Ordering Information appears at end of data sheet.
19-6925; Rev 3; 4/15
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
General Description
The MAX31912 industrial interface serializer translates,
conditions, and serializes the 24V digital output of sensors
and switches used in industrial, process, and building
automation to 5V CMOS-compatible signals required
by microcontrollers. It provides the front-end interface
circuit of a programmable logic controller (PLC) digital
input module.
The device features integrated current limiting, lowpass
filtering, and channel serialization. Input current limiting
allows a significant reduction in power consumed from
the field voltage supply as compared to traditional dis-
crete resistor-divider implementations. Selectable on-chip
lowpass filters allow flexible debouncing and filtering of
sensor outputs based on the application.
On-chip serialization allows a drastic reduction in the
number of optocouplers used for isolation. The device
serializer is stackable so that any number of input channels
can be serialized and output through only one SPI-
compatible port. This reduces the number of optocouplers
needed to only three, regardless of the number of input
channels.
For enhanced robustness with respect to high-frequency
noise and fast electrical transients, a multibit CRC code
is generated and transmitted through the SPI port for
each 8 bits of data. The on-chip 5V voltage regulator can
be used to power external optocouplers, digital isolators, or
other external 5V circuitry. Field-side LED drivers recycle
the current from the eight inputs to provide visual input
status indication without any additional current or power
consumption.
The MAX31912 uses patent-pending circuit techniques
to achieve further reduction of power beyond what is
possible by input current limiting alone.
For low-cost applications, Maxim Integrated offers a pin-
compatible version of this device, the MAX31913, which
does not include the patent-pending current-switching
circuitry included in the MAX31912.
Benets and Features
●Ultra-Low Power and Heat Dissipation
• Low Quiescent Current (1.6mA, typ)
• Highly Accurate and Stable Input Current Limiters,
Adjustable from 0.5mA to 6mA
• Special (Patent-Pending) Ultra-Low-Power Mode
with Switched Current Limiters
• Energy-Less Field-Side LED Drivers
●High Integration Reduces BOM Count, Board Size,
and System Cost
• 8 High-Voltage Input Channels (36V max)
• On-Chip 8-1 Serialization with SPI Interface,
• On-Chip 5V Regulator
• On-Chip Overtemperature Indicator
• Dual On-Chip Field Supply Voltage Monitors
• Integrated Debounce Filters, Selectable from 0 to 3ms
●Robust Features and Performance for Industrial
Environments
• Multibit CRC Code Generation and Transmission for
Error Detection and More Reliable Data Transmission
• High ESD Immunity on All Field Input Pins
●Accepts Industry Standard Input Types
• Congurable for IEC 61131-2 Input Types 1, 2, and 3
●Flexible Power Supply Capability Enables Usage in
5V, 12V, 24V, and Higher Voltage Systems
• Wide Operating Field Supply Range of 7V to 36V
• Can Be Powered from the Logic-Side Using a 5V
Supply
Applications
●Digital Input Modules for PLCs
●Industrial, Building, and Process Automation
●Motor Control
EVALUATION KIT AVAILABLE
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
SOUT
CS
MODESEL
SIN
DB1
DB0
FAULTB
5VOUT
VCC24V
RIREF
GND
RT1
IN1
RT8
IN8
VREF
INPUT CHANNEL 0
VREF
SENSORS
24V
CRC GEN.
µCONTROLLER
OR
ISOLATION
5V
5V REGULATOR
INPUT CHANNEL 7
SUPPLY
MONITOR
TEMP
MONITOR
SWITCHED
CURRENT
LIMITER
LP
FILTER
CLK
VOLTAGE
COMPARATOR
SERIALIZER
MAX31912
Block Diagram
TSSOP
Junction-to-Ambient Thermal Resistance (θJA)...........37°C/W
Junction-to-Case Thermal Resistance (θJC)..................2°C/W
(Note 1)
(Voltages relative to GND.)
