EVALUATION KIT AVAILABLE
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
General Description
Benefits and Features
The MAX13487E/MAX13488E +5V, half-duplex, ±15kV
ESD-protected RS-485/RS-422-compatible transceivers
feature one driver and one receiver. The MAX13487E/
MAX13488E include a hot-swap capability to eliminate
false transitions on the bus during power-up or live
insertion.
The MAX13487E/MAX13488E feature Maxim’s proprietary AutoDirection control. This architecture makes the
devices ideal for applications, such as isolated RS-485
ports, where the driver input is used in conjunction with
the driver-enable signal to drive the differential bus.
The MAX13487E features reduced slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free transmission up to 500kbps. The MAX13488E driver slew
rate is not limited, allowing transmit speeds up to
16Mbps.
The MAX13487E/MAX13488E feature a 1/4-unit load
receiver input impedance, allowing up to 128 transceivers on the bus. These devices are intended for halfduplex communications. All driver outputs are
protected to ±15kV ESD using the Human Body Model.
The MAX13487E/MAX13488E are available in an 8-pin
SO package. The devices operate over the extended
-40°C to +85°C temperature range.
• AutoDirection Saves Space and BOM Cost
• AutoDirection Enables Driver Automatically on
Transmission, Eliminating an Opto or Other
Discrete Means of Isolation
• 8-Pin SO Package
• Robust Protection Features for Telecom, Industrial,
and Isolated Applications
• Hot-Swap Capability to Eliminate False Transitions
on the Bus During Power-Up or Live Insertion
• Extended ESD Protection for RS-485 I/O Pins
(±15kV Human Body Model)
• Options Optimize Designs for Speed or Errorless
Data Transmission
• Enhanced Slew-Rate Limiting Facilitates ErrorFree Data Transmission (MAX13487E)
• High-Speed Version (MAX13488E) Allows for
Transmission Speeds Up to 16Mbps
• 1/4-Unit Load, Allowing Up to 128 Transceivers on
the Bus
Functional Diagram
MAX13487E
MAX13488E
Applications
Isolated RS-485 Interfaces
1
RO
2
RE
VCC
8
+
R
-
Utility Meters
RE
Industrial Controls
Industrial Motor Drives
3
Automated HVAC Systems
SHDN
-
VDT
B 7
COM
+
Ordering Information/
Selector Guide
PART
PIN-PACKAGE
RI
DI
A 6
STATE
MACHINE
DE
SLEW-RATE
LIMITED
MAX13487EESA+
8 SO
Yes
MAX13488EESA+
8 SO
No
4
D
DI
GND
5
+Denotes a lead(Pb)-free/RoHS-compliant package.
Note: All devices operate over the -40°C to +85°C temperature
range.
Pin Configuration/Typical Application Circuit appear at end
of data sheet.
19-0740; Rev 1; 2/15
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Absolute Maximum Ratings
(All voltages referenced to GND.)
Supply Voltage VCC ...............................................................+6V
SHDN, RE, DI..............................................................-0.3V to +6
A, B........................................................................... -8V to +13V
Short-Circuit Duration (RO, A, B) to GND ..................Continuous
Continuous Power Dissipation (TA = +70°C)
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
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
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 = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
Differential Driver Output
VOD
RDIFF = 100Ω, Figure 1
2.0
RDIFF = 54Ω, Figure 1
1.5
VCC
V
No load
VCC
Driver Common-Mode Output
Voltage
VOC
RL = 100Ω or 54Ω, Figure 1
Driver Disable Threshold
VDT
Figure 2 (Note 2)
Input-High Voltage
VIH
DI, SHDN, RE
Input-Low Voltage
VIL
DI, SHDN, RE
0.8
V
Input Current
IIN
DI, SHDN, RE
±1
µA
Driver Short-Circuit Output
Current
(Note 3)
IOSD
Driver Short-Circuit Foldback
Output Current (Note 3)
IOSDF
VCC / 2
+0.6
3
V
+1
V
2.0
V
0V ≤ VOUT ≤ +12V
+50
+250
-7V ≤ VOUT ≤ 0V
-250
-50
mA
(VCC - 1V) ≤ VOUT ≤ +12V
20
mA
-7V ≤ VOUT ≤ 0V
-20
RECEIVER
Input Current
(A and B)
IA, B
DI = VCC, VCC
= GND or +5V
Receiver Differential Threshold
