Maxim MAX3443EEPA ±60v fault-protected, 10mbps, fail-safe rs-485 transceiver with â±15kv esd protection Datasheet

19-2441; Rev 0; 4/02
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
Applications
Features
♦ ±60V Fault Protection
♦ ±15kV ESD Protection
♦ Guaranteed 10Mbps Data Rate
♦ Allows Up to 128 Transceivers on the Bus
♦ -7V to +12V Common-Mode Input Range
♦ True Fail-Safe Receiver Inputs
♦ Hot-Swap Inputs for Telecom Applications
♦ Automotive Temperature Range (-40°C to +125°C)
♦ Industry-Standard Pinout
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX3443ECSA
0°C to +70°C
8 SO
MAX3443ECPA
0°C to +70°C
8 PDIP
Industrial Networks
MAX3443EESA
-40°C to +85°C
8 SO
Telecommunication Systems
MAX3443EEPA
-40°C to +85°C
8 PDIP
Automotive Applications
MAX3443EASA
-40°C to +125°C
8 SO
HVAC Controls
MAX3443EAPA
-40°C to +125°C
8 PDIP
RS-422/RS-485 Communications
Pin Configuration and Typical Operating Circuit
TOP VIEW
MAX3443E
R
1
8
VCC
RO
RE 2
7
B
RE 2
DE
3
6
A
DE
3
DI
4
5
GND
DI
4
RO
1
D
DIP/SO
R
D
8 VCC
7 B
Rt
6
A
5 GND
DE
D
DI
B
Rt
A
RO
R
RE
________________________________________________________________ Maxim Integrated Products
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.
1
MAX3443E
General Description
The MAX3443E fault-protected RS-485/RS-422 transceiver features ±60V protection from signal faults on communication bus lines. Each device contains one differential
line driver with three-state output, and one differential line
receiver with three-state input. The 1/4-unit-load receiver
input impedance allows up to 128 transceivers on a single bus. The device operates from a 5V supply at data
rates up to 10Mbps. True fail-safe inputs guarantee a
logic-high receiver output when the receiver inputs are
open, shorted, or connected to an idle data line.
Hot-swap circuitry eliminates false transitions on the
data cable during circuit initialization or connection to a
live backplane. Short-circuit current limiting and thermal
shutdown circuitry protect the driver against excessive
power dissipation, and integrated ±15kV ESD protection eliminates costly external protection devices.
The MAX3443E is available in 8-pin SO and PDIP packages, and is specified over commercial, industrial, and
automotive temperature ranges.
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
ABSOLUTE MAXIMUM RATINGS
All Voltages Referenced with Respect to GND
VCC ........................................................................................+7V
RE, DE, DI...................................................-0.3V to (VCC + 0.3V)
A, B (Note 1) ........................................................................±60V
RO ..............................................................-0.3V to (VCC + 0.3V)
Continuous Power Dissipation (TA = +70°C)
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
8-Pin PDIP (derate 9.09mW/°C above +70°C).............727mW
Operating Temperature Ranges
MAX3443EC_ _ ..................................................0°C to +70°C
MAX3443EE_ _ ...............................................-40°C to +85°C