Voltage Range on VCC24V ....................................-0.3V to +45V
Voltage Range on IN1–IN8 ...................................-0.3V to +45V
Voltage Range on IN1–IN8
(through 2.2kΩ resistors) ....................................-45V to +45V
Voltage Range on DB0/DB1, CLK, SIN,
CS, MODESEL ............................... -0.3V to (V5VOUT + 0.3V)
Continuous Power Dissipation (TA = +70°C)
TSSOP (derate 27mW/°C above +70°C) ...............2162.2mW
Operating Temperature Range
Ambient Temperature ..................................... -40°C to +125°C
Junction Temperature ..................................... -40°C to +150°C
Storage Temperature Range ............................ -55°C to +125°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) ....................................... +260°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Field Supply Voltage VCC24V (Note 3) 7 36 V
Field Inputs Voltage VINn (Note 4) -0.3 36 V
Logic Inputs Voltage VLOGIC 0 5.5 V
Current-Limit Setting Resistor RREF 15 kΩ
Field Input Data Rate fIN (Note 5) 200 kHz
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
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Note 1: 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.
Absolute Maximum Ratings
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 Thermal Characteristics
Recommended Operating Conditions (Note 2)
(VCC24V = 7V to 36V, TJ = -40°C to +150°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Field-Supply Current ICC24V IN1–IN8 = 24V, 5VOUT = open,
RT1–RT8 = GND, all logic inputs open 1.6 2.3 mA
Field-Supply UV1 Alarm Off/On VONUV1 9 10 V
Field-Supply UV1 Alarm On/Off VOFFUV1 7 8 V
Field-Supply UV2 Alarm Off/On VONUV2 16.5 18 V
Field-Supply UV2 Alarm On/Off VOFFUV2 14 15.5 V
LED On-State Current IRT-ON RREF = 15kΩ, VCC24V = 18V to 30V 2.2 mA
Field Input Threshold High-to-
Low VIN-(INF) 2.2kΩ external series resistor 78.4 V
Field Input Threshold Low-to-
High VIN+(INF) 2.2kΩ external series resistor
(Note 12) 9.4 10.2 V
Field Input Hysteresis VHYS(INF) 2.2kΩ external series resistor
(Note 12) 1 V
Input Threshold High-to-Low
(at IC pin) VTH-(INP) 33.4 V
Input Threshold Low-to-High
(at IC pin) VTH+(INP) (Note 12) 4.4 5 V
Input Threshold Hysteresis
(at IC pin) VHYS(INP) (Note 12) 1 V
Field Input Pin Resistance RINP 0.8 kΩ
Field Input Current Limit IINLIM
RREF = 15kΩ, VCC24V = 18V to 30V,
TA = +25°C to +125°C (Note 6) 2.2 2.4 2.7 mA
Filter Time Constant tFILTER
DB1/DB0 = 0/0: no ltering 0
ms
DB1/DB0 = 0/1 0.008 0.025 0.038
DB1/DB0 = 1/0 0.25 0.75 1.1
DB1/DB0 = 1/1 1.0 3 4.5
Linear Regulator Output V5VOUT Max ILOAD = 50mA 4.75 5.0 5.25 V
Regulator Line Regulation dVREGLINE ILOAD = 50mA 10 mV
Regulator Load Regulation dVREGLOAD ILOAD = 1mA to 50mA 20 mV
Logic-Low Output Voltage VOL IOL = 4mA 0.4 1.0 V
Logic-High Output Voltage VOH IOH = -4mA 4.0 V
Logic-Input Trip Point VIH-IL
0.3 x
V5VOUT
0.5 x
V5VOUT
0.7 x
V5VOUT
V
Logic-Input Leakage Current IIL -50 -30 -15 µA
Overtemperature Alarm TALRM 135 °C
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
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DC Electrical Characteristics
(VCC24V = 7V to 36V, TJ = -40°C to +150°C, unless otherwise noted.) (Note 2)
(VCC24V = 7V to 36V, TJ = -40°C to +150°C, unless otherwise noted.) (Note 2)
Note 2: Limits are 100% production tested at TA = +25°C and TA = +125°C. Limits over the operating temperature range and rel-
evant supply voltage range are guaranteed by design and characterization. Typical values are not guaranteed.
Note 3: If a 24V supply is not available, the device can be powered through V5VOUT. In this mode of operation, the VCC24V sup-
ply must be left unconnected. All other specifications remain identical. The field-supply UV1 and UV2 alarms will be acti-
vated (set to 1), indicating the absence of the 24V supply in this mode of operation.
