MAX13487E_15 [MAXIM]
Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control;
| 型号： | MAX13487E_15 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Half-Duplex RS-485-/RS-422-Compatible Transceiver with AutoDirection Control |
| 文件： | 总17页 (文件大小：453K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0740; Rev 0; 1/07
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
General Description
Features
The MAX13487E/MAX13488E +5V, half-duplex, 15ꢀV
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.
♦ +5V Operation
♦ AutoDirection Enables Driver Automatically on
Transmission
♦ Hot-Swappable for Telecom Applications
♦ Enhanced Slew-Rate Limiting Facilitates Error-
Free Data Transmission (MAX13487E)
♦ High-Speed Version (MAX13488E) Allows for
Transmission Speeds Up to 16Mbps
♦ Extended ESD Protection for RS-485 I/O Pins
15ꢀV Human ꢁody Model
The MAX13487E/MAX13488E feature Maxim’s propri-
etary AutoDirection control. This architecture maꢀes 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.
♦ 1/4-Unit Load, Allowing Up to 128 Transceivers on
the ꢁus
The MAX13487E features reduced slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free trans-
mission up to 500ꢀbps. The MAX13488E driver slew
rate is not limited, allowing transmit speeds up to
16Mbps.
♦ 8-Pin SO Pacꢀage
Ordering Information/
Selector Guide
The MAX13487E/MAX13488E feature a 1/4-unit load
receiver input impedance, allowing up to 128 trans-
ceivers on the bus. These devices are intended for half-
duplex communications. All driver outputs are
protected to 15ꢀV ESD using the ꢁuman ꢂody Model.
The MAX13487E/MAX13488E are available in an 8-pin
SO pacꢀage. The devices operate over the extended
-40°C to +85°C temperature range.
PIN-
PACKAGE
SLEW-RATE
LIMITED
PKG
CODE
PART
MAX13487EESA+ 8 SO
MAX13488EESA+ 8 SO
Yes
No
S8-2
S8-2
+Denotes a lead-free package
All devices operate over the -40°C to +85°C temperature range.
Applications
Functional Diagram
Isolated RS-485 Interfaces
Utility Meters
MAX13487E
MAX13488E
8
Industrial Controls
V
CC
+
-
Industrial Motor Drives
Automated ꢁVAC Systems
1
2
RO
RE
R
RE
3
7
6
B
SHDN
-
V
DT
COM
Pin Configuration and Typical Application Circuit appear at
end of data sheet.
A
+
STATE
MACHINE
RI
DI
DE
4
D
DI
5
GND
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
AꢁSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND.)
Operating Temperature Range ...........................-40°C to +85°C
Supply Voltage V ...............................................................+6V
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering 10s) ..................................+300°C
CC
SHDN, RE, DI..............................................................-0.3V to +6
A, ꢂ........................................................................... -8V to +13V
Short-Circuit Duration (RO, A, ꢂ) to GND ..................Continuous
Continuous Power Dissipation (T = +70°C)
A
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