MAX3443EA_ _ .............................................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Short-Circuit Duration (RO, A, B) ...............................Continuous
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: A, B must be terminated with 54Ω or 100Ω to guarantee ±60V fault protection.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +4.75V to +5.25V, 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
Differential Driver Output
Change in Magnitude of
Differential Output Voltage
Driver Common-Mode Output
Voltage
Change In Magnitude of
Common-Mode Voltage
VOD
∆VOD
VOC
∆VOC
Figure 1, RL = 50Ω
2.0
VCC
Figure 1, RL = 27Ω
1.5
VCC
Figure 1, RL = 50Ω or 27Ω (Note 2)
Figure 1, RL = 50Ω or 27Ω
VCC / 2
Figure 1, RL = 50Ω or 27Ω (Note 2)
V
0.2
V
3
V
0.2
V
DRIVER LOGIC
Driver Input High Voltage
VDIH
2.0
V
Driver Input Low Voltage
VDIL
0.8
V
Driver Input Current
IDIN
±2
µA
Driver Output Fault Current
IOFC
VA, B = ±60V, RL = 54Ω
±6
mA
Driver Short-Circuit Output
Current
IOSD
-7V ≤ VOUT ≤ +12V
(Note 3)
±350
mA
Driver Short-Circuit Foldback
Output Current
IOSDF
-7V ≤ VOUT ≤ +12V
(Note 3)
±25
mA
RECEIVER
Input Current
IA,B
A, B
DE = GND, VCC = GND,
VA, B = +12V
250
VA, B = -7V
-150
VA, B = ±60V
Receiver Differential Threshold
Voltage
Receiver Input Hysteresis
2
VTH
∆VTH
-7V ≤ VCM ≤ +12V
-200
25
_______________________________________________________________________________________
µA
±6
mA
-50
mV
mV
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
MAX3443E
DC ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
RECEIVER LOGIC
Output High Voltage
VOH
Figure 2, IOH = -1.6mA
Output Low Voltage
VOL
Figure 2, IOL = 1mA
VCC - 0.6
0.4
V
V
Three-State Output Current at
Receiver
IOZR
0 ≤ VA, B ≤ VCC
±1
µA
Receiver Input Resistance
RIN
-7V ≤ VCM ≤ +12V
Receiver Output Short-Circuit
Current
IOSR
0 ≤ VRO ≤ VCC
VCIH
DE, RE
48
kΩ
±95
mA
CONTROL
Control Input High Voltage
2.0
V
Input Current DE Current Latch
During First DE Rising Edge
90
µA
Input Current RE Current Latch
During First RE Falling Edge
90
µA
PROTECTION SPECIFICATIONS
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
A, B
RSOURCE = 0, RL = 54Ω
Overvoltage Protection
ESD Protection
A, B
MIN
TYP
MAX
±60
UNITS
V
IEC 1000-4-2 Air-Gap
Discharge
±2
IEC 1000-4-2 Contact
Discharge
±8
Human Body Model
±15
kV
SUPPLY CURRENT
Normal Operation
IQ
No load, DI = VCC or GND, RE = GND,
DE = VCC
10
mA
Supply Current in Shutdown
Mode
ISHDN
DE = GND, RE = VCC
10
µA
Supply Current with Output
Shorted with ±60V
ISHRT
DE = GND, RE = GND, output in three-state
±15
mA
_______________________________________________________________________________________
3
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
SWITCHING CHARACTERISTICS (DRIVER)
(VCC = +4.75V to +5.25V, 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 Propagation Delay
tPLHA,
tPLHB
Figure 3, RL = 27Ω, CL = 50pF
60
ns
Driver Differential Propagation
Delay
tDPLH,
tDPHL
Figure 4, RL = 54Ω, CL = 50pF
60
ns
tLH,
tHL
Figure 4, RL = 54Ω, CL = 50pF
25
ns
RL = 54Ω, CL = 50pF,
tSKEWAB = |tPLHA - tPHLB|,
tSKEWBA = |tPLHB - tPHLA|
10
ns
RL = 54Ω, CL = 50pF,
