TCN75AVUA. データシートの表示（PDF） - Microchip Technology

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TCN75AVUA.

2-Wire Serial Temperature Sensor

Microchip Technology 

6.0 APPLICATIONS INFORMATION

6.1 Connecting to the Serial Bus

The SDA and SCL serial interface are open-drain pins

that require pull-up resistors. This configuration is

shown in Figure 6-1.

PIC®

MCU

VDD

TCN75A

RR

SDA

SCL

FIGURE 6-1:

Interface.

Pull-up Resistors On Serial

The TCN75A is designed to meet 0.4V (max.) voltage

drop at 3 mA of current. This allows the TCN75A to

drive lower values of pull-up resistors and higher bus

capacitance. In this application, all devices on the bus

must meet the same pull-down current requirements.

6.2 Typical Application

Microchip provides several microcontroller product

lines with Master Synchronous Serial Port Modules

(MSSP) that include the I2C interface mode. This

module implements all master and slave functions and

simplifies the firmware development overhead.

Figure 6-2 shows a typical application using the

PIC16F737 as a master to control other Microchip

slave products, such as EEPROM, fan speed

controllers and the TCN75A temperature sensor

connected to the bus.

PIC16F737

Microcontroller

SDA SCL

TC654

Fan Speed

Controller

24LC01

EEPROM

TCN75A

Temperature

Sensor

FIGURE 6-2:

Bus.

Multiple Devices on I2C™

TCN75A

The ALERT output can be wire-ORed with a number of

other open-drain devices. In such applications, the

output needs to be programmed as an active-low

output. Most systems will require pull-up resistors for

this configuration.

6.3 Layout Considerations

The TCN75A does not require any additional compo-

nents besides the master controller in order to measure

temperature. However, it is recommended that a

decoupling capacitor of 0.1 μF to 1 μF be used

between the VDD and GND pins. A high-frequency

ceramic capacitor is recommended. It is necessary for

the capacitor to be located as close as possible to the

power pins in order to provide effective noise

protection.

6.4 Thermal Considerations

The TCN75A measures temperature by monitoring the

voltage of a diode located in the die. A low-impedance

thermal path between the die and the Printed Circuit

Board (PCB) is provided by the pins. Therefore, the

TCN75A 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.

A potential for self-heating errors can exist if the

TCN75A SDA and SCL communication lines are

heavily loaded with pull-ups. Typically, the self-heating

error is negligible because of the relatively small

current consumption of the TCN75A. However, in order

to maximize the temperature accuracy, the SDA and

SCL pins need to be lightly loaded.

© 2006 Microchip Technology Inc.

DS21935C-page 23

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