MAX31865
RTD-to-Digital Converter
FAULT DETECTION
ALWAYS ACTIVE FAULT DETECTION
MONITOR PINS
EVERY CONVERSION FAULT DETECTION
IS FORCE+,
FORCE2, FORCE-,
RTDIN+, RTDIN-,
IS
IS
RTD RESISTANCE
VALUE > HIGH
THRESHOLD
REGISTER
RTD RESISTANCE
VALUE < LOW
THRESHOLD
REGISTER
N
CONVERSION
INITIATED
PERFORM
CONVERSION
N
N
PINS > V OR <
DD
GND
Y
Y
Y
PROTECT PINS AGAINST
±±5V
SET BIT D7 OF FAULT
STATUS REGISTER
SET BIT D6 OF FAULT
STATUS REGISTER
SET BIT D2 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
ADC HALTS UPDATES
SET BIT D5 OF RTD DATA
LSB REGISTER
MASTER-INITIATED FAULT-DETECTION CYCLE - AUTOMATIC MODE
MASTER WRITES
155X515Xb TO
CONFIGURATION
REGISTER
FORCE-INPUT
SWITCH
REMAINS
CLOSED
OPEN
FORCE-
INPUT
IS VREFIN-
>
5.8± x VBIAS
IS VREFIN-
<
0.85 x VBIAS
155µs
DELAY
N
100µs
DELAY
210µs
DELAY
N
SWITCH
Y
Y
SET BIT D5 OF FAULT
STATUS REGISTER
SET BIT D4 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
CONFIGURATION
REGISTER SET TO
155X555Xb TO
FORCE-INPUT
SWITCH
CLOSED
IS RTDIN-
<
0.85 x VBIAS
END FAULT
DETECTION
CYCLE
N
100µs
DELAY
Y
SET BIT D3 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
MASTER-INITIATED FAULT-DETECTION CYCLE - MANUAL MODE
DID
MASTER WRITES
FORCE-INPUT
SWITCH
REMAINS
CLOSED
OPEN
FORCE-
INPUT
MASTER WRITE
100X110Xb TO
CONFIGURATION
REGISTER
IS VREFIN-
>
0.85 x VBIAS
IS VREFIN-
<
0.85 x VBIAS
100X100Xb TO
CONFIGURATION
REGISTER
100µs
DELAY
N
100µs
DELAY
Y
100µs
DELAY
N
SWITCH
Y
Y
N
SET BIT D5 OF FAULT
STATUS REGISTER
SET BIT D4 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
CONFIGURATION
REGISTER SET TO
100X000Xb TO
FORCE-INPUT
SWITCH
CLOSED
IS RTDIN-
<
0.85 x VBIAS
END FAULT
DETECTION
CYCLE
N
100µs
DELAY
Y
SET BIT D3 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
Figure 4. Fault Detection Flowcharts
Maxim Integrated
11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
