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MCP9701-H

Low-Power Linear Active Thermistor ICs

Microchip Technology 

MCP9700/9700A and MCP9701/9701A

4.2 Shutdown Using Microcontroller

I/O Pin

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

low operating current of 6 µA (typical) makes it ideal for

battery-powered applications. However, for

applications that require 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

microcontroller internal digital switching noise is

emitted to the MCP9700/9700A and MCP9701/9701A

as power supply noise. 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

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 200Ω

resistor with a 1 µF decoupling capacitor. A high

frequency ceramic capacitor is recommended. It is

necessary for the capacitor to be 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

measuring ambient air, consider using the TO-92

package.

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

TJ – TA = θJA(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

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

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

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

dissipation (TJ – TA) is 0.179°C.

DS21942E-page 12

© 2009 Microchip Technology Inc.

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