Datasheet

MCP9600
DS20005426C-page 40  2015-2017 Microchip Technology Inc.
6.3.3.1 Open-Circuit Detection Technique
For open-circuit detection, the Input Range Flag bit,
bit 4 of the STATUS register (Register 5-6), can be
used to detect open-circuit conditions. This would
require a few external resistors, as shown in
Figure 6-6. The passive circuit does not affect the
MCP9600 accuracy (the recommended value for R
B
is
set to 1 M. When the thermocouple is connected, the
input Common-mode voltage is 0.5 * V
DD
. When the
thermocouple is disconnected, the voltage at the V
IN+
input is 0.66 * V
DD
and the voltage at the V
IN-
input is
pulled down to V
SS
. This change forces the Input
Range Flag bit to be set. The master controller can
momentarily poll the Status bit to detect the open-circuit
condition.
FIGURE 6-6: Adding Open-Circuit
Detection Resistors.
6.3.4 ALIASING AND ANTI-ALIASING
FILTER
Aliasing occurs when the input signal contains time
varying signals with frequency greater than half the
sample rate. In the aliasing conditions, the ADC can
output unexpected codes. The ADC integrates a first
order sync filter; however, an external anti-aliasing filter
can provide an added filter for high noise applications.
This can be done with a simple RC low-pass filter at the
inputs, as shown in Figure 6-7. Open-circuit detection
resistors can also be added, as shown in Figure 6-8.
FIGURE 6-7: Adding a Low-Pass Filter.
FIGURE 6-8: Adding Open-Circuit
Detection Resistors with an Input Low-Pass
Filter.
6.3.5 ESD PROTECTION USING FERRITE
BEADS
Ferrite beads are highly recommended to protect the
MCP9600 and other circuits from ESD discharge
through the thermocouple wire. The beads suppress
fast transient signals, such as ESD, and can be added
in-line to the ADC inputs. In addition, protection diodes
are also recommended, as shown in Figure 6-9.
FIGURE 6-9: Adding Ferrite Beads.
Del Sig
V
IN+
V
IN-
MCP9600
Thermocouple
+
R
B
V
DD
2 R
B
2 R
B
R
B
=1M
Del Sig
V
IN+
V
IN-
Thermocouple
+
C
R
A
R
A
R
A
= 100
C=0.1µF
ADC Core
Del Sig
V
IN+
V
IN-
Thermocouple
+
C
R
A
R
B
V
DD
2 R
B
2R
B
R
A
MCP9600
R
B
=1M
R
A
= 100
C=0.1µF
Del Sig
V
IN+
V
IN-
Thermocouple
+
C
R
A
R
B
V
DD
2R
B
R
A
R
B
= 1M
R
A
= 100
C
= 0.1uF
L = Ferrite Bead
D = Diode
L
L
MCP9600
V
DD
2R
B
D
D
D
D