tDSKEW = |tDPLH - tDPHL|
10
ns
Driver Differential Output
Transition Time
Driver Output Skew
Differential Driver Output Skew
tSKEWAB,
tSKEWBA
tDSKEW
Maximum Data Rate
fMAX
Driver Enable Time to Output
High
tPDZH
Figure 5, RL = 500Ω, CL = 50pF
1200
ns
Driver Disable Time from Output
High
tPDHZ
Figure 5, RL = 500Ω, CL = 50pF
1200
ns
Driver Wake Time from Shutdown
to Output High
tPDHS
Figure 5, RL = 500Ω, CL = 50pF
4.2
µs
Driver Enable Time to
Output Low
tPDZL
Figure 6, RL = 500Ω, CL = 50pF
1200
ns
Driver Disable Time from Output
Low
tPDLZ
Figure 6, RL = 500Ω, CL = 50pF
1200
ns
Driver Wake Time from Shutdown
to Output Low
tPDLS
Figure 6, RL = 500Ω, CL = 50pF
4.2
µs
Time to Shutdown
tSHDN
RL = 500Ω, CL = 50pF
800
ns
4
10
_______________________________________________________________________________________
Mbps
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
(VCC = +4.75V to +5.25V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Receiver Propagation Delay
tRPLH,
tRPHL
Figure 7, CL = 20pF,
VID = 2V, VCM = 0
75
ns
Receiver Output Skew
tRSKEW
CL = 20pF,
tRSKEW = |tRPLH - tRPHL|
15
ns
Receiver Enable Time to Output
High
tRPZH
Figure 8, RL = 1kΩ, CL = 20pF
400
ns
Receiver Disable Time from
Output High
tRPHZ
Figure 8, RL = 1kΩ, CL = 20pF
400
ns
Receiver Wake Time from
Shutdown to Output High
tRPSH
Figure 8, RL = 1kΩ, CL= 20pF
4.2
µs
Receiver Enable Time to Output
Low
tRPZL
Figure 8, RL = 1kΩ, CL = 20pF
400
ns
Receiver Disable Time from
Output Low
tRPLZ
Figure 8, RL = 1kΩ, CL= 20pF
400
ns
Receiver Wake Time from
Shutdown to Output Low
tRPSL
Figure 8, RL = 1kΩ, CL= 20pF
4.2
µs
800
ns
Time to Shutdown
Note 2: ∆VOD and ∆VOC are the changes in VOD and VOC, respectively, when the DI input changes state.
Note 3: 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 recovery from bus contention.
Typical Operating Characteristics
(VCC = +5V, TA = +25°C, unless otherwise noted.)
4
DE = RE = GND
3
2
1
0.1
1
40
MAX3443E toc03
DE = GND, RE = VCC
SUPPLY CURRENT (nA)
SUPPLY CURRENT (mA)
5
10
RECEIVER OUTPUT CURRENT
vs. OUTPUT LOW VOLTAGE
RECEIVER OUTPUT CURRENT (mA)
DE = VCC, RE = GND
MAX3443E toc01
6
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX3443E toc02
NO-LOAD SUPPLY CURRENT
vs. TEMPERATURE
35
30
25
20
15
10
5
0
0
0.01
-40 -25 -10 5 20 35 50 65 80 95 110 125
-40 -25 -10 5 20 35 50 65 80 95 110 125
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT LOW VOLTAGE (V)
_______________________________________________________________________________________
5
MAX3443E
SWITCHING CHARACTERISTICS (RECEIVER)
Typical Operating Characteristics (continued)
(VCC = +5V, TA = +25°C, unless otherwise noted.)
RECEIVER OUTPUT CURRENT vs.
OUTPUT HIGH VOLTAGE
25
20
15
10
5
4.0
VOH, IOUT = +10mA
3.5
3.0
2.5
2.0
1.5
VOL, IOUT = -10mA
1.0
-40 -25 -10 5 20 35 50 65 80 95 110 125
OUTPUT HIGH VOLTAGE (V)
TEMPERATURE (°C)
DIFFERENTIAL OUTPUT VOLTAGE vs.
TEMPERATURE
2.5
2.0
RL = 54Ω
1.5
1.0
30
20
0
0.5
1.5
1.0
MAX3443E toc08
1600
1200
0.5
RL = 54Ω
800
400
0
-400
-800
-1600
2.0
2.5
3.0
3.5
DIFFERENTIAL OUTPUT VOLTAGE (VA - VB) (V)
-1200
0
6
40
2000
A, B CURRENT (µA)
RL = 100Ω
50
A, B CURRENT vs.
