MCP9700/9700A and MCP9701/9701A
4.4
Thermal Considerations
The MCP9700/9700A and MCP9701/9701A family
measures temperature by monitoring the voltage of a
diode located in the die. A low-impedance thermal path
between the die and the PCB is provided by the pins.
Therefore, the sensor effectively monitors the
temperature of the PCB. However, the thermal path for
the ambient air is not as efficient because the plastic
device package functions as a thermal insulator from
the die.
However, the plastic device package
insulates the die and restricts device thermal
response
. This limitation applies to plastic-packaged
silicon temperature sensors. If the application requires
measuring ambient air, the PCB needs to be designed
with proper thermal conduction to the sensor pins.
The MCP9700/9700A and MCP9701/9701A is
designed to source/sink 100 µA (max.). The power
dissipation due to the output current is relatively
insignificant. The effect of the output current can be
described using Equation 4-2.
EQUATION 4-2:
EFFECT OF SELF-
HEATING
T
J
–
T
A
=
θ
JA
(
V
DD
I
DD
+
(
V
DD
–
V
OUT
)
I
OUT
)
Where:
T
J
= Junction Temperature
T
A
= Ambient Temperature
θ
JA
= Package Thermal Resistance
(331°C/W)
V
OUT
= Sensor Output Voltage
I
OUT
= Sensor Output Current
I
DD
= Operating Current
V
DD
= Operating Voltage
At T
A
= +25°C (V
OUT
= 0.75V) and maximum
specification of I
DD
= 12 µA, V
DD
= 5.5V and
I
OUT
= +100 µA, the self-heating due to power
dissipation (T
J
– T
A
) is 0.179°C.
©
2006 Microchip Technology Inc.
DS21942C-page 9
MICROCHIP [ MICROCHIP TECHNOLOGY ]
