Datasheet

MAX31865
RTD-to-Digital Converter
11Maxim Integrated
Figure 4. Fault Detection Flowcharts
MASTER-INITIATED FAULT-DETECTION CYCLE - AUTOMATIC MODE
MASTER-INITIATED FAULT-DETECTION CYCLE - MANUAL MODE
N
IS FORCE+,
FORCE2, FORCE-,
RTDIN+, RTDIN-,
PINS > V
DD
OR <
GND
PROTECT PINS AGAINST
±50V
Y
SET BIT D2 OF FAULT
STATUS REGISTER
ADC HALTS UPDATES
SET BIT D0 OF RTD DATA
LSB REGISTER
EVERY CONVERSION FAULT DETECTION
MONITOR PINS
ALWAYS ACTIVE FAULT DETECTION
FAULT DETECTION
MASTER WRITES
100X010Xb TO
CONFIGURATION
REGISTER
NN
IS VREFIN-
>
0.85 x VBIAS
100µs
DELAY
FORCE-INPUT
SWITCH
REMAINS
CLOSED
OPEN
FORCE-
INPUT
SWITCH
FORCE-INPUT
SWITCH
CLOSED
CONFIGURATION
REGISTER SET TO
100X000Xb TO
END FAULT
DETECTION
CYCLE
IS VREFIN-
<
0.85 x VBIAS
IS RTDIN-
<
0.85 x VBIAS
N
SET BIT D5 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
100µs
DELAY
100µs
DELAY
210µs
DELAY
Y
SET BIT D4 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
Y
SET BIT D3 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
Y
Y
100µs
DELAY
OPEN
FORCE-
INPUT
SWITCH
MASTER WRITES
100X100Xb TO
CONFIGURATION
REGISTER
N
IS VREFIN-
>
0.85 x VBIAS
100µs
DELAY
FORCE-INPUT
SWITCH
REMAINS
CLOSED
DID
MASTER WRITE
100X110Xb TO
CONFIGURATION
REGISTER
100µs
DELAY
100µs
DELAY
Y
SET BIT D5 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
N
IS VREFIN-
<
0.85 x VBIAS
SET BIT D4 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
Y
N
FORCE-INPUT
SWITCH
CLOSED
CONFIGURATION
REGISTER SET TO
100X000Xb TO
END FAULT
DETECTION
CYCLE
IS RTDIN-
<
0.85 x VBIAS
N
SET BIT D3 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER
Y
PERFORM
CONVERSION
NN
IS
RTD RESISTANCE
VALUE > HIGH
THRESHOLD
REGISTER
Y
SET BIT D7 OF FAULT
STATUS REGISTER
IS
RTD RESISTANCE
VALUE < LOW
THRESHOLD
REGISTER
CONVERSION
INITIATED
Y
SET BIT D6 OF FAULT
STATUS REGISTER
SET BIT D0 OF RTD DATA
LSB REGISTER