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
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.) (Note 1)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
R
R
= 100Ω, Figure 1
2.0
1.5
V
V
DIFF
CC
Differential Driver Output
V
V
= 54Ω, Figure 1
V
V
OD
OC
DIFF
No load
CC
3
Driver Common-Mode Output
Voltage
R = 100Ω or 54Ω, Figure 1
L
V
/ 2
CC
Driver Disable Threshold
Input-ꢁigh Voltage
Input-Low Voltage
Input Current
V
Figure 2 (Note 2)
DI, SHDN, RE
DI, SHDN, RE
DI, SHDN, RE
+0.6
2.0
+1
V
V
DT
V
Iꢁ
V
0.8
1
V
IL
I
µA
IN
Driver Short-Circuit Output
Current
(Note 3)
0V ≤ V
≤ +12V
≤ 0V
+50
+250
-50
OUT
I
mA
mA
OSD
-7V ≤ V
-250
20
OUT
(V
CC
- 1V) ≤ V
≤ +12V
OUT
Driver Short-Circuit Foldbacꢀ
Output Current (Note 3)
I
OSDF
-7V ≤ V
≤ 0V
-20
OUT
RECEIVER
V
V
= +12V
= -7V
250
IN
IN
Input Current
(A and ꢂ)
DI = V , V
CC CC
= GND or +5V
I
µA
A, ꢂ
-200
-200
Receiver Differential Threshold
Voltage
V
-7V ≤ V ≤ +12V
+200
mV
mV
V
Tꢁ
CM
Receiver Input ꢁysteresis
Output-ꢁigh Voltage
Output-Low Voltage
∆V
V
+ V = 0V
25
Tꢁ
A
ꢂ
V
-
CC
V
I
= -1.6mA, V - V > V
O A ꢂ Tꢁ
Oꢁ
1.5
V
I
O
= 1mA, V - V < -V
0.4
1
V
OL
A
ꢂ
Tꢁ
Tri-State Output Current at
Receiver
I
0V ≤ V ≤ V
µA
ꢀΩ
mA
OZR
O
CC
Receiver Input Resistance
R
-7V ≤ V
≤ +12V
48
7
IN
CM
Receiver Output Short-Circuit
Current
I
0V ≤ V
≤ V
CC
95
OSR
RO
2
_______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
ELECTRICAL CHARACTERISTICS (continued)
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.) (Note 1)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
POWER SUPPLY
Supply Voltage
V
4.75
5.25
4.5
10
V
CC
Supply Current
I
SHDN = 1, RE = 0, no load
SHDN = 0
mA
µA
CC
Shutdown Supply Current
ESD PROTECTION
I
SHDN
Air Gap Discharge IEC61000-4-2
(MAX13487E)
15
ESD Protection (A, ꢂ)
ꢀV
ꢀV
ꢁuman ꢂody Model
ꢁuman ꢂody Model
15
2
ESD Protection (All Other Pins)
SWITCHING CHARACTERISTICS—MAX13487E
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
t
t
200
200
200
200
500
1000
1000
900
DPLꢁ
Driver Propagation Delay
R = 110Ω, C = 50pF, Figures 2 and 3
ns
ns
L
L
DPꢁL
t
t
ꢁL
Driver Differential Output Rise or
Fall Time
R = 110Ω, C = 50pF, Figures 2 and 3
L
L
900
Lꢁ
Maximum Data Rate
Driver Disable Delay
ꢀbps
ns
t
Figure 3
Figure 4
2500
5.5
DDD
Driver Enable from Shutdown to
Output ꢁigh
t
µs
DZꢁ(SꢁDN)
Driver Enable from Shutdown to
Output Low
t
Figure 4
5.5
µs
ns
DZL(SꢁDN)
Time to Shutdown
t
50
340
700
SꢁDN
RECEIVER
t
80
80
13
RPLꢁ
Receiver Propagation Delay
C = 15pF, Figures 5 and 6
ns
L
t
RPꢁL
Receiver Output Sꢀew
t
C = 15pF, Figure 6
L
ns
ꢀbps
ns
RSKEW
Maximum Data Rate
500
Receiver Enable to Output ꢁigh
Receiver Enable to Output Low
Receiver Disable Time from ꢁigh
Receiver Disable Time from Low
t
t
Figure 7
Figure 7
Figure 7
Figure 7
50
50
50
50
RZꢁ
t
ns
RZL
ns
RꢁZ
t
ns
RLZ
Receiver Enable from Shutdown
to Output ꢁigh
t
RZꢁ
Figure 8
2200
ns
(SꢁDN)
_______________________________________________________________________________________
3
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
