© 2011 Microchip Technology Inc.

DS22268A-page 9

MCP9501/2/3/4

4.1

Application Information

The

MCP9501/2/3/4

temperature

switch

family

integrates a temperature sensor and a comparator

circuit which outputs an alert signal when the factory

set temperature threshold is exceeded. No additional

component is required for device operation, which

provides simplicity to the system designer. The device

output options provide design flexibility for various

applications such as overtemperature protection circuit

or a closed loop temperature control unit. This device

can be interfaced to a closed loop fan controller

network without the need for a microcontroller.

FIGURE 4-3:

Fan Controller Using

MCP9502.

The MCP9501/2/3/4 provide Open-Drain output where

multiple sensors from multiple PCB hot-spots can be

connected to a single processor I/O input with a wired-

OR configuration. The MCP9501 requires an external

pull-up resistor which can be used to level-shift the alert

signal. For example, if the sensors are powered with

Figure 4-4.

FIGURE 4-4:

MCP9501 Wired-OR Output

Configuration with Level-shift.

4.1.1

LAYOUT CONSIDERATION AND

THERMAL CONSIDERATION

This family of sensors measures temperature by

monitoring the voltage level of a thermal 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 PCB temperature. For

efficient performance, it is recommended to layout the

device as close to the heat source as possible.

When connecting an external resistor to the MCP9501/

3, the current through the pull-up resistor must be

considered to prevent self-heat due to power. This can

be determined using Equation 4-1.

EQUATION 4-1:

EFFECT OF

SELF-HEATING

For example, at room temperature, when the output

specification table), the self heating due to power

Output

HYST

MCP9502

12V

M

OUT

HYST

OUT

HYST

I/O

Micro-

controller

MCP9501

85°C

MCP9503

35°C

Where:

=

Junction Temperature

=

Ambient Temperature

θ

JA

=

Package Thermal Resistance

(220.7 °C/W)

=

Sensor Output Low Voltage

=

Output Current

T

J

T

A

–

θ

I

DD

×

V

OL

I

OUT

×

+

()

=