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MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
General Description
Benefits and Features
The MAX22506E ESD-protected RS-485/RS-422 transceiver is optimized for high-speed communication up to
50Mbps. This transceiver features integrated hot-swap
protection and a fail-safe receiver, ensuring a logic-high
on the receiver output when input signals are shorted or
open for longer than 10μs (typ). Additionally, a large receiver hysteresis improves noise rejection and signal integrity.
● High-Speed Operation over Long Distances
• Up to 50Mbps Data Rate
• High Receiver Sensitivity
• Wide Receiver Bandwidth
• Symmetrical Receiver Thresholds
The MAX22506E is designed to operate in harsh industrial
environments and is optimized for robust communication
in environments with high levels of electromagnetic interference (EMI).
The MAX22506E is available in an 8-pin SOIC and an
8-pin μMAX package. The transceiver operates over the
-40°C to +125°C temperature range.
Applications
●
●
●
●
●
Motion Control
Encoder Interfaces
Field Bus Networks
Industrial Control Systems
Backplane Busses
● Integrated Protection Increases Robustness
• -15V to +15V Common-Mode Range
• ±15kV ESD Protection (Human Body Model)
• ±7kV IEC 61000-4-2 Air-Gap ESD Protection
• ±6kV IEC 61000-4-2 Contact Discharge ESD
Protection
• Withstands Over ±4kV EFT
• Driver Outputs are Short-Circuit Protected
● Flexibility for Many Different Applications
• 3V to 5.5V Supply Range
• Low 5μA (max) Shutdown Current
• Available in 8-pin SOIC and μMAX Packages
• -40°C to +125°C Operating Temperature Range
Ordering Information appears at end of data sheet.
Simplified Block Diagram
VCC
RO
R
B
RE
DE
DI
SHUTDOWN
D
MAX22506E
GND
µMAX is a registered trademark of Maxim Integrated Products, Inc.
19-100995; Rev 1; 5/21
A
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Absolute Maximum Ratings
VCC........................................................................... -0.3V to +6V
RE, DE, DI ................................................................ -0.3V to +6V
RO .............................................................. -0.3V to (VCC + 0.3V)
A, B .......................................................................... -15V to +15V
Short-Circuit Duration (RO, A, B) to GND .................. Continuous
Continuous Power Dissipation (TA = +70°C)
8-Pin μMAX (derate 4.8mW/°C above +70°C) ........... 387.8mW
8-Pin SOIC (derate 7.4mW/°C above +70°C) ............588.2mW
Operating Temperature Range ..........................-40°C to +125°C
Junction Temperature ...................................................... +150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering 10s) ................................... +300°C
Reflow Temperature ........................................................ +270ºC
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.
Package Information
μMAX8
Package Code
U8+1
Outline Number
21-0036
Land Pattern Number
90-0092
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction to Ambient (θJA)
206.3°C/W
Junction to Case (θJC)
42°C/W
SOIC8
Package Code
S8+2C
Outline Number
21-0041
Land Pattern Number
90-0096
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction to Ambient (θJA)
136°C/W
Junction to Case (θJC)
38°C/W
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 thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a
four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/
thermal-tutorial.
