Datasheet

MAX31913
Industrial, Octal, Digital Input
Translator/Serializer
8Maxim Integrated
Basic Application Circuit
Detailed Description
Input Current Clamp
The MAX31913 industrial interface serializer inputs
(IN1–IN8) sense the state (on vs. off) of field sen-
sors by monitoring 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 volt-
age 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 which 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 internal-
ly 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 programmable 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.
GND
MODESEL
DB1
DB0
5VOUT
LED 1–8
SIN
CLK
CS
SOUT
FAULT
CLK
CS
SOUT
FAULT
ISOLATION
NOTE: SEE FIGURE 1 FOR ADDITIONAL COMPONENTS NEEDED FOR EMC.
JUMPERS TO
5VOUT
AND GND
C3
VDD_LOGIC
R
REF
R
INX
R1
24V
f
IN1–8
RIREF
C1
IN1–8
RT1–8
V
CC24V
MAX31913