Voltage
VTH
-7V ≤ VCM ≤ +12V
Receiver Input Hysteresis
ΔVTH
VA + VB = 0V
VIN = +12V
VIN = -7V
250
-200
-200
+200
25
µA
mV
mV
VCC 1.5
Output-High Voltage
VOH
IO = -1.6mA, VA - VB > VTH
Output-Low Voltage
VOL
IO = 1mA, VA - VB < -VTH
0.4
V
Tri-State Output Current at
Receiver
IOZR
0V ≤ VO ≤ VCC
±1
µA
Receiver Input Resistance
RIN
-7V ≤ VCM ≤ +12V
48
Receiver Output Short-Circuit
Current
IOSR
0V ≤ VRO ≤ VCC
±7
www.maximintegrated.com
V
kΩ
±95
mA
Maxim Integrated | 2
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Electrical Characteristics (continued)
(VCC = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER SUPPLY
Supply Voltage
VCC
Supply Current
ICC
Shutdown Supply Current
ISHDN
5.25
V
SHDN = 1, RE = 0, no load
4.75
4.5
mA
SHDN = 0
10
µA
ESD PROTECTION
ESD Protection (A, B)
ESD Protection (All Other Pins)
Air Gap Discharge IEC 61000-4-2
(MAX13487E)
±15
Human Body Model
±15
Human Body Model
±2
kV
kV
Switching Characteristics—MAX13487E
(VCC = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
Driver Propagation Delay
Driver Differential Output Rise or
Fall Time
tDPLH
tDPHL
tHL
tLH
RL = 110Ω, CL = 50pF, Figures 2 and 3
RL = 110Ω, CL = 50pF, Figures 2 and 3
Maximum Data Rate
Driver Disable Delay
200
1000
200
1000
200
900
200
900
500
tDDD
ns
ns
kbps
Figure 3
2500
ns
Driver Enable from Shutdown to
Output High
tDZH(SHDN) Figure 4
5.5
µs
Driver Enable from Shutdown to
Output Low
tDZL(SHDN) Figure 4
5.5
µs
700
ns
Time to Shutdown
tSHDN
50
340
RECEIVER
Receiver Propagation Delay
Receiver Output Skew
tRPLH
tRPHL
tRSKEW
80
CL = 15pF, Figures 5 and 6
80
CL = 15pF, Figure 6
Maximum Data Rate
13
500
ns
ns
kbps
Receiver Enable to Output High
tRZH
Figure 7
50
ns
Receiver Enable to Output Low
tRZL
Figure 7
50
ns
Receiver Disable Time from High
tRHZ
Figure 7
50
ns
Receiver Disable Time from Low
tRLZ
Figure 7
50
ns
Receiver Enable from Shutdown
to Output High
Figure 8
2200
ns
(SHDN)
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tRZH
Maxim Integrated | 3
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Switching Characteristics—MAX13487E (continued)
(VCC = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
Receiver Enable from Shutdown
to Output Low
Receiver Enable Delay
Time to Shutdown
SYMBOL
CONDITIONS
tRZL
(SHDN)
Figure 8
tRED
Figure 3
tSHDN
MIN
50
TYP
340
MAX
UNITS
2200
ns
70
ns
700
ns
MAX
UNITS
Switching Characteristics—MAX13488E
(VCC = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
DRIVER
Driver Propagation Delay
Driver Differential Output Rise or
Fall Time
tDPLH
tDPHL
tHL
tLH
50
15
RL = 110Ω, CL = 50pF, Figures 2 and 3
Maximum Data Rate
Driver Disable Delay
50
RL = 110Ω, CL = 50pF, Figures 2 and 3
15
16
ns
Mbps
Figure 3
70
ns
Driver Enable from Shutdown to
Output High
tDZH(SHDN) Figure 4
2.2
µs
Driver Enable from Shutdown to
Output Low
tDZL(SHDN) Figure 4
2.2
µs
700
ns
Time to Shutdown
tDDD
ns
tSHDN
50
340
RECEIVER
Receiver Propagation Delay
Receiver Output Skew
tRPLH
tRPHL
tRSKEW
80
CL = 15pF, Figures 5 and 6
80
CL = 15pF, Figure 6
Maximum Data Rate
13
16
ns
ns
Mbps
Receiver Enable to Output High
tRZH
Figure 7
50
ns
Receiver Enable to Output Low
tRZL
Figure 7
50
ns
Receiver Disable Time from High
tRHZ
Figure 7
50
ns
Receiver Disable Time from Low
tRLZ
Figure 7
50
ns
Receiver Enable from Shutdown
to Output High
Figure 8
2200
ns
(SHDN)
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tRZH
Maxim Integrated | 4
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Switching Characteristics—MAX13488E (continued)
(VCC = +5V ±5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
Receiver Enable from Shutdown
to Output Low
CONDITIONS
MIN
TYP
MAX
UNITS
tRZL
(SHDN)
Figure 8
2200
ns
tRED
Figure 3
70
ns
700
ns
Receiver Enable Delay
Time to Shutdown
tSHDN
50
340
Note 1: All currents into the device are positive. All currents out of the device are negative. All voltages referred to device ground,
unless otherwise noted.