SWITCHING CHARACTERISTICS—MAX13487E (continued)
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
Receiver Enable from Shutdown
to Output Low
t
RZL
(SꢁDN)
Figure 8
Figure 3
2200
ns
Receiver Enable Delay
Time to Shutdown
t
70
ns
ns
RED
t
50
340
700
SꢁDN
SWITCHING CHARACTERISTICS—MAX13488E
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
t
t
50
50
15
15
DPLꢁ
Driver Propagation Delay
R = 110Ω, C = 50pF, Figures 2 and 3
ns
ns
L
L
DPꢁL
t
t
ꢁL
Driver Differential Output Rise or
Fall Time
R = 110Ω, C = 50pF, Figures 2 and 3
L
L
Lꢁ
Maximum Data Rate
Driver Disable Delay
16
Mbps
ns
t
Figure 3
Figure 4
70
DDD
Driver Enable from Shutdown to
Output ꢁigh
t
2.2
µs
DZꢁ(SꢁDN)
Driver Enable from Shutdown to
Output Low
t
Figure 4
2.2
µs
ns
DZL(SꢁDN)
Time to Shutdown
t
50
16
340
700
SꢁDN
RECEIVER
t
80
80
13
RPLꢁ
Receiver Propagation Delay
C = 15pF, Figures 5 and 6
L
ns
t
RPꢁL
Receiver Output Sꢀew
t
C = 15pF, Figure 6
L
ns
Mbps
ns
RSKEW
Maximum Data Rate
Receiver Enable to Output ꢁigh
Receiver Enable to Output Low
Receiver Disable Time from ꢁigh
Receiver Disable Time from Low
t
t
Figure 7
Figure 7
Figure 7
Figure 7
50
50
50
50
RZꢁ
t
ns
RZL
ns
RꢁZ
t
ns
RLZ
Receiver Enable from Shutdown
to Output ꢁigh
t
RZꢁ
Figure 8
2200
ns
(SꢁDN)
4
_______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
SWITCHING CHARACTERISTICS—MAX13488E (continued)
(V
= +5V 5ꢃ, T = T
to T
, unless otherwise noted. Typical values are at V
= +5V and T = +25°C.)
CC A
CC
A
MIN
MAX
PARAMETER
SYMꢁOL
CONDITIONS
MIN
TYP
MAX
UNITS
Receiver Enable from Shutdown
to Output Low
t
RZL
(SꢁDN)
Figure 8
Figure 3
2200
ns
Receiver Enable Delay
Time to Shutdown
t
70
ns
ns
RED
t
50
340
700
SꢁDN
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 ꢂ that the driving device must see on the bus to disable its driver.
Note 3: The short-circuit output current applied to peaꢀ current just prior to foldbacꢀ current limiting. The short-circuit foldbacꢀ out-
put current applies during current limiting to allow a recovery from bus contention.
Typical Operating Characteristics
(V
= +5.0V, T = +25°C, unless otherwise noted.)
A
CC
OUTPUT CURRENT
vs. RECEIVER OUTPUT-HIGH VOLTAGE
OUTPUT CURRENT
vs. RECEIVER OUTPUT-LOW VOLTAGE
SUPPLY CURRENT vs. TEMPERATURE
4.0
35
28
21
14
7
60
50
40
30
20
10
0
NO LOAD
3.8
3.6
3.4
3.2
3.0
0
-40
-15
10
35
60
85
0
1
2
3
4
5
0
1
2
3
4
5
TEMPERATURE (°C)
OUTPUT-HIGH VOLTAGE (V)
OUTPUT-LOW VOLTAGE (V)
RECEIVER OUTPUT-LOW
VOLTAGE vs. TEMPERATURE
RECEIVER OUTPUT-HIGH VOLTAGE
vs. TEMPERATURE
DIFFERENTIAL OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
0.5
0.4
0.3
0.2
0.1
0
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
80
60
40
20
0
I = 1mA
O
I
= 1mA
O
-40
-15
10
35
60
85
-40
-15
10
35
60
85
0
1
2
3
4
5
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
_______________________________________________________________________________________
5
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Typical Operating Characteristics (continued)
(V
= +5.0V, T = +25°C, unless otherwise noted.)