Note 4: When using suggested external 2.2kΩ series resistors, limits of -3V to +36V apply.
Note 5: fIN refers to the maximum pulse frequency (1/fIN = shortest pulse width) that can be detected from the field sensors and
switches.
Note 6: External resistor RREF can be adjusted to set any desired current limit between 0.5mA and 6mA.
Note 7: See Figure 9.
Note 8: See Figure 6.
Note 9: See Figure 8.
Note 10: See Figure 7.
Note 11: This is the maximum bit transfer rate through the serializer interface.
Note 12: When input current switching is enabled (DB0/DB1 /= 00), there is no Input Threshold Hysteresis. In this case, the Input
Threshold for both falling and rising signal is the High-to-Low Threshold.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Field Input Pulse Width tPW
No external capacitors on pins
IN1-IN8 1 µs
ESD HBM, all pins ±2kV
HBM, IN1-IN8 with respect to GND ±15
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CLK Pulse Duration tCLKPW (Note 7) 20 ns
CS Pulse Duration tCSPW (Note 8) 20 ns
SIN to CLK Setup Time tSU1 (Note 9) 5 ns
SIN to CLK Hold Time tH1 (Note 9) 8 ns
CS to CLK Setup Time tSU2 (Note 10) 8 ns
CS to CLK Recovery Time tREC (Note 10) 12 ns
Clock Pulse Frequency fCLK (Notes 7, 11) 25 MHz
Propagation Delay, CLK to SOUT tP1 (Note 7) 20 ns
Propagation Delay, CS to SOUT tP2 (Note 8) 20 ns
Rise/Fall Time SOUT/FAULT tR/F (Note 7) 40 ns
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
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AC Electrical Characteristics
AC Electrical Characteristics: SPI Interface
(TA = +25°C, RREF = 15kΩ, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX31912 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
60 11010
1.7
1.6
1.8
1.9
2.2
2.1
2.0
2.3
1.5
-40
CURRENT LIMIT vs. RREF
MAX31912 toc03
RREF (kΩ)
CURRENT LIMIT (mA)
40 50
302010
5.5
0.5
1.5
2.5
3.5
4.5
0
INPUT CURRENT LIMIT
vs. TEMPERATURE
MAX31912 toc04
TEMPERATURE (°C)
CURRENT LIMIT (mA)
1106010
VINn = 24V
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
2.0
-40
INPUT CURRENT LIMIT
vs. FIELD-INPUT VOLTAGE
MAX31912 toc05
FIELD-INPUT VOLTAGE (V)
CURRENT LIMIT (mA)
352515
0.5
1.0
1.5
2.0
2.5
3.0
0
5
VCC24V = 24V
INPUT-VOLTAGE HYSTERESIS
vs. TEMPERATURE
MAX31912 toc06
TEMPERATURE (°C)
INPUT-VOLTAGE HYSTERESIS (V)
1106010
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
2.6
-40
ON-OFF THRESHOLD
OFF-ON THRESHOLD
RIN = 0Ω
INPUT-VOLTAGE HYSTERESIS
vs. TEMPERATURE
MAX31912 toc07
TEMPERATURE (°C)
INPUT-VOLTAGE HYSTERESIS
1106010
7.8
8.2
8.0
8.4
8.6
9.0
8.8
9.2
9.4
9.6
9.8
10.0
7.6
-40
RIN = 2.2Ω
OFF-ON THRESHOLD
ON-OFF THRESHOLD
SUPPLY CURRENT
vs. VCC24V FIELD SUPPLY
MAX31912 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
1.65
1.60
1.70
1.75
1.80
1.85
1.90
1.55
5 15 25 35
LDO LOAD REGULATION
MAX31912 toc08
5VOUT OTPUT CURRENT (mA)
5VOUT VOLTAGE (V)
4.92
4.94
4.96
4.98
5.00
5.02
5.04
5.06
5.08
5.10
4.90
0 40 50302010
LDO LINE REGULATION
MAX31912 toc09
SUPPLY VOLTAGE (V)
5VOUT VOLTAGE (V)
4.92
4.94
4.96
4.98
5.00
5.02
5.04
5.06
5.08
5.10
4.90
6363126211611
I5VOUT = 5mA
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
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Typical Operating Characteristics
(TA = +25°C, RREF = 15kΩ, unless otherwise noted.)