Note 2: This is a differential voltage from A to B that the driving device must see on the bus to disable its driver.
Note 3: The short-circuit output current applied to peak current just prior to foldback current limiting. The short-circuit foldback output current applies during current limiting to allow a recovery from bus contention.
Typical Operating Characteristics
(VCC = +5.0V, TA = +25°C, unless otherwise noted.)
3.6
3.4
21
14
7
3.2
-15
10
35
60
MAX13487Etoc03
30
20
0
1
0
85
2
3
4
0
5
1
2
3
4
TEMPERATURE (°C)
OUTPUT-HIGH VOLTAGE (V)
OUTPUT-LOW VOLTAGE (V)
RECEIVER OUTPUT-HIGH VOLTAGE
vs. TEMPERATURE
RECEIVER OUTPUT-LOW
VOLTAGE vs. TEMPERATURE
DIFFERENTIAL OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
5.0
4.8
4.6
4.4
IO = 1mA
0.4
0.3
0.2
0.1
5
80
MAX13487Etoc06
5.2
0.5
OUTPUT CURRENT (mA)
IO = 1mA
MAX13487Etoc05
MAX13487Etoc04
5.4
OUTPUT-LOW VOLTAGE (V)
-40
40
10
0
3.0
OUTPUT-HIGH VOLTAGE (V)
50
OUTPUT CURRENT (mA)
28
OUTPUT CURRENT (mA)
3.8
60
MAX13487Etoc02
NO LOAD
SUPPLY CURRENT (mA)
35
MAX13487Etoc01
4.0
OUTPUT CURRENT
vs. RECEIVER OUTPUT-LOW VOLTAGE
OUTPUT CURRENT
vs. RECEIVER OUTPUT-HIGH VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
60
40
20
4.2
0
4.0
-40
-15
10
35
TEMPERATURE (°C)
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60
85
0
-40
-15
10
35
TEMPERATURE (°C)
60
85
0
1
2
3
4
5
OUTPUT VOLTAGE (V)
Maxim Integrated | 5
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Typical Operating Characteristics (continued)
(VCC = +5.0V, TA = +25°C, unless otherwise noted.)
2.0
1.5
1.0
0.5
60
40
-15
10
35
60
60
40
0
-7 -6 -5 -4 -3 -2 -1 0
85
80
20
0
-40
1
2
3
4
0
5
2
4
6
8
10
12
OUTPUT-LOW VOLTAGE (V)
SHUTDOWN CURRENT vs. TEMPERATURE
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
7
6
5
4
3
2
RL = 10kΩ
800
tDPLH
600
400
200
tDPHL
1
0
600
DRIVER PROPAGATION DELAY (ns)
8
1000
DRIVER PROPAGATION DELAY (ns)
MAX13487Etoc10
9
0
-40
-15
10
35
60
85
MAX13487Etoc12
OUTPUT-HIGH VOLTAGE (V)
MAX13487Etoc11
TEMPERATURE (°C)
10
RL = 110Ω
tDPLH
500
400
300
200
tDPHL
100
0
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
RECEIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
25
20
15
10
tDPLH
5
30
RL = 110Ω
25
20
15
10
tDPLH
-15
10
35
TEMPERATURE (°C)
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60
85
tRPHL
30
15
tRPLH
tDPHL
0
0
-40
45
5
tDPHL
0
60
MAX13487Etoc15
RL = 10kΩ
DRIVER PROPAGATION DELAY (ns)
30
MAX13487Etoc14
TEMPERATURE (°C)
MAX13487Etoc13
TEMPERATURE (°C)
PROPAGATION DELAY (ns)
SHUTDOWN CURRENT (μA)
80
20
0
DRIVER PROPAGATION DELAY (ns)
100
OUTPUT CURRENT (mA)
100
OUTPUT CURRENT (mA)
2.5
120
MAX13487Etoc08
RDIFF = 54Ω
DIFFERENTIAL OUTPUT VOLTAGE (V)
120
MAX13487Etoc07
3.0
OUTPUT CURRENT
vs. TRANSMITTER OUTPUT-LOW VOLTAGE
OUTPUT CURRENT
vs. TRANSMITTER OUTPUT-HIGH VOLTAGE
MAX13487Etoc09
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
-40
-15
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
Maxim Integrated | 6
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Typical Operating Characteristics (continued)
(VCC = +5.0V, TA = +25°C, unless otherwise noted.)
