Datasheet

© 2011 Microchip Technology Inc. DS25095A-page 35
MCP9808
6.0 APPLICATIONS INFORMATION
6.1 Layout Considerations
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 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
power 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. For good temperature sensitivity, add a ground
layer under the device pins, as shown in Figure 6-1.
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-
ature accuracy error of approximately +0.5°C could
result from self-heating if the communication pins
sink/source the maximum current specified.
For example, if the event output is loaded to maximum
I
OL
, Equation 6-1 can be used to determine the effect
of self-heating.
EQUATION 6-1: EFFECT OF
SELF-HEATING
At room temperature (T
A
=+25°C) with maximum
I
DD
= 500 µA and V
DD
= 3.6V, the self-heating due to
power dissipation T
Δ
is +0.2°C for the DFN-8 package
and +0.5°C for the TSSOP-8 package.
FIGURE 6-1: DFN Package Layout (Top View).
T
Δ
θ
JA
V
DD
I
DD
V
OL_Alert
I
OL_Alert
V
OL_SDA
I
OL_SDA
• + • + • ()=
Where:
T
Δ
=T
J
– T
A
T
J
= Junction Temperature
T
A
= Ambient Temperature
θ
JA
= Package Thermal Resistance
V
OL_Alert, SDA
= Alert and SDA Output V
OL
(0.4 V
max
)
I
OL_Alert, SDA
= Alert and SDA Output I
OL
(3 mA
max
)
SDA
SCL
Alert
GND
V
DD
A0
A1
A2
EP9