CC
A
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
OUTPUT CURRENT
vs. TRANSMITTER OUTPUT-HIGH VOLTAGE
OUTPUT CURRENT
vs. TRANSMITTER OUTPUT-LOW VOLTAGE
3.0
120
100
80
60
40
20
0
120
100
80
60
40
20
0
R
= 54Ω
DIFF
2.5
2.0
1.5
1.0
0.5
0
-40
-15
10
35
60
85
-7 -6 -5 -4 -3 -2 -1
0
1
2
3
4
5
0
2
4
6
8
10
12
TEMPERATURE (C°)
OUTPUT-HIGH VOLTAGE (V)
OUTPUT-LOW VOLTAGE (V)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
SHUTDOWN CURRENT vs. TEMPERATURE
600
500
400
300
200
100
0
1000
800
600
400
200
0
10
9
8
7
6
5
4
3
2
1
0
R = 110Ω
L
R = 10kΩ
L
t
DPLH
t
DPLH
t
DPHL
t
DPHL
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
RECEIVER PROPAGATION vs. TEMPERATURE
(MAX13487E)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
DRIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
60
30
25
20
15
10
5
30
25
20
15
10
5
R = 10kΩ
L
R = 110Ω
L
45
t
RPHL
30
15
t
t
DPLH
DPLH
t
RPLH
t
DPHL
t
DPHL
0
0
0
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
6
_______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Typical Operating Characteristics (continued)
(V
= +5.0V, T = +25°C, unless otherwise noted.)
A
CC
RECEIVER PROPAGATION vs. TEMPERATURE
(MAX13488E)
40
DRIVER PROPAGATION (500kbps)
(MAX13487E)
DRIVER PROPAGATION (16Mbps)
(MAX13488E)
DI
2V/div
DI
2V/div
30
t
RPLH
20
10
t
RPHL
A-B
5V/div
A-B
5V/div
WAVEFORM INTENSITY: 68%
10ns/div
0
-40
-15
10
35
60
85
400ns/div
TEMPERATURE (°C)
DRIVING 16nF (19.2kbps)
RECEIVER PROPAGATION (16Mbps)
(MAX13488E)
(MAX13487E)
B
2V/div
DI
2V/div
A
2V/div
A-B
RO
5V/div
2V/div
10µs/div
10ns/div
DRIVING 16nF (19.2kbps)
(MAX13488E)
DRIVING 16nF (750kbps)
(MAX13488E)
DI
2V/div
DI
2V/div
A-B
5V/div
A-B
5V/div
10µs/div
400ns/div
_______________________________________________________________________________________
7
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Test Circuits and Waveforms
A
R
L
R
DIFF
2
A
B
DI
V
CC
V
ID
C
L
GND
V
OD
C
L
R
L
R
DIFF
V
OC
2
B
Figure 2. Driver-Timing Test Circuit
Figure 1. Driver DC Test Load
RE = V
f = 1MHz, t ≤ 3ns, t ≤ 3ns
LH HL
CC
V
CC
0
1.5V
1.5V
DI
1/2 V
O
t
t
DPHL
DPLH
B
A
V
O
1/2 V
RO
O
t
, t
DDD RED
(RO PULLED LOW)
O
V
= V(A) - V(B)
DIFF
V
O
90%
90%
V
DIFF
0
10%
10%
LH
-V
O
t
HL
t
Figure 3. Driver Propagation Delays
8
_______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Test Circuits and Waveforms (continued)
V
CC
1.5V
SHDN
0
t
DZL(SHDN)
A, B
V
500Ω
CC
2.3V
S
S
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
OUTPUT
UNDER TEST
1
2
V
OL
C
L
A, B
0
2.3V
t
DZH(SHDN)
Figure 4. Driver Enable and Disable Times
B
RECEIVER
OUTPUT
V
ID
R
ATE
A
Figure 5. Receiver-Propagation-Delay Test Circuit
f = 1MHz, t ≤ 3ns, t ≤ 3ns
LH
HL
1V
A
B
-1V
t
t
RPLH
RPHL
V
OH
RO
1.5V
1.5V
V
OL
t
=
t
- t
RSKEW | RPHL RPLH |
Figure 6. Receiver Propagation Delays
_______________________________________________________________________________________
9
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Test Circuits and Waveforms (continued)
V
CC
0
RE
1.5V
1.5V
t
, t
t
RZL(SHDN) RZL
RHZ
V
CC
0
V
V
+ 0.5V
+ 0.5V
OH
RO
RO
2.3V
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
V
CC
2.3V
OH
0
t
, t
t
RHZ
RZH(SHDN) RZH
DI = 0V
Figure 7. Receiver Enable and Disable Times
V
CC
0
1.5V
SHDN
t
RZL(SHDN)
V
V
CC
0
V
500Ω
CC
RO
RO
2.3V
S
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
1
2
RO
C
S
L
CC
0
2.3V
t
RZH(SHDN)
DI = 1
Figure 8. Receiver Enable Time from Shutdown
10 ______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Pin Description
PIN
NAME
FUNCTION
Receiver Output. When receiver is enabled and V(A) - V(ꢂ) > +200mV, RO is high. If V(A) - V(ꢂ)
< -200mV, RO is low.