A, B VOLTAGE (TO GROUND)
MAX3443E toc07
DIFFERENTIAL OUTPUT VOLTAGE (V)
3.0
60
0
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
3.5
70
10
0.5
0
80
MAX3443E toc06
MAX3443E toc05
4.5
DRIVER OUTPUT CURRENT (mA)
30
5.0
RECEIVER OUTPUT VOLTAGE (V)
35
DRIVER OUTPUT CURRENT vs.
DIFFERENTIAL OUTPUT VOLTAGE
RECEIVER OUTPUT VOLTAGE vs.
TEMPERATURE
MAX3443E toc04
40
RECEIVER OUTPUT CURRENT (mA)
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
DE = RE = GND
-2000
-40 -25 -10 5 20 35 50 65 80 95 110 125
-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60
TEMPERATURE (°C)
A, B VOLTAGE (V)
_______________________________________________________________________________________
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
RL
2
A
DI
VOD
D
B
RL
VCC
VOC
2
Figure 1. Driver VOD and VCC
A
VID
RO
R
B
0
VOL
VOH
IOL
(+)
IOH
(-)
Figure 2. Receiver VOH and VOL
3V
VOM
DI
1.5V
1.5V
RL = 27Ω
A
DI
tPLHA
OUT
D
GENERATOR
(NOTE 4)
0
S1
tPHLA
VOH
B
50Ω
CL = 50pF
(NOTE 5)
VCC
VOM =
VOM
A
VOM
VOL
tPHLB
VOH + VOL
≈ 1.5V
2
tPLHB
VOH
B
VOM
VOM
VOL
Figure 3. Driver Propagation Times
3V
A
DI
D
GENERATOR
(NOTE 4)
0
RL =
54Ω
B
1.5V
1.5V
DI
CL
OUT
tDPHL
tDPLH
≈ 2.0V
50Ω
90%
VCC
CL
(A–B)
50%
10%
90%
50%
10%
CL = 50pF (NOTE 5)
tLH
≈ -2.0V
tHL
Figure 4. Driver Differential Output Delay and Transition Times
_______________________________________________________________________________________
7
MAX3443E
Test Circuits and Waveforms
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
MAX3443E
Test Circuits and Waveforms (continued)
A
DI
0 OR 3V
3V
S1
A, B
D
B
DE
GENERATOR
(NOTE 4)
DE
RL = 500W
CL = 50pF
(NOTE 5)
1.5V
1.5V
tPDZH
0
tPDHS
tPDHZ
50W
0.25V
A, B
VOM =
VOH + VOL
2
VOH
VOM
» 1.5V
0
Figure 5. Driver Enable and Disable Times
VCC
3V
A
DI
0 OR 3V
RL = 500Ω
S1
A, B
D
1.5V
1.5V
tPDZL
DE
0
tPDLS
tPDLZ
B
DE
GENERATOR
(NOTE 4)
CL = 50pF
(NOTE 5)
VCC
A, B
VOM
50Ω
0.25V
VOL
Figure 6. Driver Enable and Disable Times
3.0V
A
GENERATOR
(NOTE 4)
VID
50W
R
B
RO
(A–B)
1.5V
1.5V
CL = 20pF
(NOTE 5)
0
tRPLH
tRPHL
VCC
1.5V
RO
VOM
VOM
0
Figure 7. Receiver Propagation Delay
8
_______________________________________________________________________________________
0
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
S1
S3
1.5V
1kW
A
-1.5V
VID
R
RO
VCC
S2
B
CL = 20pF
(NOTE 5)
GENERATOR
(NOTE 4)
50W
3V
RE
1.5V
0
3V
S1 OPEN
S2 CLOSED
S3 = 1.5V
RE
1.5V
0
tRPZH
tRPSH
tRPZL
tRPSL
VOH
RO
VCC
RO
1.5V
1.5V
0
VOL
3V
RE
S1 CLOSED
S2 OPEN
S3 = -1.5V
1.5V
0
3V
S1 OPEN
S2 CLOSED
S3 = 1.5V
RE
1.5V
0
S1 CLOSED
S2 OPEN
S3 = -1.5V
tRPHZ
RO
tRPLZ
VOH
0.5V
RO
VCC
0.5V
0
VOL
Figure 8. Receiver Enable and Disable Times
Note 4: The input pulse is supplied by a generator with the following characteristics: f = 5MHz, 50% duty cycle; tr ≤ 6ns; Z0 = 50Ω.
