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.
6.0
6.1
APPLICATIONS INFORMATION
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.
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.
VDD
TCN75A
R
R
SDA
SCL
PIC®
MCU
6.4
Thermal Considerations
FIGURE 6-1:
Interface.
Pull-up Resistors On Serial
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.
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.
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.
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.
SDA
SCL
PIC16F737
Microcontroller
24LC01
EEPROM
TC654
Fan Speed
Controller
TCN75A
Temperature
Sensor
2
FIGURE 6-2:
Bus.
Multiple Devices on I C™
© 2006 Microchip Technology Inc.
DS21935C-page 23
MICROCHIP [ MICROCHIP ]