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Maxim Integrated | 2
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Electrical Characteristics
(VCC = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DC ELECTRICAL CHARACTERISTICS / POWER
Supply Voltage
VCC
Supply Current
ICC
Shutdown Supply
Current
ISHDN
3.0
DE = high, RE = low, no load
4
DE = low, RE = high
5.5
V
5.6
mA
5
µA
DC ELECTRICAL CHARACTERISTICS / DRIVER
Differential Driver
Output
Change in Magnitude of
Differential Output
Voltage
Driver Common-Mode
Output Voltage
Change in Magnitude of
Common-Mode Voltage
VOD
ΔVOD
VOC
ΔVOC
Figure 1
RL = 54Ω
1.5
RL = 100Ω
2.0
V
RL = 54Ω, Figure 1 (Note 3)
RL = 54Ω, Figure 1
VCC / 2
RL = 100Ω or 54Ω, Figure 1 (Note 3)
Single-Ended Driver
Output High
VOH
A or B output, IOUT = -20mA
Single-Ended Driver
Output Low
VOL
A or B output, IOUT = +20mA
Differential Output
Capacitance
COD
DE = high, f = 4MHz
Driver Short-Circuit
Output Current
|IOST|
-15V ≤ VOUT ≤ +15V
0.2
V
3
V
0.2
V
2.2
V
0.8
50
V
pF
250
mA
DC ELECTRICAL CHARACTERISTICS / RECEIVER
Input Current (A and B)
IA,B
DE = low,
VCC = 0V or
3V ≤ VCC ≤ 5.5V
VIN = +12V
Differential Input
Capacitance
CA,B
Between A and B, f = 2MHz
Common-Mode Voltage
Range
VCM
VIN = -7V
+390
μA
-360
50
-15
pF
+15
V
Receiver DifferentialThreshold High
VTH_H
-15V ≤ VCM ≤ +15V
+50
+122
+200
mV
Receiver DifferentialThreshold Low
VTH_L
-15V ≤ VCM ≤ +15V
-200
-122
-50
mV
Receiver Input
Hysteresis
ΔVTH
VCM = 0V, time from last transition
is < tD_FS
VTH_FS
-15V ≤ VCM ≤ +15V, time from last
transition > tF_DS
Differential Input
Fail-Safe Level
250
-50
mV
+50
mV
DC ELECTRICAL CHARACTERISTICS / LOGIC INTERFACE (RE, RO, DE, DI)
Input-Voltage High
Input-Voltage Low
www.maximintegrated.com
VIH
VIL
DE, DI, RE
DE, DI, RE
3V ≤ VCC ≤ 5.5V
2/3 x
VCC
VCC = 5.25V
2.85
V
1/3 x
VCC
V
Maxim Integrated | 3
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Electrical Characteristics (continued)
(VCC = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
Input Current
Input Impedance on
First Transition
SYMBOL
IIN
RIN_FT
CONDITIONS
DE, DI, RE (after first transition)
MIN
TYP
-2
DE, RE
RO Output-High Voltage
VOH
RE = low, (VA - VB) > 200mV,
IOUT = -1mA
RO Output-Low Voltage
VOL
RE = low, (VA–VB) < -200mV,
IOUT = +1mA
Three-State Output
Current at Receiver
IOZR
RE = high, 0 ≤ VRO ≤ VCC
Thermal-Shutdown
Threshold
TSH
Temperature rising
Thermal-Shutdown
Hysteresis
TSH_HYS
MAX
UNITS
+2
μA
10
kΩ
VCC –
0.4
V
-1
0.4
V
+1
μA
PROTECTION
ESD Protection
(A and B Pins)
ESD Protection
(All Other Pins)
+160
°C
10
°C
Human Body Model
±15
IEC61000-4-2 Air Gap Discharge to GND
±7
IEC61000-4-2 Contact Discharge to GND
±6
Human Body Model
±2
kV
kV
AC ELECTRICAL CHARACTERISTICS / DRIVER (Note 4)
Driver Propagation
Delay
tDPLH
RL = 54Ω, CL = 50pF, Figure 2, Figure 3
32
tDPHL
RL = 54Ω, CL = 50pF, Figure 2, Figure 3
32
ns
Differential-Driver
Output Skew
tDSKEW
|tDPLH – tDPHL|, RL = 54Ω, CL = 50pF,
Figure 2, Figure 3 (Note 5)
1.2
ns
Driver DifferentialOutput Rise and Fall
Time
tHL, tLH
RL = 54Ω, CL = 50pF, Figure 3 (Note 5)
3
ns
Maximum Data Rate
DR
50
Mbps
Driver Enable to Output
High
tDZH
RL = 500Ω, CL = 50pF, Figure 4
32
ns
Driver Enable to Output
Low
tDZL
RL = 500Ω, CL = 50pF, Figure 5
32
ns
Driver Disable Time
from High
tDHZ
RL = 500Ω, CL = 50pF, Figure 4
32
ns
Driver Disable Time
from Low
tDLZ
RL = 500Ω, CL = 50pF, Figure 5
32
ns
Driver Enable from
Shutdown to Output
High
tDZH(SHDN)
RL = 1kΩ, CL = 15pF, Figure 4
100
µs
Driver Enable from
Shutdown to Output Low
tDZL(SHDN)
RL = 1kΩ, CL = 15pF, Figure 5
100
µs
800
ns
Time to Shutdown
www.maximintegrated.com
tSHDN
(Notes 6, 7)
50