Note 5: CL includes probe and stray capacitance.
Pin Description
PIN
NAME
1
RO
Receiver Output. If RE = low and (A–B) ≥ -50mV, RO = high; if (A–B) ≤ -200mV, RO = low.
FUNCTION
2
RE
Receiver Output Enable. Pull RE low to enable RO.
3
DE
Driver Output Enable. Force DE high to enable driver. Pull DE low to three-state the driver output. Drive RE
high and pull DE low to enter low-power shutdown mode.
4
DI
Driver Input. A logic low on DI forces the noninverting output low and the inverting output high. A logic high
on DI forces the noninverting output high and the inverting output low.
5
GND
6
A
Noninverting Receiver Input/Driver Output with Integrated ±15kV ESD Protection
7
B
Inverting Receiver Input/Driver Output with Integrated ±15kV ESD Protection
8
VCC
Ground
Positive Supply, VCC = +4.75V to +5.25V
_______________________________________________________________________________________
9
MAX3443E
Test Circuits and Waveforms (continued)
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
Function Tables
MAX3443E (RS-485/RS-422)
MAX3443E (RS-485/RS-422)
RECEIVING
TRANSMITTING
INPUTS
INPUTS
OUTPUTS
OUTPUT
RE
DE
DI
A
B
RE
DE
(A-B)
RO
0
0
X
High-Z
High-Z
0
X
≥0.2V
1
0
1
0
0
1
0
X
≤-0.2V
0
0
1
1
1
0
0
X
Open/Shorted
1
1
0
X
Shutdown
Shutdown
1
1
X
High-Z
1
1
0
0
1
0
X
Shutdown
1
1
1
1
0
1
X = Don’t care.
X = Don’t care.
Detailed Description
Driver
The driver accepts a single-ended, logic-level input
(DI) and transfers it to a differential, RS-485/RS-422
level output (A and B). Driving DE high enables the driver, while pulling DE low places the driver outputs (A
and B) into a high-impedance state (see the transmitting function table).
Receiver
The receiver accepts a differential, RS-485/RS-422
level input (A and B), and transfers it to a single-ended,
logic-level output (RO). Pulling RE low enables the
receiver, while driving RE high places the receiver
inputs (A and B) into a high-impedance state (see the
receiving function table).
Low-Power Shutdown
Force DE low and RE high to shut down the MAX3443E.
A time delay of 50ns prevents the device from accidentally entering shutdown due to logic skews when switching between transmit and receive modes. Holding DE
low and RE high for at least 800ns guarantees that the
MAX3443E enters shutdown. In shutdown, the device
consumes a maximum of 10µA supply current.
±60V Fault Protection
The driver outputs/receiver inputs of RS-485 devices in
industrial network applications often experience voltage
faults resulting from shorts to the power bus that
exceed the -7V to +12V range specified in the EIA/TIA485 standard. In these applications, ordinary RS-485
devices (typical absolute maximum -8V to +12.5V)
require costly external protection devices. To reduce
system complexity and eliminate this need for external
protection, the driver outputs/receiver inputs of the
MAX3443E withstand voltage faults up to ±60V with
10
respect to ground without damage. Protection is guaranteed regardless of whether the device is active, shut
down, or without power.
