MCP9700-ESLASHTO datasheet(9/22 Pages) MICROCHIP

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DS20001942G-page 9

MCP9700/9700A and MCP9701/9701A

4.2

Shutdown Using Microcontroller

I/O Pin

The 6 µA (typical) low operating current of the

MCP9700/9700A and MCP9701/9701A family makes it

ideal for battery-powered applications. However, for

applications that require a tighter current budget, this

device can be powered using a microcontroller

Input/Output (I/O) pin. The I/O pin can be toggled to

shut down the device. In such applications, the micro-

controller internal digital switching noise is emitted to

the MCP9700/9700A and MCP9701/9701A as power

supply noise. However, this switching noise compro-

mises measurement accuracy, therefore a decoupling

capacitor and series resistor will be necessary to filter

out the system noise.

4.3

Layout Considerations

The MCP9700/9700A and MCP9701/9701A family of

sensors does not require any additional components to

operate. However, it is recommended that a decoupling

capacitor of 0.1 µF to 1 µF be used between the

VDD and GND pins. In high-noise applications, connect

the power supply voltage to the VDD pin using a

200

 resistor with a 1 µF decoupling capacitor. A high

frequency ceramic capacitor is recommended. It is nec-

essary that the capacitor is located as close as possible

to the VDD and GND pins in order to provide effective

noise protection. In addition, avoid tracing digital lines

in close proximity to the sensor.

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. This limitation applies to plastic-packaged

silicon temperature sensors. If the application requires

the measurement of ambient air, the TO-92 package

should be considered.

The MCP9700/9700A and MCP9701/9701A sensors

are 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 by Equation 4-2.

EQUATION 4-2:

EFFECT OF

SELF-HEATING

TA =+25°C

(VOUT = 0.75V)

and

maximum

specification

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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