Maxim Integrated | 4
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Electrical Characteristics (continued)
(VCC = 3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = 3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
AC ELECTRICAL CHARACTERISTICS / RECEIVER (Note 4)
Delay to Fail-Safe
Operation
tD_FS
Receiver Propagation
Delay
tRPLH,
tRPHL
Receiver Output Skew
tRSKEW
Maximum Data Rate
10
µs
CL = 15pF, Figures 6, 7
40
ns
|tRPHL - tRPLH|, CL= 15pF, Figures 6, 7
(Note 5)
2.5
ns
DR
50
Mbps
Receiver Enable to
Output High
tRZH
RL = 1kΩ, CL = 15pF, Figure 8
32
ns
Receiver Enable to
Output Low
tRZL
RL = 1kΩ, CL = 15pF, Figure 8
32
ns
Receiver Disable Time
from Low
tRLZ
RL = 1kΩ, CL = 15pF, Figure 8
32
ns
Receiver Disable Time
from High
tRHZ
RL = 1kΩ, CL = 15pF, Figure 8
32
ns
Receiver Enable from
Shutdown to Output
High
tRZH(SHDN)
RL = 1kΩ, CL = 15pF, Figure 8
100
μs
Receiver Enable from
Shutdown to Output Low
tRZL(SHDN)
RL = 1kΩ, CL = 15pF, Figure 8
100
μs
800
ns
Time to Shutdown
tSHDN
(Notes 6, 7)
50
Note 1: All devices are 100% production tested at TA = +25°C. Specifications for all temperature limits are guaranteed by design.
Note 2: All currents into the device are positive. All currents out of the device are negative. All voltages are referenced to the device
ground, unless otherwise noted.
Note 3: ΔVOD and ΔVOC are the changes in VOD and VOC, respectively, when the DI input changes state.
Note 4: Capacitive load includes test probe and fixture capacitance.
Note 5: Not production tested. Guaranteed by design.
Note 6: Shutdown is enabled by driving RE high and DE low. The device is guaranteed to have entered shutdown after tSHDN has
elapsed.
Note 7: Time to shutdown refers to the driver or receiver enable delay when the device has exited the initial hot-swap protect state and
is in normal operating mode.
A
VOD
B
RL
2
RL
2
VOC
Figure 1. Driver DC Test Load
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Maxim Integrated | 5
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
A
VCC
DE
DI
RL
VOD
CL
B
Figure 2. Driver Timing Test Circuit
DI
50%
VCC
50%
0
tDPLH
tDPHL
½ VOD
B
A
½ VOD
VOD
VOD = (VA - VB)
VOD
90%
90%
10%
10%
+VO
0
-VO
tHL
tLH
tDSKEW = |tDPLH - tDPHL|
Figure 3. Driver Propagation Delays
GND OR VCC
DI
DE
A
B
CL
RL
OUT
VCC
DE
tDZH, tDZH(SHDN)
1.5V
0.25V
GENERATOR
50Ω
OUT
1.5V
tDHZ
0V
VOH
0V
Figure 4. Driver Enable and Disable Times (tDZH, tDHZ)
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Maxim Integrated | 6
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
VCC
RL
GND OR VCC
DI
DE
A
B
OUT
CL
DE
tDZL, tDZL(SHDN)
VCC
1.5V
0V
tDLZ
GENERATOR
50Ω
1.5V
OUT
0.25V
VCC
VOL
Figure 5. Driver Enable and Disable Times (tDZL, tDLZ)
A
ATE
R
VID
RO
B
Figure 6. Receiver Propagation Delay Test Circuit
A
+1V
B
-1V
tRPHL
tRPLH
VOH
RO
50%
50%
VOL
tRSKEW = |tRPHL – tRPHL|
Figure 7. Receiver Propagation Delays
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Maxim Integrated | 7
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
S3
+1.5V
-1.5V
VIO
RO
R
RE
GENERATOR
VCC
RE
1.5V
0V
tRZH, tRZH(SHDN)
VCC
RO
2
1.5V
S1
S2
CL
15pF
VCC
50Ω
S1 OPEN
S2 CLOSED
S3 = +1.5V
VCC
RE
1.5V
VCC
RO
2
0V
0V
tRHZ
S1 OPEN
S2 CLOSED
S3 = +1.5V
1.5V
S1 CLOSED
S2 OPEN
S3 = -1.5V
VCC
VOL
VCC
RE
0V
S1 CLOSED
S2 OPEN
S3 = -1.5V
tRLZ
VCC
VOH
RO
0V
tRZL, tRZL(SHDN)
VOH
VCC
RE
RL
1kΩ
0.25V
RO
0V
0.25V
VOL
Figure 8. Receiver Enable and Disable Times
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Maxim Integrated | 8
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Typical Operating Characteristics
(VCC = 5V, 60Ω termination between the driver outputs, TA = 25°C, unless otherwise noted.)
