MCP9510HT-E datasheet(16/28 Pages) MICROCHIP

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MCP9509/10

DS22114A-page 16

4.6

Application Information

The MCP9509/10 temperature switch integrates a

temperature sensor and a comparator circuit which out-

puts an alert signal when the user programmed tem-

perature threshold is exceeded. The external resistor

value to set the output threshold can be determined

using Table 4-2. A constant current source ISET = 5 µA

(typical) biases the external resistor RSET. A thermal

diode is used to measure ambient temperature. When

the voltage across the thermal diode exceeds the volt-

age across RSET, VSET, the sensor output asserts. The

sensor output de-asserts when the diode voltage drops

below VSET and the user selected hysteresis level.

The MCP9509/10 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 MCP9509 requires an

external pull-up resistor which can be used to level-shift

the alert signal. For example, if the sensors are

powered with 5VDD and the controller or processor is

powered with 3VDD, the external resistor can be

level-shifted by connecting 3VDD to the pull-up resistor

as shown in Figure 4-5. The MCP9510 elliminates the

need for an external resistor while providing wired-Or

function (Figure 4-6). The MCP9510 also provides

push-pull output configuration for a direct connection to

the processor with Active-Low or Active-High assert

polarities.

FIGURE 4-5:

MCP9509 Wired-Or Output

Configuration with Level-shift.

FIGURE 4-6:

MCP9510 Wired-Or Output

Configuration with Internal Pull-up Resistor.

4.6.1

LAYOUT CONSIDERATION AND

THERMAL CONSIDERATION

This family of sensors measure temperature by moni-

toring 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. It is also

recommended to use a de-coupling capacitor of 0.1 µF

to 1 µF between VDD and GND pins for stability.

When connecting an external resistor to the MCP9509

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

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

be determined using Equation 4-3.

EQUATION 4-3:

EFFECT OF

SELF-HEATING

SET

OUT

HYST

5VDD

SET

RSET

OUT

HYST

5VDD

I/O

3VDD

RPULL_UP

Micro-

controller

RSET

MCP9509

3VDD

SET

OUT

HYST

5VDD

SET

RSET

OUT

HYST

5VDD

I/O

Micro-

controller

RSET

MCP9510

OUTSET

5VDD

Where:

Junction Temperature

Ambient Temperature

Package Thermal Resistance

(220.7 °C/W)

VOL

Sensor Output Low Voltage

IOUT

Output Current

–

JA VDD

OUT

()

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