagation Delay tRPLH,
tRPHL
CL = 20pF, VID = 2V, VCM = 0V,
Figure 6 2000 ns
Receiver Output Skew tRSKEW CL = 20pF, tRSKEW = [tRPLH - tRPHL],
Figure 6 200 ns
Receiver Enable Time to
Output High tRZH RL = 1kΩ, CL = 20pF, Figure 7 1000 ns
Receiver Disable Time from
Output High tRHZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns
Receiver Wake Time from
Shutdown tRWAKE RL = 1kΩ, CL = 20pF, Figure 7 8 µs
Receiver Enable Time to
Output Low tRZL RL = 1kΩ, CL = 20pF, Figure 7 1000 ns
Receiver Disable Time from
Output Low tRLZ RL = 1kΩ, CL = 20pF, Figure 7 150 ns
Receiver Time to Shutdown tSHDN RL = 500Ω, CL = 50pF 150 ns
Note 2: Parameters are 100% production tested at TA= +25°C, 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: ΔVOD and ΔVOC 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.
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
6 _______________________________________________________________________________________
Typical Operating Characteristics
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
MAX13448E toc01
-40 -15 10 35 60 85
4.05
4.10
4.15
4.20
DE = RE = LOW
A - B = HIGH
DI = FLOATING
RECEIVER OUTPUT SOURCE CURRENT
vs. OUTPUT HIGH VOLTAGE
OUTPUT SOURCE CURRENT (mA)
OUTPUT HIGH VOLTAGE (V)
MAX13448E toc02
0246810
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
DE = RE = LOW
A - B = HIGH
+25°C
+85°C
-40°C
RECEIVER OUTPUT SINK CURRENT
vs. OUTPUT LOW VOLTAGE
OUTPUT SINK CURRENT (mA)
OUTPUT LOW VOLTAGE (V)
MAX13448E toc03
0246810
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
DE = RE = LOW
B - A = HIGH
+85°C
+25°C
-40°C
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
TEMPERATURE (°C)
OUTPUT HIGH VOLTAGE (V)
MAX13448E toc04
-40 -15 10 35 60 85
3.20
3.21
3.22
3.23
3.24
3.25
DE = RE = LOW
A - B = HIGH
ISOURCE = 1mA
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
TEMPERATURE (°C)
OUTPUT LOW VOLTAGE (V)
MAX13448E toc05
-40 -15 10 35 60 85
0.040
0.045
0.050
0.055
0.060
0.065
0.070
0.075
DE = RE = LOW
B - A = HIGH
ISINK = 1mA
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. DIFFERENTIAL OUTPUT CURRENT
DIFFERENTIAL OUTPUT CURRENT (mA)
DIFFERENTIAL OUTPUT VOLTAGE (V)
MAX13448E toc06
0 20406080100
1.0
1.5
2.0
2.5
3.0
3.5
DE = RE = HIGH
DI = HIGH
DRIVER DIFFERENTIAL OUTPUT
VOLTAGE vs. TEMPERATURE
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE (V)
MAX13448E toc07
-40 -15 10 35 60 85
1.86
1.88
1.90
1.92
1.94
DE = RE = HIGH
DI = HIGH
RLOAD = 54Ω
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
SINGLE-ENDED DRIVER OUTPUT
HIGH VOLTAGE vs. SOURCE CURRENT
OUTPUT SOURCE CURRENT (mA)
OUTPUT HIGH VOLTAGE (V)
MAX13448E toc08
0246810
3.10
3.15
3.20
3.25
3.30
3.35
DE = RE = HIGH
DI = HIGH
SINGLE-ENDED DRIVER SINK CURRENT
vs. OUTPUT LOW VOLTAGE
OUTPUT SINK CURRENT (mA)
OUTPUT LOW VOLTAGE (V)
MAX13448E toc09
0246810
0
0.02
0.04
0.06
0.08
0.10
0.12
DE = RE = HIGH
DI = HIGH
SHUTDOWN CURRENT vs. TEMPERATURE
TEMPERATURE (°C)
SHUTDOWN CURRENT (μA)
MAX13448E toc10
-40 -15 10 35 60 85
0
5
10
15
20
25
30
400ns
DRIVER PROPAGATION DELAY (500kbsp)
2V/div
1V/div
MAX13448E toc11
400ns
RECEIVER PROPAGATION DELAY (500kbsp)
1V/div
2V/div
MAX13448E toc12
DRIVER PROPAGATION DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
PROPAGATION DELAY (ns)
MAX13448E toc13