30
MAX13487Etoc18
MAX13487Etoc16
RECEIVER PROPAGATION (ns)
40
DRIVER PROPAGATION (16Mbps)
(MAX13488E)
DRIVER PROPAGATION (500kbps)
(MAX13487E)
MAX13487Etoc17
RECEIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
DI
2V/div
DI
2V/div
tRPLH
20
tRPHL
A-B
5V/div
A-B
5V/div
10
WAVEFORM INTENSITY: 68%
0
-40
-15
10
35
60
85
10ns/div
400ns/div
TEMPERATURE (°C)
MAX13487Etoc19
MAX13487Etoc20
DRIVING 16nF (19.2kbps)
(MAX13487E)
RECEIVER PROPAGATION (16Mbps)
(MAX13488E)
B
2V/div
DI
2V/div
A
2V/div
A-B
5V/div
RO
2V/div
10μs/div
10ns/div
MAX13487Etoc21
MAX13487Etoc22
DRIVING 16nF (750kbps)
(MAX13488E)
DRIVING 16nF (19.2kbps)
(MAX13488E)
DI
2V/div
A-B
5V/div
A-B
5V/div
10μs/div
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DI
2V/div
400ns/div
Maxim Integrated | 7
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Test Circuits and Waveforms
A
RDIFF
RL
2
DI
VOD
CL
A
VCC
GND
VID
B
RDIFF
CL
RL
2 VOC
B
Figure 2. Driver-Timing Test Circuit
Figure 1. Driver DC Test Load
RE = VCC
VCC
f = 1MHz, tLH ≤ 3ns, tHL ≤ 3ns
1.5V
DI
1.5V
0
tDPLH
1/2 VO
tDPHL
B
VO
A
1/2 VO
RO
O
tDDD, tRED
(RO PULLED LOW)
VDIFF = V(A) - V(B)
VO
VDIFF
90%
90%
0
10%
10%
-VO
tLH
tHL
Figure 3. Driver Propagation Delays
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Maxim Integrated | 8
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Test Circuits and Waveforms (continued)
VCC
1.5V
SHDN
0
tDZL(SHDN)
A, B
500Ω
OUTPUT
UNDER TEST
S1
CL
VCC
2.3V OUTPUT NORMALLY LOW
VOL
S2
OUTPUT NORMALLY HIGH
A, B
2.3V
0
tDZH(SHDN)
Figure 4. Driver Enable and Disable Times
B
R
VID
ATE
RECEIVER
OUTPUT
A
Figure 5. Receiver-Propagation-Delay Test Circuit
A
f = 1MHz, tLH ≤ 3ns, tHL ≤ 3ns
1V
-1V
B
tRPLH
tRPHL
VOH
RO
1.5V
VOL
1.5V
tRSKEW = | tRPHL - tRPLH |
Figure 6. Receiver Propagation Delays
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Maxim Integrated | 9
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Test Circuits and Waveforms (continued)
VCC
RE
1.5V
1.5V
0
tRZL(SHDN), tRZL
tRHZ
VCC
RO
2.3V
0
VOH + 0.5V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
VCC
2.3V
RO
VOH + 0.5V
0
tRZH(SHDN), tRZH
DI = 0V
tRHZ
Figure 7. Receiver Enable and Disable Times
VCC
1.5V
SHDN
0
tRZL(SHDN)
VCC
500Ω
RO
CL
S1
VCC
2.3V
RO
0
S2
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
VCC
2.3V
RO
0
tRZH(SHDN)
DI = 1
Figure 8. Receiver Enable Time from Shutdown
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Maxim Integrated | 10
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Pin Description
PIN
NAME
1
RO
Receiver Output. When receiver is enabled and V(A) - V(B) > +200mV, RO is high. If V(A) - V(B)
< -200mV, RO is low.