1
RO
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).
2
3
RE
Shutdown. Drive SHDN high to let the device operate in normal operation. Drive SHDN low to put the part
in shutdown.
SHDN
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).
4
DI
5
6
7
8
GND
A
Ground
Noninverting Receiver Input and Noninverting Driver Output
Inverting Receiver Input and Inverting Driver Output
ꢂ
V
Positive Supply, V
= +5V 5ꢃ. ꢂypass V
to GND with a 0.1µF capacitor.
CC
CC
CC
Function Tables
TRANSMITTING
INPUTS
A-ꢁ > V
OUTPUTS
SHDN
DI
0
ACTION
Turn driver ON
A
ꢁ
DT
1
1
1
1
0
X
0
1
1
False
False
True
X
If driver was OFF, ꢀeep it OFF
If driver was ON, ꢀeep it ON
Turn driver OFF
ꢁIGꢁ IMPEDANCE
1
ꢁIGꢁ IMPEDANCE
0
1
1
ꢁIGꢁ IMPEDANCE
ꢁIGꢁ IMPEDANCE
X
X
SꢁUTDOWN
RECEIVING
INPUTS
OUTPUT
SHDN
RE
0
A-ꢁ
DRIVER STATE
RECEIVER STATE
RO
1
1
1
1
1
0
≥+200mV
≤-200mV
X
X
X
ON
ON
OFF
ON
ON
X
1
0
0
1
ON
OFF
OFF
X
ꢁIGꢁ IMPEDANCE
1
>+200mV
≤-200mV
X
1
1
0
X
SꢁUTDOWN
X = Don’t care, shutdown mode, driver, and receiver outputs are in high impedance.
______________________________________________________________________________________ 11
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
important factor when sizing these resistors is to guar-
Detailed Description
antee that the idle voltage on the bus (A-ꢂ) is greater
than 200mV in order to remain compatible with stan-
dard RS-485 receiver thresholds.
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 Hot-
Swap 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 500ꢀbps.
The MAX13488E driver slew rate is not limited, maꢀing
data throughput of up to 16Mbps possible.
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 trans-
ceiver has DE and RE inputs that are used to enable
and disable the driver and receiver. ꢁowever, 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.
AutoDirection Circuitry
Internal circuitry in the MAX13487E/MAX13488E, in
conjunction with an external pullup resistor on A and
pulldown resistor on ꢂ (see Typical Operation Circuit),
act to automatically disable or enable the driver and
receiver to ꢀeep 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 networꢀ is driving the bus.
Hot-Swap Capability
Hot-Swap Inputs
When circuit boards are inserted into a hot or powered
bacꢀ plane, differential disturbances to the data bus
can lead to data errors. Upon initial circuit-board inser-
tion, 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. Leaꢀage currents up to
10µA from the high-impedance state of the proces-
sor’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
The internal state machine has two inputs:
• DI
• The current state of A-ꢂ (determined by a dedicated
differential comparator)
The state machine also has two outputs:
cause coupling of V
or GND to the enable inputs.
