MCP9700 datasheet(9/18 Pages) MICROCHIP

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DS21942B-page 9

MCP9700/01

4.4

Thermal Considerations

The MCP9700/01 measures temperature by monitor-

ing the voltage of a diode located in the die. A

low-impedance thermal path between the die and the

PCB

provided

the

pins.

Therefore,

the

MCP9700/01 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. This limi-

tation 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 MCP9700/01 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 5-1.

EQUATION 4-2:

EFFECT OF

SELF-HEATING

At TA = +25°C (VOUT = 0.75V) and maximum specifica-

tion of IDD =12µA, VDD = 5.5V and IOUT = +100 µA,

the self-heating due to power dissipation (TJ – TA) is

0.179°C.

–

JA VDDIDD

OUT

–

()

OUT

()

Where:

TJ = Junction Temperature

TA = Ambient Temperature

JA = Package Thermal Resistance

(331°C/W)

VOUT = Sensor Output Voltage

IOUT = Sensor Output Current

IDD = Operating Current

VDD = Operating Voltage

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