2
RE
Receiver Output Enable. Drive RE low to enable the RO. Drive RE high to let the AutoDirection circuit
control the receiver. RE is a hot-swap input (see the Hot-Swap Capability section for more details).
3
SHDN
Shutdown. Drive SHDN high to let the device operate in normal operation. Drive SHDN low to put the part
in shutdown.
4
DI
Driver Input. Drive DI low to force noninverting output low and inverting output high. Drive DI high to force
noninverting output high and inverting output low. DI is an input to the internal state machine that
automatically enables and disables the driver. See the Function Tables and General Description for more
information. DI is a hot-swap input (see the Hot-Swap Capability section for more details).
5
GND
6
A
7
B
8
VCC
FUNCTION
Ground
Noninverting Receiver Input and Noninverting Driver Output
Inverting Receiver Input and Inverting Driver Output
Positive Supply, VCC = +5V ±5%. Bypass VCC to GND with a 0.1µF capacitor.
Function Tables
TRANSMITTING
INPUTS
OUTPUTS
SHDN
DI
A-B > VDT
ACTION
A
1
0
X
Turn driver ON
0
1
1
1
False
If driver was OFF, keep it OFF
HIGH IMPEDANCE
HIGH IMPEDANCE
1
1
False
If driver was ON, keep it ON
1
0
1
1
True
Turn driver OFF
HIGH IMPEDANCE
HIGH IMPEDANCE
0
X
X
X
B
SHUTDOWN
RECEIVING
INPUTS
OUTPUT
SHDN
RE
A-B
DRIVER STATE
RECEIVER STATE
RO
1
0
≥+200mV
X
ON
1
1
0
≤-200mV
X
ON
0
1
1
X
ON
OFF
HIGH IMPEDANCE
1
1
≥+200mV
OFF
ON
1
1
1
≤-200mV
OFF
ON
0
0
X
X
X
X
SHUTDOWN
X = Don’t care, shutdown mode, driver, and receiver outputs are in high impedance.
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Maxim Integrated | 11
MAX13487E/MAX13488E
Detailed Description
The MAX13487E/MAX13488E half-duplex, high-speed
transceivers for RS-485/RS-422 communication contain
one driver and one receiver. The MAX13487E/
MAX13488E feature a hot-swap capability allowing line
insertion without erroneous data transfer (see the HotSwap Capability section). The MAX13487E features
reduced slew-rate drivers that minimize EMI and
reduce reflections caused by improperly terminated
cables, allowing error-free transmission up to 500kbps.
The MAX13488E driver slew rate is not limited, making
data throughput of up to 16Mbps possible.
AutoDirection Circuitry
Internal circuitry in the MAX13487E/MAX13488E, in
conjunction with an external pullup resistor on A and
pulldown resistor on B (see Typical Application Circuit ),
act to automatically disable or enable the driver and
receiver to keep the bus in the correct state. This
AutoDirection circuitry consists of a state machine and
an additional receive comparator that determines
whether this device is trying to drive the bus, or another
node on the network is driving the bus.
The internal state machine has two inputs:
• DI
• The current state of A-B (determined by a dedicated
differential comparator)
The state machine also has two outputs:
• DRIVER_ENABLE—Internal signal that enables and
disables the driver
• RECEIVER_ENABLE—Internal signal that is the
inverse of the DRIVER_ENABLE signal, but it can be
overridden by an external pin
When DI is low, the device always drives the bus low.
When DI is high, the device drives the bus for a short
time, then disables the driver and allows the external
pullup/pulldown resistors to hold the bus in the high
state (A-B > 200mV). During each low-to-high transition
of DI, the driver stays enabled until (A-B) > VDT, and
then disables the driver, letting the pullup/pulldown
resistors hold the A and B lines in the correct state.