LDO LINE REGULATION
MAX31912 toc10
SUPPLY VOLTAGE (V)
5VOUT VOLTAGE (V)
4.92
4.94
4.96
4.98
5.00
5.02
5.04
5.06
5.08
5.10
4.90
6 363126211611
I5VOUT = 50mA
LDO OUTPUT
vs. VCC24V FIELD SUPPLY
MAX31912 toc11
SUPPLY VOLTAGE (V)
5VOUT OTPUT VOLTAGE (V)
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
4.5
4342414
I5VOUT = 50mA
LDO OUTPUT VOLTAGE
vs. TEMPERATURE
MAX31912 toc12
AMBIENT TEMPERATURE (°C)
5VOUT VOLTAGE (V)
4.92
4.94
4.96
4.98
5.00
5.02
5.04
5.06
5.08
5.10
4.90
-40 1106010
I5VOUT = 0mA
LDO OUTPUT VOLTAGE
vs. TEMPERATURE
MAX31912 toc13
AMBIENT TEMPERATURE (°C)
5VOUT VOLTAGE (V)
4.92
4.94
4.96
4.98
5.00
5.02
5.04
5.06
5.08
5.10
4.90
-40 1106010
I5VOUT = 5mA
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
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Typical Operating Characteristics (continued)
PIN NAME FUNCTION
1, 2 DB0, DB1 Debounce (Filtering) Time Select Inputs. These inputs also determine the current
switching frequency. See also Table 1 for details.
3, 5, 7, 9, 11, 18,
20, 22 IN1–IN8 Field Inputs
4, 6, 8, 10, 12,
17, 19, 21 RT1–RT8 Energyless LED Driver Outputs. Connect to GND if LEDs are not required.
13 RIREF Current-Limiter Reference Resistor
14 VCC24V Field-Supply Voltage
15 5VOUT 5V Regulator Output
16 FAULT Active-Low Undervoltage Alarm
23 SOUT Serial-Data Out
24 CS Active-Low Chip-Select Input
25 CLK Serial-Clock Input
26 MODESEL
Mode-Select Input
MODESEL = 1: Selects 8-bit shift register
MODESEL = 0: Selects 16-bit shift register
27 SIN Serial-Data Input
28 GND Field Ground
— EP Exposed Pad. Must be connected to the PCB ground plane.
TOP VIEW
MAX31912
254 CLKRT1
263 MODESELIN1
272 SIN
DB1
281 +GNDDB0
227 IN8
IN3
236 SOUTRT2
218 RT8RT3
209 IN7IN4
1910 RT7RT4
1811 IN6IN5
1712 RT6RT5
1613 FAULT
RIREF
245 CS
IN2
1514 5VOUTVCC24V
EP
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Pin Description
Pin Conguration
Detailed Description
Input Current Clamp
The MAX31912 industrial interface serializer inputs (IN1–
IN8) sense the state (on vs. off) of field sensors by moni-
toring both voltage and current flowing through the sensor
output. The current sinking through these input pins rises
linearly with input voltage until the limit set by the current
clamp is reached. Any voltage increase beyond this point
does not increase the input current any further.
The value of the current clamp is adjustable through an
external resistor connected between the RIREF pin and
GND. Pins RT1–RT8 are connected through LEDs that
recycle the current from the eight inputs to provide visual
status indication without consuming additional current. If
LEDs are not used, these pins must be connected directly
to GND to provide a return path for the input current.
The voltage and current at the IN1–IN8 input pins are
compared against internally set references to determine
whether the sensor is on (logic 1) or off (logic 0). The trip
points determining the on/off status of the sensor satisfy
the requirements of IEC 61131-2 Type 1 and 3 switches.
The device can also be configured to work as a Type 2
switch.
Glitch Filter
A digital glitch filter provides debouncing and filtering of
noisy sensor signals. The time constant of this filter is pro-
grammable from 0ms to 3ms through the DB0 and DB1
pins. See Table 1 for debounce settings.
To provide the digital glitch filter, the device checks that an
input is stable for at least three clock cycles. The duration
of a clock cycle is 1/3 of the selected debounce time. If the
input is not stable for at least three clock cycles, the input
change is not sent to the internal shift register. See
Table 1
for current switching settings.