• DRIVER_ENAꢂLE—Internal signal that enables and
disables the driver
CC
Without the hot-swap capability, these factors could
improperly enable the transceiver’s driver.
• RECEIVER_ENAꢂLE—Internal signal that is the
inverse of the DRIVER_ENAꢂLE signal, but it can be
overridden by an external pin
To overcome both these problems, two different pullup
switches (strong and weaꢀ) are turned on during the
power-up. When V
rises, an internal power-up signal
CC
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-ꢂ > 200mV). During each low-to-high transition
of DI, the driver stays enabled until (A-ꢂ) > V , and
DT
then disables the driver, letting the pullup/pulldown
resistors hold the A and ꢂ lines in the correct state.
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 weaꢀ pullup (100µA)
remains active to overcome leaꢀage on the pin. This
second weaꢀ pullup disappears as soon as the micro-
controller 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.
Pullup and Pulldown Resistors
The pullup and pulldown resistors on the A and ꢂ 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-ꢂ > 200mV) follow-
ing 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 terminat-
ed and how many nodes are on the bus. The most
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 V
ramps from zero, an internal 15µs timer turns
CC
12 ______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
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 V through a 5ꢀΩ resistor. M2
CC
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 leaꢀages
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.
V
CC
15µs
TIMER
TIMER
SR LATCH
Whenever V
drops below 1V, the hot-swap input is
CC
reset. DI has similar hot-swap circuitry.
15ꢀk 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
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 15ꢀV without damage. The ESD structures
withstand high ESD in all states: normal operation, shut-
down, and powered down. After an ESD event, the
MAX13487E/MAX13488E ꢀeep worꢀing without latchup
or damage.
5kΩ
RE
RE
(HOT SWAP)
100µA
500µA
M1
M2
V
CC
ESD protection can be tested in various ways. The
transmitter outputs and receiver inputs of the
MAX13487E/MAX13488E are characterized for protec-
tion to the following limits:
Figure 9. Simplified Structure of the Receiver Enable Pin (RE)
meet IEC 61000-4-2 without the need for additional
ESD-protection components.
•
•
15ꢀV using the ꢁuman ꢂody Model
The major difference between tests done using the
ꢁuman ꢂody Model and IEC 61000-4-2 is higher peaꢀ
current in IEC 61000-4-2 because series resistance is
lower in the IEC 61000-4-2 model. ꢁence, the ESD
withstand voltage measured to IEC 61000-4-2 is gener-
ally lower than that measured using the ꢁuman ꢂody
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.
15ꢀV using the Air Gap Discharge Method speci-
fied in 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 ꢁuman ꢂody Model, and Figure
10b 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 inter-
est, which is then discharged into the test device
through a 1.5ꢀΩ 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. Of course, all pins require this protec-
tion, not just RS-485 inputs and outputs.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD testing and
performance of finished equipment. ꢁowever, it does
not specifically refer to integrated circuits. The
MAX13487E/MAX13488E help you design equipment to
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.
______________________________________________________________________________________ 13
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
R
1MΩ
R
R
R
C
D
C
D
1500Ω
50MΩ TO 100MΩ
330Ω
DISCHARGE
RESISTANCE
DISCHARGE
RESISTANCE
CHARGE-CURRENT-
LIMIT RESISTOR
CHARGE-CURRENT-
LIMIT RESISTOR
HIGH-
VOLTAGE
DC
HIGH-
VOLTAGE
DC
DEVICE
UNDER
TEST
DEVICE
UNDER
TEST
C
s
150pF
STORAGE
CAPACITOR
C
s
100pF
STORAGE
CAPACITOR
SOURCE
SOURCE
Figure 10c. ICE 61000-4-2 ESD Test Model
Figure 10a. Human Body ESD Test Model
I
100%
90%
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
I
100%
90%
I
P
r
AMPS
36.8%
10%
0
10%
TIME
0
t = 0.7ns TO 1ns
r
t
RL
t
30ns
60ns
t
DL
CURRENT WAVEFORM
Figure 10d. IEC 61000-4-2 ESD Generator Current Waveform
Figure 10b. Human Body Current Waveform
Low-Power Shutdown Mode
Low-power shutdown mode is initiated by bringing
SHDN low. In shutdown, the devices draw a maximum
of 10µA of supply current.