Pullup and Pulldown Resistors
The pullup and pulldown resistors on the A and B lines
are required for proper operation of the device
although their exact value is not critical. They function
to hold the bus in the high state (A-B > 200mV) following a low-to-high transition. Sizing of these resistors is
determined in the same way as when using any other
RS-485 driver and depends on how the line is terminated and how many nodes are on the bus. The most
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Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
important factor when sizing these resistors is to guarantee that the idle voltage on the bus (A-B) is greater
than 200mV in order to remain compatible with standard RS-485 receiver thresholds.
Idle State
When not transmitting data, the MAX13487E/
MAX13488E require the DI input be driven high to
remain in the idle state. A conventional RS-485 transceiver has DE and RE inputs that are used to enable
and disable the driver and receiver. However, the
MAX13487E/MAX13488E does not have a DE input,
and instead uses an internal state machine to enable
and disable the drivers. DI must be driven high in order
to go to the idle state.
Hot-Swap Capability
Hot-Swap Inputs
When circuit boards are inserted into a hot or powered
back plane, differential 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 DI and RE inputs of these
devices to a defined logic level. Leakage currents up to
±10µA 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 circuit-board 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.
To overcome both these problems, two different pullup
switches (strong and weak) are turned on during the
power-up. When VCC rises, an internal power-up signal
enables a strong pullup circuit. It holds DI and RE high
with 1mA for 15µs. Once the timeout is expired, this
strong pullup is switched off. A weak pullup (100µA)
remains active to overcome leakage on the pin. This
second weak pullup disappears as soon as the microcontroller forces a low state on these pins. Therefore, in
normal operation (after the first activation), these pins
can be considered as high-impedance pins (CMOS
inputs) without any pullup circuitry.
The AutoDirection state machine is initialized, forcing the
driver disabled. The receiver is enabled in AutoDirection
mode.
Hot-Swap Input Circuitry
The enable inputs feature hot-swap capability. At the
input there are two pMOS devices, M1 and M2 (Figure 9).
When VCC ramps from zero, an internal 15µs timer turns
Maxim Integrated | 12
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
on M2 and sets the SR latch, which also turns on M1.
Transistors M2, a 1.5mA current source, and M1, a 500µA
current source, pull RE to VCC through a 5kΩ resistor. M2
is designed to pull RE to the disabled state against an
external parasitic capacitance up to 100pF that can drive
RE high. After 15µs, the timer deactivates M2 while M1
remains on, holding DI high against three-state leakages
that can drive RE low. 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,
RE reverts to a standard, high-impedance CMOS input.
Whenever VCC drops below 1V, the hot-swap input is
reset. DI has similar hot-swap circuitry.
VCC
15μs
TIMER
SR LATCH
TIMER
±15kV 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
MAX13487E/MAX13488E have extra protection against
static electricity. Maxim’s engineers have developed
state-of-the-art structures to protect these pins against
ESD of ±15kV without damage. The ESD structures
withstand high ESD in all states: normal operation, shutdown, and powered down. After an ESD event, the
MAX13487E/MAX13488E keep working without latchup
or damage.
ESD protection can be tested in various ways. The
transmitter outputs and receiver inputs of the
MAX13487E/MAX13488E are characterized for protection to the following limits:
• ±15kV using the Human Body Model
• ±15kV using the Air Gap Discharge Method specified in IEC 61000-4-2 (MAX13487E only)
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 10a shows the Human Body Model, and Figure
10b 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 1.5kΩ resistor.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD testing and
performance of finished equipment. However, it does
not specifically refer to integrated circuits. The
MAX13487E/MAX13488E help you design equipment to
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5kΩ
RE
(HOT SWAP)
RE
100μA
500μA
M2
M1
VCC
Figure 9. Simplified Structure of the Receiver Enable Pin (RE)
meet IEC 61000-4-2 without the need for additional
ESD-protection components.
The major difference between tests done using the
Human Body Model and IEC 61000-4-2 is higher peak
current in IEC 61000-4-2 because series resistance is
lower in the IEC 61000-4-2 model. Hence, the ESD
withstand voltage measured to IEC 61000-4-2 is generally lower than that measured using the Human Body
Model. Figure 10c shows the IEC 61000-4-2 model,
and Figure 10d shows the current waveform for IEC
61000-4-2 ESD Contact Discharge test.
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. Of course, all pins require this protection, not just RS-485 inputs and outputs.