-40 -15 10 35 60 85
300
350
400
450
500
DE = RE = HIGH
RLOAD = 54Ω
CLOAD = 50pF
tDPLH
tDPHL
RECEIVER PROPAGATION DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
PROPAGATION DELAY (ns)
MAX13448E toc14
-40 -15 10 35 60 85
300
325
350
375
400
DE = RE = LOW
CLOAD = 20pF
tRPLH
tRPHL
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
8 _______________________________________________________________________________________
Y
Z
VOD
VOC
RL/2
RL/2
Figure 1. Driver DC Test Load
DI
DE
VCC
Z
Y
VORL
CL
CL
Figure 2. Driver Timing Test Circuit
DI
VCC
0
Z
Y
VO
0
-VO
VO
VCC/2
tDPLH tDPHL
1/2 VO
10%
tLH
90% 90%
1/2 VO
10%
tHL
VOD = V (Y) - V (Z)
VOD
tSKEW = |tDPLH - tDPHL|
Figure 3. Driver Propagation Delays
Pin Description
PIN NAME FUNCTION
1, 8, 13 N.C. No Connection. Not internally connected. Connect N.C. to GND or leave it unconnected.
2 RO Receiver Output. If receiver is enabled and (A - B) ≥ -50mV, RO = high; if (A - B) ≥ -200mV, RO = low.
3RE 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.
4DE
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.
5DI
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.
6, 7 GND Ground
9 Y Noninverting Driver Output
10 Z Inverting Driver Output
11 B Inverting Receiver Input
12 A Noninverting Receiver Input
14 VCC Positive Supply. VCC = +3.0V to +5.5V. Bypass VCC to GND with a 1µF ceramic capacitor as close
to VCC as possible. Typical VCC values are at VCC = +3.3V and VCC = +5.0V.
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
_______________________________________________________________________________________ 9
DE
OUT
tDHZ
0
VCC
VCC/2
0.25V
0
VOH
GENERATOR 50Ω
0 OR VCC
S1
Y
D1
Z
DOUT
tDZH, tDZH(SHDN)
VOM = (0 + VOH)/2
RL = 500Ω
CL
50pF
Figure 4. Driver Enable and Disable Times (tDHZ, tDZH, tDZH(SHDN))
DE
VCC
OUT
tDLZ
0
VCC
VCC/2
GENERATOR 50Ω
D
tDZL, tDZL(SHDN)
VOM = (VOL + VCC)/2
RL = 500Ω
CL
50pF
VOL 0.25V
VCC
0 OR VCC
S1
Y
D1
Z
DOUT
Figure 5. Driver Enable and Disable Times (tDLZ, tDZL, tDZL(SHDN))
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
10 ______________________________________________________________________________________
B
A
RO
VOH
tRPLH tRPHL
VID
CL
20pF
0
ARO
B
VOH + VOL
2
VOL tSKEW = |tRPLH - tRPHL|
R
Figure 6. Receiver Propagation Delays
S1 OPEN
S2 CLOSED
S3 = +1.5V
RO
VCC
0
0
VOH
VOH/2
S1 OPEN
S2 CLOSED
S3 = +1.5V VCC
0
0
VOH
0.25V
VCC/2
S1 CLOSED
S2 OPEN
S3 = -1.5V
VCC
0
VOL
VCC
VCC/2
S1 CLOSED
S2 OPEN
S3 = -1.5V VCC
0
VOL
VCC
*DE =
LOW
0.25V
GENERATOR
VCC
+1.5V
1kΩ
CL
20pF S2
S1
50Ω
S3 A
B
-1.5V R
VID
RE
RO
RE
RO
RE
RO
RE
tRZH, tRWAKE*
tRLZ, tSHDN*
tRZL, tSHDN*
tRHZ, tSHDN*
(VOL + VCC)/2
VCC/2
RRO
RE
Figure 7. Receiver Enable and Disable Times
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 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. The device
has a hot-swap input structure that prevents distur-
bances 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 transmis-
sion up to 500kbps.
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-imped-
ance state.
Receiver
The receiver accepts a differential, RS-485/RS-422
level input (A and B), and translates it to a single-
ended, logic-level output (RO). Deasserting the receiv-
er 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 maxi-
mum of 100µA of supply current.