Low-Power Current Clamp Switching
The MAX31912 uses a patent-pending switched cur-
rent limiter to reduce power consumption below what is
achievable by current limiting alone. The internal filter
clock is used to switch input current between 100% and
20% of the chosen current limit. For example, if the cur-
rent limit is set to 2.4mA, the input current will switch
between 2.4mA and 0.48mA. The filter clock switches
input current at a 50% duty cycle. The clock period for
current switching is automatically selected by the DB1
and DB0 glitch filter settings. See Table 1 for current
switching settings.
GND
MODESEL
DB1
DB0
5VOUT
LED 1–8
SIN
CLK
CS
SOUT
FAU LT
CLK
CS
SOUT
FAU LT
ISOLATION
JUMPERS TO
5VOUT
AND GND
C4
VDD_LOGIC
RREF
RINX
R1
24V
fIN1–8
RIREF
C1
IN1–8
RT1–8
Note: See Figure 1 for additional components needed for EMC.
VCC24V
MAX31912
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Basic Application Circuit
Table 1. Debounce/Current Switching Period Settings
Figure 1. Operation of Patent-Pending Switched Current Limiter
DB1 DB0 BINARY VALUE DEBOUNCE TIME CURRENT SWITCHING PERIOD
0 0 0 0 DC (disabled)
0 1 1 25µs 8µs
1 0 20.75ms 0.25ms
1 1 3 3ms 1ms
24V
0V tDELAY tDELAY
100% ILIMIT
20% ILIMIT
TIME
INTERNAL FILTER CLOCK
COMPARATOR OUTPUT IS LATCHED INTO FILTER ON
RISING EDGE OF CLOCK
INPUT CURRENT LIMIT
SENSOR OUTPUT VOLTAGE
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Reading Serial Data
The filtered outputs of the input comparators are latched
into a shift register at the falling edge of CS. Clocking the
CLK pin, while CS is held low, shifts the latched data out
of SOUT 1 bit at a time.
The internal data serializer comprises a 16-bit shift reg-
ister, containing 8 bits of data corresponding to the eight
field inputs, as well as an 8-bit status byte containing sup-
plementary status and CRC information. The status byte
contains 1 bit representing the status of the field-supply
voltage (UV1), 1 bit representing the status of the internal
temperature monitor (OT), a 5-bit CRC code internally
calculated and generated, 1 bit representing a secondary
voltage supply monitor (UV2).
The undervoltage (UV1) bit is normally 1. If the supply
voltage falls below VOFFUVLO, the UV1 becomes a 0.
The UV1 bit returns to 1 once the supply voltage has
returned above VONUVLO.
The overtemperature (OT) bit is normally 0. If the junc-
tion temperature increases to above TALRM, the OT bit
becomes a 1. The bit returns to 0 once the junction tem-
perature has returned below TALRM.
The CRC code can be used to check data integrity during
transfer from the device to an external microcontroller. In
applications where the integrity of data transferred is not
of concern, the CRC bits can be ignored. The CRC uses
the following polynomial:
P(x) = x5 + x4 + x2 + x0
The number of bits in the internal serializer can be
selected between 8 bits or 16 bits. The MODESEL
pin is used to configure the serializer as an 8-bit
(disabling the status byte) or 16-bit shift register. In 8-bit
mode, only the eight field input states are transferred
through the SPI port and the status byte is ignored.
Therefore, in multiple IC applications (input channels
greater than 8), if desired, only a single status byte can
be generated and transmitted for any number of input
channels.
The shift register contents are read only (no write
capability exists) through the SPI-compatible
interface.
For higher input counts than 8, multiple devices can
be cascaded. In this case, the SOUT pin of one
device should be connected to the SIN pin of the next
device, effectively cascading the internal shift regis-
ters. The CLK and CS pins of all the devices should be
connected together in this configuration. See the
Serial-Port Operation section for more detailed
information on operating the SPI interface.
Temperature Monitoring
The internal junction temperature of the device is
constantly monitored. An alarm is raised, by asserting the
OT bit to a 1.
