MCP970X datasheet(11/26 Pages) MICROCHIP

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DS20001942J-page 11

MCP970X

4.2

Shutdown Using Microcontroller

I/O Pin

The 6 µA (typical) low operating current of the

MCP9700/9700A/9700B and MCP9701/9701A family

makes it ideal for battery-powered applications. How-

ever, for applications that require a tighter current bud-

get, 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/9700B and MCP9701/9701A as

power supply noise. However, this switching noise

compromises measurement accuracy, therefore a

decoupling capacitor and series resistor will be neces-

sary to filter out the system noise.

4.3

Layout Considerations

The MCP9700/9700A/9700B and MCP9701/9701A

family of sensors does not require any additional com-

ponents 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 applica-

tions, 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 necessary 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 dig-

ital lines in close proximity to the sensor.

4.4

Thermal Considerations

The MCP9700/9700A/9700B 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/9700B 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.

TJ TA

–



JA VDDIDD

VDD VOUT

–



IOUT



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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