MCP9700-ESLASHTO datasheet(9/18 Pages) MICROCHIP

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DS21942C-page 9

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

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

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

specification of IDD =12µA, VDD = 5.5V and

IOUT = +100 µA, the self-heating due to power

dissipation (TJ –TA) is 0.179°C.

TJ TA

–

JA VDDIDD

VDD VOUT

–

()

IOUT

()

Where:

TJ = Junction Temperature

TA = Ambient Temperature

θJA = Package Thermal Resistance

(331°C/W)

VOUT = Sensor Output Voltage

IOUT = Sensor Output Current

IDD = Operating Current

VDD = Operating Voltage

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