Datasheet

© 2009 Microchip Technology Inc. DS22153C-page 45
MCP9843/98243
6.0 APPLICATIONS INFORMATION
6.1 Layout Considerations
The MCP9843/98243 device does not require any
additional components besides the master controller in
order to measure temperature. However, it is recom-
mended 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
MCP9843/98243 SDA, SCLK 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 MCP9843/
98243. A temperature 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.
T
Δ
θ
JA
V
DD
I
DD
V
OL_Event
I
OL_Event
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_Event, SDA
= Event and SDA Output V
OL
(0.4 V
max
)
I
OL_Event, SDA
= Event and SDA Output I
OL
(3 mA
max
)
A0
A1
A2
GND
V
DD
Event
SCL
SDA
EP9