Supply Voltage Monitoring
A primary supply voltage monitor circuit constantly
monitors the field-supply voltage. If this voltage falls
below a threshold (VOFFUV1), an alarm is raised by
asserting the FAULT pin, indicating that the part is expe-
riencing a fault condition and the data in the serializer is
not to be trusted. In addition, the device resets the UV1
bit to a 0. Once the field-supply voltage has recovered
and goes above VONUV1, the FAULT pin is released. A
secondary supply voltage monitor circuit also monitors
the field-supply voltage. This secondary monitor only
raises a flag in the serializer, by resetting the UV2 bit to
0 (it does not assert the FAULT pin), if the field supply
drops below VOFFUV2. Once the supply voltage goes
back above VONUV2, the UV2 bit is set to 1. The second-
ary supply monitor has higher trip points and its purpose
is to warn the system that the supply voltage is below
specifications (approximately 24V - 20%). Whereas the
purpose of the primary supply monitor is to warn that
the supply voltage has dropped to a value close to the
minimum operating voltage of the IC.
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Applications Information
EMC Standards Compliance
The external components shown in Figure 1 allow the
device to operate in harsh industrial environments.
Components were chosen to assist in suppression of
voltage burst and surge transients, allowing the system
to meet or exceed international EMC requirements.
Table 2 lists an example device for each component
in Figure 2. The system shown in Figure 2, using the
components shown in Table 2, is designed to be robust
against IEC fast transient burst, surge, conducted RFI
specifications and ESD specifications (IEC 61000-4-4,
-5, -6, and -2).
Figure 2. Typical EMC Protection Circuitry
Note: For higher EFT performance, a minimum 1nF, 1000V capacitor can be added from nodes fIN1-8 to Earth or Ground. For
additional methods to improve EFT robustness, please check the Maxim website regularly for upcoming application notes currently
being developed.
Table 2. Recommended Components
COMPONENT DESCRIPTION REQUIRED/RECOMMENDED/OPTIONAL
C0 4.7nF, 2kV polypropylene capacitor Recommended
C1 10µF, 60V ceramic capacitor Required
C3 100nF, 10V ceramic capacitor Recommended
C4 4.7µF, 10V low ESR ceramic capacitor Required
C5 100nF, 100V ceramic capacitor Recommended
D0 36V fast zener diode (ZSMB36) Recommended
D1 General-purpose rectier (IN4007) Optional: For reverse-polarity protection.
LED1 –LED8 LEDs for visual input status indication Optional
R1 150Ω, 1/3W MELF resistor Required
RINX 2.2kΩ, 1/4W MELF resistor Required
RREF 15kΩ, 1/8W resistor Required
GND
MODESEL
DB1
DB0
5VOUT
SIN
CLK
CS
SOUT
FAULT
CLK
CS
SOUT
FAULT
ISOLATION
JUMPERS TO 5VOUT
AND GND
C4C3
VDD_LOGIC
RREF
0V
RINX
fIN1–8
RIREF
IN1–8
RT1–8
*IF LEDS ARE NOT USED, USER MUST GROUND THE RT PINS.
D1
VCC24V
MAX31912
R1
24V
EARTH
EARTH
GROUND
D0 C1
C0
C0 C5
LED 1–8*
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Serial-Port Operation
Serial output of the device functions in one of two
modes, depending on the MODESEL setting (Table 3).
With MODESEL = 0, the device output includes a 5-bit
CRC, an undervoltage alarm, and an overtemperature
alarm. See the Detailed Description for CRC, undervolt-
age, and overtemperature functional descriptions. With
MODESEL = 1, the device outputs only the state of the
IN1–IN8 inputs and omits the CRC, undervoltage alarm,
and overtemperature alarm.
Daisy-Chain Operation
For systems with more than eight sensor inputs, multiple
devices can be daisy-chained to allow access to all data
inputs through a single serial port. When using a daisy-
chain configuration, connect SOUT of one of the devices
to the SIN input of another upstream device. CS and SCK
of all devices in the chain should be connected together
in parallel (see Figure 3). In a daisy-chain configuration,
external components used to enhance EMC robustness
do not need to be duplicated for each device of a circuit
board. Figure 5 illustrates a 16-input application.