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Maxim Integrated | 9
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Typical Operating Characteristics (continued)
(VCC = 5V, 60Ω termination between the driver outputs, TA = 25°C, unless otherwise noted.)
Pin Configuration
MAX22506E
TOP VIEW
RO
1
RE
2
DE
DI
+
8
VCC
7
B
3
6
A
4
5
GND
MAX22506E
SOIC
μMAX
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Maxim Integrated | 10
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Pin Description
PIN
NAME
1
RO
Receiver Output. See the Receiving Table for more information.
FUNCTION
2
RE
Receiver Enable. Pull RE high to disable the receiver and three-state RO. The device is in lowpower shutdown when RE = high and DE = low.
3
DE
Driver Output Enable. Force DE high to enable the driver. The device is in low-power shutdown
when RE = high and DE = low.
4
DI
Driver Input. See the Transmitting Table for more information.
5
GND
6
A
Noninverting Driver Output/Receiver Input
7
B
Inverting Driver Output/Receiver Input
8
VCC
Ground
Supply Input. Bypass VCC to ground with a 0.1μF ceramic capacitor as close to the device as
possible.
Function Tables
Transmitting Table
INPUTS
OUTPUTS
RE
DE
DI
A
B
X
1
1
1
0
X
1
0
0
1
0
0
X
High Impedance
High Impedance
1
0
X
Shutdown.
Driver outputs are high impedance
X = Don't care
Receiving Table
INPUTS
OUTPUTS
RE
DE
(VA - VB)
Time from Last
A-B Transition
0
X
≥ +200mV
Always
1
RO
0
X
-200mV < (VA - VB) < +200mV
< tD_FS
Indeterminate
RO is latched to previous value
0
X
-50mV < (VA - VB) < +50mV
> tD_FS
1
0
X
≤ -200mV
Always
0
0
X
Open/Shorted
> tD_FS
1
1
1
X
X
High Impedance
1
0
X
X
Shutdown.
RO is high impedance
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Maxim Integrated | 11
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Detailed Description
The MAX22506E ESD-protected RS-485/RS-422 transceiver is optimized for high-speed communications up to 50Mbps.
This transceiver features integrated hot-swap functionality to eliminate false transitions on the driver during power-up or
during a hot-plug event. This transceiver also feature fail-safe receiver inputs, guaranteeing a logic-high on the receiver
output when inputs are shorted or open for longer than 10µs (typ).
Receiver Threshold Voltages
The device receiver features a large threshold hysteresis of 250mV (typ) for increased differential noise rejection.
Additionally, the receiver features symmetrical threshold voltages. Symmetric thresholds have the advantage that
recovered data at the RO output does not have duty-cycle distortion. Typically, fail-safe receivers, which have unipolar
(non-symmetric) thresholds, show some duty-cycle distortion at high signal attenuation due to long cable lengths.
Fail-Safe Functionality
The MAX22506E features fail-safe receiver inputs, guaranteeing a logic-high on the receiver output (RO) when the
receiver inputs are shorted or open for longer than 10μs (typ). When the differential receiver input voltage is between
±50mV, or -50mV ≤ (VA - VB) ≤ +50mV, for more than 10μs (typ), RO is logic-high. For example, in the case of a
terminated bus with all transmitters disabled, the receiver differential input voltage is pulled to 0V by the termination
resistor, so -50mV ≤ (VA - VB) = 0V ≤ +50mV and RO is guaranteed to be a logic high after 10μs (typ).
Driver Single-Ended Operation
The driver outputs of the MAX22506E can be used in the standard differential operating mode or as single-ended outputs.
Because the driver outputs swing rail-to-rail, they can also be used as individual standard TTL or CMOS logic outputs.
Hot-Swap Capability
The DE and RE enable inputs feature hot-swap functionality. At each input there are two nMOS devices, M1 and M2
(Figure 9). When VCC ramps from zero, an internal 10μs timer turns on M2 and sets the SR latch, which also turns on
M1. Transistors M2 (a 500μA current sink) and M1 (a 100μA current sink) pull DE to GND through a 5kΩ resistor. M2 is
designed to pull DE to the disabled state against an external parasitic capacitance up to 100pF that can drive DE high.
