Datasheet

 2015-2017 Microchip Technology Inc. DS20005426C-page 37
MCP9600
6.0 APPLICATION INFORMATION
6.1 Layout Considerations
The MCP9600 does not require any additional
components to digitize thermocouples. However, it is
recommended that a decoupling capacitor of 0.1 µF to
1 µF be used between the V
DD
and GND pins. A
high-frequency ceramic capacitor is recommended. It
is necessary for the capacitor to be located as close as
possible to the V
DD
and ground pins of the device in
order to provide effective noise protection.
In addition, good PCB layout is key for better thermal
conduction from the PCB temperature to the sensor
die. The PCB provides thermal conduction from the die
to the thermocouple cold-junction; therefore, the com-
ponent placement positioning and the copper layout
techniques are key for optimum cold-junction compen-
sation. The recommended implementation for optimum
temperature sensitivity is to extend a copper ground
pad around the device pins, as shown in Figure 6-1.
FIGURE 6-1: Recommended PCB Layout.
6.1.1 COLD-JUNCTION COMPENSATION
Copper provides better thermal conductivity than PCB
FR4 to the ambient temperature. It also provides better
thermal conduction than the 5 mm x 5 mm MQFN plastic
package, which houses the temperature sensor die.
Therefore, when connecting the thermocouple wire to
the PCB, it is recommended to place the ground copper
between the thermocouple connector footprint, where
dissimilar conductive material is attached to the PCB
and the MCP9600 exposed pad. This allows tempera-
ture to stabilize to the local ambient temperature
(between the thermocouple connector junction and the
PCB copper) and the copper trace conducts the
temperature to the package exposed pad where the
temperature sensor die is placed. The placement of the
sensor exposed pad to the thermocouple connector
junction greatly determines the temperature sensor’s
sensitivity to the local junction temperature changes.
Figure 6-2 demonstrates the recommended techniques.
FIGURE 6-2: Recommended Component
Placement.
6.2 Thermal Considerations
The potential for self-heating errors exist if the
MCP9600 SDA, SCL and alert outputs are heavily
loaded (high current) with pull-up resistors and circuits,
such as high-current LEDs or buzzer loads. The
temperature rise due to self-heat increases the ambient
temperature sensor output, resulting in an increased
temperature offset error compared to the thermocouple
cold-junction ambient temperature.
6.2.1 SELF-HEAT DURING OPERATION
During normal operation, the typical self-heating error
is negligible due to the relatively small current
consumption of the MCP9600. However, this device
integrates a processor to compute the equations
necessary to convert the thermocouple EMF voltage to
degrees Celsius. The processor also maintains the I
2
C
bus. During I
2
C communication, the device operating
current increases to I
DD
= 1.5 mA (typical), I
2
C Active
specification. If the bus is continually polled for data at
frequent intervals, then the processor power dissipates
heat to the temperature sensor and the effect of
self-heat can be detected. Therefore, the recom-
mended implementation is to maintain polling to no
more than three times per temperature conversion
period of 320 ms or use the Burst mode feature to
manage self-heat (refer to Section 6.2.3 “Using Burst
Mode to Manage Self-Heat”). Equation 6-1 can also
be used to determine the effect of self-heat.
Thermal Pad
V
IN+
/V
IN-