SPI Waveforms
The serial output of the device adheres to the SPI proto-
col, running with CPHA = 0 and CPOL = 0. Input states
on IN1–IN8 are latched in on the falling edge of CS. The
transfer of data out of the slave output, SOUT, starts
immediately when CS is asserted (i.e., MSB is output
onto SOUT independent of CLK). The remaining data bits
are shifted out on the falling edge of CLK. The data bits
are written to the output SOUT with MSB first. When CS
is high, SOUT is high impedance. The resultant timing is
shown in Figure 6. Note that all bits after IN1 are invalid
if 8-bit operation mode is selected with the MODESEL
input. Figure 7, Figure 8, Figure 9, and Figure 10 illustrate
SPI timing specifications.
Figure 3. Daisy-Chain Operation
Table 3. MODESEL Settings
MODESEL SETTING FUNCTIONALITY
016-bit output; [IN8–IN1][CRC (5 bit)][UV1][OT][UV2]
1 8-bit output; [IN8–IN1]
MAX31912 MAX31912 MAX31912
SIN
SOUT
SIN
SOUT
SIN
SOUT
TO µCONTROLLER
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Powering the Device Through the 5VOUT Pin
The device can alternatively be powered using a 5V
supply connected to the 5VOUT pin. In this case a 24V
supply is no longer needed and the VCC24V supply must
be kept unconnected. (see Figure 4)
In this configuration, the device will always indicate
a UVFAULT (UV1 and UV2) and the FAULT pin will
always be active (pulled low). Faults due to the Supply
Voltage monitoring will not be available. Faults due to the
Temperature monitor can only be read through the SPI
interface.
This configuration has lower power consumption and
heat dissipation since the on-chip 5V voltage regulator is
disabled.
Figure 4. Basic Application Powered Through 5VOUT
MAX31912
5VOUT
VCC24V
IN1-8
RT1-8
RIREF GND
DB0
DB1
MODESEL
SIN
CLK
CS
SOUT
FIN1-8
JUMPERS TO
5V AND GND
R
INX
R
REF
C3
5V
C1
NOT
CONNECTED
FAULT
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Figure 5. 16-Input Application Circuit
MODESEL
DB1
DB0
5VOUT
CLK
CS
SOUT
FAULT
CLK
CS
SOUT
FAULT
ISOLATION
SIN
JUMPERS TO
5VOUT
AND GND
JUMPERS TO
5VOUT
AND GND
C4C3
C4C3
VDD_LOGIC
RREF
0V
D1
RINX
fIN1–8
RIREF GND
IN1–8
RT1–8
VCC24V
MAX31912
R1
24V
D0 C1
C0
C0
GND
FAULT
SOUT
CS
CLK
SIN
MODESEL
DB1
DB0
5VOUT
RREF
RINX
fIN1–8
RIREF
C1
IN1–8
RT1–8
VCC24V
MAX31912
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Figure 6. SPI Communication Example
Figure 7. SPI Timing Diagram 1
Figure 8. SPI Timing Diagram 2
Figure 9. SPI Timing Diagram 3
Figure 10. SPI Timing Diagram 4
CLK
SOUT
IN8 –IN1
IN8 IN7 IN6 IN5 IN4 IN3 IN2 IN1 CRC4 CRC3 CRC2 CRC1 CRC0 UV1 OT UV2
VALID
CS
SOUT
tCSPW tP2
CS
CLK
tSU2 tREC
CS
CLK
SIN
tSU1 tH1
SIN VALID
tCLKPW
1/fCLK
tR/F
tR/F
tP1
SOUT
CLK
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+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
PART TEMP RANGE PIN-
PACKAGE CARRIER
MAX31912AUI+ -40°C to +125°C 28 TSSOP Bulk
MAX31912AUI+T -40°C to +125°C 28 TSSOP Tape
and Reel PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
28 TSSOP-EP U28E+4 21-0108 90-0146
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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.
Chip Information
PROCESS: S45JRS
Ordering Information
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
03/14 Initial release —
17/14 Updated Input Current Clamp section 8
2 2/15 Updated page 1 content 1
34/15 Updated Reading Serial Data section, IEC diagram, and added Powering the
Device Through the 5VOUT Pin section 11-13, 15
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 specications 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.
MAX31912 Ultra-Low Power Industrial, Octal,
Digital Input Translator/Serializer
© 2015 Maxim Integrated Products, Inc.
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Revision History
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.