The device is guaranteed to not enter shutdown if DE is
low and RE is high for 1µs. If the inputs are in this state
for at least 1ms, the device is guaranteed to enter shut-
down. In the shutdown state, the driver outputs (A and
B) as well as the receiver output (RO) are in a high-
impedance state.
±80V Fault Protection
In certain applications, such as industrial control, driver
outputs and receiver inputs of an RS-485 device some-
times 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 guar-
anteed 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, regard-
less of the presence of a termination resistor. While the
MAX13448E is not damaged by up to ±80V common-
mode 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 out-
put 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
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
______________________________________________________________________________________ 11
TRANSMITTING
INPUT OUTPUT
RE DE DI Z Y
X10 1 0
X11 0 1
00X High
Impedance
High
Impedance
1 0 X High Impedance (Shutdown)
RECEIVING
INPUT OUTPUT
RE DE A - B RO
0 X -50mV 1
0 X -200mV 0
1 1 X Disabled
1 0 X High Impedance (Shutdown)
X = Don’t care; shutdown mode, driver, and receiver outputs are
high impedance.
Table 1. Function Table
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
12 ______________________________________________________________________________________
CHARGE-CURRENT-
LIMIT RESISTOR
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Cs
100pF
RC
1MΩ
RD
1500Ω
HIGH-
VOLTAGE
DC
SOURCE
DEVICE
UNDER
TEST
Figure 8a. Human Body ESD Test Model
IP 100%
90%
36.8%
tRL TIME
tDL
CURRENT WAVEFORM
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
Ir
10%
0
0
AMPS
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.
±8kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electro-
static discharges encountered during handling and
assembly. The driver outputs and receiver inputs of the
MAX13448E have extra protection against static elec-
tricity. Maxim’s engineers have developed state-of-the-
art 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 protec-
tion can be tested in various ways. The transmitter out-
puts and receiver inputs of the MAX13448E are
characterized for protection to the following limits:
• ±8kV using the Human Body Model
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 dis-
charged 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
1.5kΩresistor.
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults or by bus con-
tention. 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 sec-
ond, a thermal-shutdown circuit, forces the driver out-
puts into a high-impedance state if the die temperature
exceeds +160°C (typ).
Hot-Swap Capability
Hot-Swap Inputs
When circuit boards are inserted into a powered back-
plane, 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 logic-
output drivers are high impedance and are unable to
drive the DE input of the device to a defined logic level.
Leakage currents up to ±10µA from the high-imped-
ance 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 circuit-
board capacitance could cause coupling of VCC or
GND to the enable inputs. Without the hot-swap capa-
bility, these factors could improperly enable the trans-
ceiver’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.
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
______________________________________________________________________________________ 13
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 7µs timer
turns on M2 and sets the SR latch that also turns on M1.
Transistor M2, a 1.5mA current sink, and M1, a 100µA
current sink, pull DE to GND through a 5kΩresistor. M2
is designed to pull DE to the disabled state against an
external parasitic capacitance up to 100pF that can
drive DE high. After 7µs, the timer deactivates M2 while
M1 remains on, holding DE low against three-state leak-
ages 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.
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 120Ωcable that is terminated on both ends
over a common-mode range of -7V to +12V. The
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 transmis-
sion line design. In most cases, a single, controlled-
impedance 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.
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.
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 bidirec-
tional data communications on multipoint bus transmis-
sion 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.
DE DE
(HOT SWAP)
5kΩ
TIMER
TIMER
VCC
10μs
M2M1
500μA
100μA
SR LATCH
Figure 9. Simplified Structure of the Driver Enable Pin (DE)
Chip Information
PROCESS: BiCMOS
Figure 10. Typical Full-Duplex RS-485 Network
RO
DI
DE
R120Ω
120Ω
D
MAX13448E
RE
RO
DI
DE
R
D
RE
120Ω
120Ω
A
B
Z
Y
A
B
Z
Y
RO
DI DE
R
D
RE
YZBA
RO
DI DE
R
D
RE
YZBA
MAX13448E
141
TOP VIEW
SO
+VCC
N.C.
132 N.C.RO
123ARE
114BDE
105ZDI
96YGND
87 N.C.GND
Pin Configuration
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
14 SO S14-5 21-0041
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages.
MAX13448E
±80V Fault-Protected Full-Duplex
RS-485 Transceiver
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
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