True Fail-Safe
The MAX3443E uses a -50mV to -200mV differential
input threshold to ensure true fail-safe receiver inputs.
This threshold guarantees the receiver output is a logic
high for shorted, open, or idle data lines. The -50mV to
-200mV threshold complies with the ±200mV threshold
specified in the EIA/TIA-485 standard.
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against ESD
encountered during handling and assembly. The
MAX3443E receiver inputs/driver outputs (A, B) have
extra protection against static electricity found in normal operation. Maxim’s engineers developed state-ofthe-art structures to protect these pins against ±15kV
ESD without damage. After an ESD event, the
MAX3443E continues working without latchup.
ESD protection can be tested in several ways. The
receiver inputs are characterized for protection to the
following:
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method specified
in IEC 1000-4-2 (formerly IEC 801-2)
• ±15kV using the Air-Gap Discharge method specified in IEC 1000-4-2 (formerly IEC 801-2)
ESD Test Conditions
ESD performance depends on a number of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
______________________________________________________________________________________
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
CHARGE-CURRENTLIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
IP 100%
90%
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
DEVICE
UNDER
TEST
36.8%
10%
0
0
TIME
tRL
tDL
CURRENT WAVEFORM
Figure 9a. Human Body ESD Test Model
Figure 9b. Human Body Model Current Waveform
Human Body Model
Figure 9a shows the Human Body Model, and Figure
9b 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 device through a
1.5kΩ resistor.
Body Model. Figure 10b shows the current waveform for
the ±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge
test. The Air-Gap test involves approaching the device
with a charge probe. The Contact Discharge method
connects the probe to the device before the probe is
energized.
IEC 1000-4-2
Since January 1996, all equipment manufactured and/or
sold in the European community has been required to
meet the stringent IEC 1000-4-2 specification. The IEC
1000-4-2 standard covers ESD testing and performance
of finished equipment; it does not specifically refer to integrated circuits. The MAX3443E helps you design equipment that meets Level 4 (the highest level) of IEC
1000-4-2, without additional ESD-protection components.
The main difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2. Because series resistance is
lower in the IEC 1000-4-2 ESD test model (Figure 10a),
the ESD withstand voltage measured to this standard is
generally lower than that measured using the Human
CHARGE-CURRENTLIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
Cs
150pF
Driver Output Protection
Two mechanisms prevent excessive output current and
power dissipation caused by faults, or bus contention.
The first, a foldback current limit on the driver output
stage, provides immediate protection against short circuits over the whole common-mode voltage range. The
second, a thermal shutdown circuit, forces the driver
I
100%
90%
RD
330Ω
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
IPEAK
RC
50MΩ TO 100MΩ
Machine Model
The Machine Model for ESD testing uses a 200pF storage capacitor and zero-discharge resistance. It mimics
the stress caused by handling during manufacturing
and assembly. All pins (not just RS-485 inputs) require
this protection during manufacturing. Therefore, the
Machine Model is less relevant to the I/O ports than are
the Human Body Model and IEC 1000-4-2.
DEVICE
UNDER
TEST
10%
tr = 0.7ns TO 1ns
t
30ns
60ns
Figure 10a. IEC 1000-4-2 ESD Test Model
Figure 10b. IEC 1000-4-2 ESD Generator Current Waveform
______________________________________________________________________________________
11
MAX3443E
RD
1.5kW
RC
1MW
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
outputs into a high-impedance state if the die temperature exceeds +160°C. Normal operation resumes when
the die temperature cools to +140°C, resulting in a
pulsed output during continuous short-circuit conditions.
VCC
15µs
Hot-Swap Capability
Hot-Swap Inputs
Inserting circuit boards into a hot, or powered, backplane may cause voltage transients on DE, RE, and
receiver inputs A and B that can lead to data errors. For
example, upon initial circuit board insertion, the processor undergoes a power-up sequence. During this period, the high-impedance state of the output drivers
makes them unable to drive the MAX3443E enable
inputs (DE, RE) to a defined logic level. Meanwhile,
leakage currents up to 10µA from the high-impedance
output, or capacitively coupled noise from VCC or GND,
could cause an input to drift to an incorrect logic state.