After 10μs, the timer deactivates M2 while M1 remains on, holding DE low against three-state leakages that can drive DE
high. M1 remains on until an external source overcomes the required input current. At this time, the SR latch resets and
M1 turns off. When M1 turns off, DE reverts to a standard, high-impedance CMOS input. Whenever VCC drops below
1V, the hot-swap input is reset.
Note: Figure 9 shows a complementary circuit for RE that uses two pMOS devices to pull RE to VCC.
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Maxim Integrated | 12
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
VCC
10µs
TIMER
TIMER
5kΩ
DE
(HOT-SWAP)
DE
100µA
500µA
M1
M2
Figure 9. Simplified Structure of the Driver Enabled (DE) Pin
Driver Output Protection
Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. The first,
a current limit on the output stage, provides immediate protection against short-circuits over the whole common-mode
voltage range. The second, a thermal-shutdown circuit, forces the driver outputs into a high-impedance state if the die
temperature exceeds +160°C (typ).
Low-Power Shutdown Mode
The MAX22506E features a low-power shutdown mode to reduce supply current when the transceiver is not needed. Pull
the RE input high and the DE input low to put the device in low-power shutdown mode. If the inputs are in this state for at
least 800ns, the parts are guaranteed to enter shutdown. The MAX22506E draws 5μA (max) of supply current when the
device is in shutdown.
The RE and DE inputs can be driven simultaneously. The MAX22506E is guaranteed not to enter shutdown if RE is high
and DE is low for less than 50ns.
Integrated ESD Protection
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 MAX22506E have extra protection against static
electricity. The ESD structures withstand high ESD in all states: normal operation, shutdown, and powered down. After
an ESD event, the MAX22506E is able to keep working without latch-up or damage.
ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the MAX22506E are
characterized for protection to the following limits:
● ±15kV HBM
● ±7kV using the Air-Gap Discharge method specified in IEC 61000-4-2
● ±6kV using the Contact Discharge method specified in IEC 61000-4-2
Human Body Model (HBM)
Figure 10 shows the HBM test model, and Figure 11 shows the current waveform it generates when discharged into a
low-impedance state. This models consists of a 100pF capacitor charged to the ESD voltage of interest, which is then
discharged into a test device through a 1.5kΩ resistor.
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Maxim Integrated | 13
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
RC
1MW
CHARGE CURRENTLIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
CS
100pF
RD
1.5kW
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
Figure 10. Human Body ESD Test Model
IP
100%
90%
IR
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
36.8%
10%
0
0
tRL
TIME
tDL
Figure 11. Human Body Current Waveform
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 integrated ESD protection circuitry in the transceiver helps in designing
equipment to meet IEC 61000-4-2.
The major difference between tests done using the HBM and IEC 61000-4-2 models is the higher peak current in IEC
61000-4-2. This is due to the lower series resistance in the IEC 61000-4-2 model and typically results in the withstand
voltage measured to IEC 61000-4-2 being generally lower than that measured using the HBM.
Figure 12 shows the IEC 61000-4-2 model and Figure 13 shows the current waveform for the IEC 61000-4-2 ESD
Contact Discharge test.
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Maxim Integrated | 14
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
RC
RD
50MW TO 100MW
330W
CHARGE CURRENTLIMIT RESISTOR
HIGHVOLTAGE
DC
SOURCE
DISCHARGE
RESISTANCE
STORAGE
CAPACITOR
CS
150pF
DEVICE
UNDER
TEST
Figure 12. IEC 61000-4-2 ESD Test Model
IPEAK
I
100%
90%
10%
tR = 0.7ns to 1ns
t
30ns
60ns
Figure 13. IEC 61000-4-2 ESD Generator Current Waveform
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Maxim Integrated | 15
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Applications Information
Transceivers on the Bus
The A and B receiver inputs have an input current of 390μA (max) at 12V and -360μA (min) at -7V, respectively.
According to the RS-485 standard, the relative receiver input resistance can be calculated as 360μA/800μA = 0.45 unit
load (UL). Assuming a line terminated at both ends, up to 71 (= 32UL/0.45UL) MAX22506E transceivers can be used on
a multi-drop network. Note that this maximum number of nodes is calculated based on DC criteria only and does not take
into consideration signal integrity and transmission line effects at high data rates.
