MCP9808
ature accuracy error of approximately +0.5°C could
result from self-heating if the communication pins
sink/source the maximum current specified.
6.0
6.1
APPLICATIONS INFORMATION
Layout Considerations
For example, if the event output is loaded to maximum
IOL, Equation 6-1 can be used to determine the effect
of self-heating.
The MCP9808 does not require any additional
components besides the master controller in order to
measure temperature. However, it is recommended
that a decoupling capacitor of 0.1 µF to 1 µF be used
between the VDD 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
power and ground pins of the device in order to provide
effective noise protection.
EQUATION 6-1:
EFFECT OF
SELF-HEATING
T
= θ (V
• I
+ V
• I
+ V
• I )
Δ
JA DD DD
OL_SDA OL_SDA
OL_Alert OL_Alert
Where:
TΔ = TJ – TA
In addition, good PCB layout is key for better thermal
conduction from the PCB temperature to the sensor
die. For good temperature sensitivity, add a ground
layer under the device pins, as shown in Figure 6-1.
TJ = Junction Temperature
TA = Ambient Temperature
θJA = Package Thermal Resistance
VOL_Alert, SDA = Alert and SDA Output VOL
(0.4 Vmax
IOL_Alert, SDA = Alert and SDA Output IOL
(3 mAmax
)
6.2
Thermal Considerations
A potential for self-heating errors can exist if the
MCP9808 SDA, SCL and Event lines are heavily
loaded with pull-ups (high current). Typically, the
self-heating error is negligible because of the relatively
small current consumption of the MCP9808. A temper-
)
At room temperature (TA = +25°C) with maximum
IDD = 500 µA and VDD = 3.6V, the self-heating due to
power dissipation TΔ is +0.2°C for the DFN-8 package
and +0.5°C for the TSSOP-8 package.
VDD
A0
SDA
SCL
EP9
Alert
A1
A2
GND
FIGURE 6-1:
DFN Package Layout (Top View).
© 2011 Microchip Technology Inc.
DS25095A-page 35
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