Applications Information
128 Transceivers on the Bus
The standard RS-485 receiver input impedance is 12ꢀΩ
(1-unit load), and the standard driver can drive up to
32-unit loads. The MAX13487E/MAX13488E have a 1/4-
unit load receiver input impedance (48ꢀΩ), 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 32-
unit loads or fewer, can be connected to the line.
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 t
and t (see the Switching Character-
ZL
Zꢁ
istics section) assume the devices were not in a low-
power shutdown state. Enable times t and
Zꢁ(SꢁDN)
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 500ꢀbps.
t
assume the devices were in shutdown state. It
ZL(SꢁDN)
taꢀes drivers and receivers longer to become enabled
from low-power shutdown mode (t , t
)
Zꢁ(SꢁDN) ZL(SꢁDN)
than from driver/receiver-disable mode (t , t ).
Zꢁ ZL
Line Length
The RS-485/RS-422 standard covers line lengths up to
4000ft.
14 ______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
V
CC
V
CC
DI
D
DI
D
R
R
t
t
SHDN
SHDN
V
V
CC
CC
RO
RE
RO
RE
R
R
MAX13487E
MAX13488E
R
R
D
D
DI SHDN RO RE
DI
RO RE
SHDN
Figure 11. Typical Half-Duplex RS-485 Network
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 con-
tact bounce, better reliability, and better electrical isola-
tion. The MAX13487E/MAX13488E only require two
optocouplers to electrically isolate the transceiver.
Typical Applications
The MAX13487E/MAX13488E transceivers are
designed for half-duplex, bidirectional data communi-
cations on multipoint bus transmission lines. Figure 11
shows a typical networꢀ application. To minimize reflec-
tions, terminate the line at both ends in its characteristic
impedance, and ꢀeep stub lengths off the main line as
short as possible. The slew-rate-limited MAX13487E is
more tolerant of imperfect termination.
Isolated RS-485 Interface
An isolated RS-485 interface electrically isolates differ-
ent 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
Chip Information
PROCESS: ꢂiCMOS
______________________________________________________________________________________ 15
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Pin Configurations/Typical Application Circuit
V
SYS
V
RXD
ISO
V
CC
0.1µF
+
RO
RE
1
2
3
4
R
8
7
6
5
V
V
ISO
ISO
B
A
V
Rt
SYS
SHDN
DI
V
CC
D
GND
TXD
SO
16 ______________________________________________________________________________________
Half-Duplex RS-485-/RS-422-Compatible
Transceiver with AutoDirection Control
Pacꢀage Information
(The pacꢀage drawing(s) in this data sheet may not reflect the most current specifications. For the latest pacꢀage outline information,
go to www.maxim-ic.com/pacꢀages.)
INCHES
MILLIMETERS
DIM
A
MIN
MAX
0.069
0.010
0.019
0.010
MIN
1.35
0.10
0.35
0.19
MAX
1.75
0.25
0.49
0.25
0.053
0.004
0.014
0.007
N
A1
B
C
e
0.050 BSC
1.27 BSC
E
0.150
0.228
0.016
0.157
0.244
0.050
3.80
5.80
0.40
4.00
6.20
1.27
E
H
H
L
VARIATIONS:
INCHES
1
MILLIMETERS
DIM
D
MIN
MAX
0.197
0.344
0.394
MIN
4.80
8.55
9.80
MAX
5.00
N
8
MS012
AA
TOP VIEW
0.189
0.337
0.386
D
8.75 14
10.00 16
AB
D
AC
D
C
A
B
0∞-8∞
e
A1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0041
B
1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2007 Maxim Integrated Products
ꢂoblet
is a registered trademarꢀ of Maxim Integrated Products, Inc.
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