The Air-Gap test involves approaching the device with a
charged probe. The Contact-Discharge method connects
the probe to the device before the probe is energized.
Maxim Integrated | 13
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
RC
1MΩ
CHARGE-CURRENTLIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
RD
1500Ω
RC
50MΩ TO 100MΩ
DISCHARGE
RESISTANCE
CHARGE-CURRENTLIMIT RESISTOR
DEVICE
UNDER
TEST
STORAGE
CAPACITOR
Figure 10a. Human Body ESD Test Model
IP 100%
90%
Cs
150pF
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 10c. IEC 61000-4-2 ESD Test Model
I
100%
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
IPEAK
Ir
HIGHVOLTAGE
DC
SOURCE
RD
330Ω
AMPS
36.8%
10%
0
10%
0
tRL
TIME
tr = 0.7ns TO 1ns
tDL
CURRENT WAVEFORM
t
30ns
60ns
Figure 10b. Human Body Current Waveform
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
Applications Information
Low-Power Shutdown Mode
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12kΩ
(1-unit load), and the standard driver can drive up to
32-unit loads. The MAX13487E/MAX13488E have a 1/4unit load receiver input impedance (48kΩ), allowing up
to 128 transceivers to be connected in parallel on one
communication line. Any combination of these devices,
as well as other RS-485 transceivers with a total of 32unit loads or fewer, can be connected to the line.
Reduced EMI and Reflections
The MAX13487E features reduced slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free data
transmission up to 500kbps.
Low-power shutdown mode is initiated by bringing
SHDN low. In shutdown, the devices draw a maximum
of 10µA of supply current.
The devices are guaranteed not to enter shutdown if
SHDN is low for less than 50ns. If the inputs are in this
state for at least 700ns, the devices are guaranteed to
enter shutdown.
Enable times tZH and tZL (see the Switching Characteristics section) assume the devices were not in a lowpower shutdown state. Enable times t ZH(SHDN) and
tZL(SHDN) assume the devices were in shutdown state. It
takes drivers and receivers longer to become enabled
from low-power shutdown mode (tZH(SHDN), tZL(SHDN))
than from driver/receiver-disable mode (tZH, tZL).
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft.
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Maxim Integrated | 14
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
VCC
DI
D
VCC
Rt
SHDN
RO
RE
D
Rt
VCC
SHDN
VCC
R
R
MAX13487E
MAX13488E
R
RO
RE
R
D
D
DI
DI
SHDN
RO
RE
DI SHDN
RO
RE
Figure 11. Typical Half-Duplex RS-485 Network
Typical Applications
The MAX13487E/MAX13488E transceivers are
designed for half-duplex, bidirectional data communications on multipoint bus transmission lines. Figure 11
shows a typical network application. 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. The slew-rate-limited MAX13487E is
more tolerant of imperfect termination.
Circuit shows an isolated RS-485 interface using the
MAX13487E/MAX13488E. The transceiver is powered
separately from the controlling circuitry. The
AutoDirection feature of the MAX13487E/MAX13488E
(see the AutoDirection Circuitry section), replaces an
external relay allowing faster switching speeds, no contact bounce, better reliability, and better electrical isolation. The MAX13487E/MAX13488E only require two
optocouplers to electrically isolate the transceiver.
Isolated RS-485 Interface
An isolated RS-485 interface electrically isolates different nodes on the bus to protect the bus from problems
due to high common-mode voltages that exceed the
RS-485 common-mode voltage range, conductive
noise, and ground loops. The Typical Application
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Chip Information
PROCESS: BiCMOS
Maxim Integrated | 15
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Pin Configuration/Typical Application Circuit
VSYS
RXD
VISO
VCC
0.1μF
RO
VISO VISO
RE
VSYS
SHDN
DI
+
1
8
R
2
7
3
6
4
D
A
VCC
5
GND
SO
TXD
B
Rt
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or
“-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
LAND PATTERN NO.
8 SO
S8+2
21-0041
90-0096
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Maxim Integrated | 16
Half-Duplex RS-485-/RS-422Compatible Transceiver with
AutoDirection Control
MAX13487E/MAX13488E
Revision History
PAGES
CHANGED
REVISION
NUMBER
REVISION
DATE
0
1/07
Initial release
—
1
2/15
Added the Benefits and Features section
1
DESCRIPTION
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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