Transient Protection
Transient events that can occur in industrial environments include electrostatic discharge (ESD), surge events (e.g.,
lightning strikes), and electrical fast transient (EFT) or burst events. Surge pulses typically have a longer duration and
higher power-withstand requirements than EFT and ESD strikes. Test requirements and limits for ESD, surge, and burst
conditions are included in the IEC 61000-4-2, IEC 61000-4-4, and IEC 6100-4-5 standards.
External ESD Protection
The MAX22506E is internally protected against electrostatic discharge (ESD) events for the levels shown in the
Protection section of the Electrical Characteristics table. While this internal protection increases the robustness of the
device, additional external protection might be required to meet higher ESD limits or to protect against other high-voltage
transients in the final application.
Electrical Fast Transient (EFT) Events
The IEC 61000-4-4 standard outlines the voltage levels and duration of an electrical fast transient (EFT) or burst event.
EFT is typically a high-frequency, high-voltage burst that is coupled on to the RS-485 cable from external high-voltage
switching signals. For example, switching from nearby relays or motors can generate EFT on a RS-485 data line. Relative
to surge transient events, EFT bursts generate a small amount of power, but can corrupt data along the line.
To minimize the impact of EFT on signal lines, always use bypass capacitors soldered as close to the IC as possible.
Additionally, common-mode chokes and TVS diodes can help to clamp high-voltage transients. Capacitive or resistorcapacitor filters can also be added on the signal lines. Shielded cables, if available, also help to reduce interference from
EFT.
Surge Protection
Surge transient events can occur during lightning strikes, for example, and are characterized by the IEC 61000-4-5
standard. Surge events generate high energy, with high voltage peaks and large currents being driven to the driver
outputs and receiver inputs.
Per the IEC 61000-4-5 standard, surge pulses must be referenced to protective earth (PE). Isolate PE from the field
ground and connect a high-voltage capacitor and a high-voltage resistor between the field ground and PE. Figure 14
shows the current flow through the transceiver and PCB during a surge event. The MAX22506E survived 8/20μs surge
testing up to ±2kV/42Ω with a 1000pF high-voltage capacitor without the need for external TVS protection.
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Maxim Integrated | 16
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
MICROCONTROLLER/
UART
MAX22506E
B
B
RTERM
MAX22506E
A
A
GNDS
SHIELD
SURGE APPLIED
AT A
A,, REF TO PE
GND_F
HIGHVOLTAGE
Y-CAP
HIGHVOLTAGE
RESISTOR
PE
Figure 14. Surge Protection
Layout Guidelines
The MAX22506E is designed for robust communication in harsh industrial environments. Use the following guidelines for
layout to ensure optimum performance:
●
●
●
●
Place the bypass capacitor as close to the VCC pin as possible
Use supply and ground planes to reduce trace inductance.
Place external protection (resistors, capacitors, diodes) as close to the device as possible.
Design protection components directly in the path of the driver output and receiver input signals.
Additionally, pull ground planes away from the RS-485/RS-422 data lines when operating at high data rates to reduce
capacitive coupling that can slow edge rates.
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Maxim Integrated | 17
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Typical Application Circuits
Half Duplex Point-to-Point Network
3.3V
3.3V
3.3V
0.1µF
0.1µF
VCC
VCC
RE
RE
MICROCONTROLLER
RO
R
DE
DI
B
B
A
A
RO
R
DE
D
DI
D
MAX22506E
MAX22506E
GND
GND
Ordering Information
PIN-PACKAGE
PACKAGE
CODE
SOIC8
S8+2C
MAX22506EASA+T
SOIC8
S8+2C
MAX22506EAUA+
μMAX8
U8+1
MAX22506EAUA+T
μMAX8
U8+1
PART
MAX22506EASA+
+ Denotes lead (Pb)-free/RoHS compliance.
T = Tape and reel.
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Maxim Integrated | 18
MAX22506E
50Mbps Half-Duplex
RS-485/RS-422 Transceiver with
High EFT Immunity
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
1/21
Release for Market Intro
1
5/21
Updated the General Description, Figure 3, Layout Guidelines, and removed the
future product designation from MAX22506EAUA+ and MAX22506EAUA+T in the
Ordering Information table
DESCRIPTION
—
1, 6, 17, 18
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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.
© 2021 Maxim Integrated Products, Inc.
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