To prevent such a condition from occurring, the
MAX3443E features hot-swap input circuitry on DE and
RE to safeguard against unwanted driver activation
during hot-swap situations. When VCC rises, an internal
pulldown (or pullup for RE) circuit holds DE low for at
least 10µs, and until the current into DE exceeds
200µA. After the initial power-up sequence, the pulldown circuit becomes transparent, resetting the hotswap tolerable input.
Hot-Swap Input Circuitry
At the driver enable input (DE), there are two NMOS
devices, M1 and M2 (Figure 11). When VCC ramps from
zero, an internal 15µs timer turns on M2 and sets the
SR latch, which also turns on M1. Transistors M2, a
2mA current sink, and M1, a 100µA current sink, pull
DE to GND through a 5.6kΩ resistor. M2 pulls DE to the
disabled state against an external parasitic capacitance up to 100pF that may drive DE high. After 15µs,
the timer deactivates M2 while M1 remains on, holding
DE low against three-state leakage currents that may
drive DE high. M1 remains on until an external current
source overcomes the required input current. At this
time, the SR latch resets M1 and turns off. When M1
turns off, DE reverts to a standard, high-impedance
CMOS input. Whenever V CC drops below +1V, the
input is reset.
A complimentary circuit for RE utilizes two PMOS
devices to pull RE to VCC.
12
TIMER
TIMER
DE
(HOT SWAP)
5.6kΩ
100µA
M1
2mA
M2
Figure 11. Simplified Structure of the Driver Enable Pin (DE)
Applications Information
128 Transceivers on the Bus
The MAX3443E 1/4-unit-load receiver input impedance
(48kΩ) allows up to 128 transceivers connected in parallel on one communication line. Connect any combination of these devices, and/or other RS-485 devices, for
a maximum of 32 unit loads to the line.
RS-485 Applications
The MAX3443E transceiver provides bidirectional data
communications on multipoint bus transmission lines.
Figure 12 shows a typical network applications circuit.
The RS-485 standard covers line lengths up to 4000ft.
To minimize reflections, and reduce data errors, terminate the signal line at both ends in its characteristic
impedance, and keep stub lengths off the main line as
short as possible.
J1708 Applications
To configure the MAX3443E in a J1708 application, connect DI and RE to GND. Connect the signal to be transmitted to DE through an inverter. At each transceiver,
terminate the bus with the load circuit (shown in Figure
13). When all transceivers are idle in this configuration,
all receivers output a logic high because of the pullup
resistor on A and pulldown resistor on B. Since RE is
connected to GND, all transmitters on the bus listen at
______________________________________________________________________________________
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
DI
MAX3443E
120Ω
120Ω
DE
B
B
D
D
DI
DE
A
RO
B
A
B
A
A
R
R
RO
RE
RE
R
R
D
D
MAX3443E
DI
DE
RO RE
DI
DE
RO RE
Figure 12. MAX3443E Typical RS-485 Network
all times. Incoming data on DE enables the driver,
which pulls the line low and causes all receivers to output a logic low.
Chip Information
TRANSISTOR COUNT: 310
PROCESS: BiCMOS
VCC
DE
Tx
R1
4.7kW
DI
B
D
R3
47W
C1
2.2nF
MAX3443E
A
Rx
RO
R
J1708 BUS
C2
2.2nF
R4
47W
R2
4.7kW
RE
Figure 13. J1708 Application Circuit
______________________________________________________________________________________
13
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
SOICN.EPS
MAX3443E
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
14
______________________________________________________________________________________
±60V Fault-Protected, 10Mbps, Fail-Safe
RS-485 Transceiver with ±15kV ESD Protection
PDIPN.EPS
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 ____________________ 15
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX3443E
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
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