Microchip Technology MCP9800DM-DL2 Data Sheet
2010 Microchip Technology Inc.
DS21909D-page 27
MCP9800/1/2/3
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
that require pull-up resistors. This configuration is
shown in
.
FIGURE 6-1:
Pull-up Resistors on Serial
Interface.
The MCP9800/1/2/3 is designed to meet 0.4V
(maximum) voltage drop at 3 mA of current. This allows
the MCP9800/1/2/3 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.
(maximum) voltage drop at 3 mA of current. This allows
the MCP9800/1/2/3 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 I
lines with Master Synchronous Serial Port modules
(MSSP) that include the I
2
C interface mode. This
module implements all master and slave functions and
simplifies the firmware development overhead.
simplifies the firmware development overhead.
shows a typical application using the
PIC16F737 as a master to control other Microchip
slave products, such as EEPROM, fan speed
controllers and the MCP9800 temperature sensor
connected to the bus.
slave products, such as EEPROM, fan speed
controllers and the MCP9800 temperature sensor
connected to the bus.
FIGURE 6-2:
Multiple Devices on I
2
C™
Bus.
The ALERT output can be wired 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.
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 MCP9800/1/2/3 does not require any additional
components 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 V
components 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 V
DD
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.
For applications where a switching regulator is used to
power the sensor, it is recommended to add a 200Ω
resistor in series to V
the capacitor to be located as close as possible to the
power pins in order to provide effective noise
protection.
For applications where a switching regulator is used to
power the sensor, it is recommended to add a 200Ω
resistor in series to V
DD
to filter out the switcher noise
from the sensor. It is also recommended to add the
series resistor in applications where a linear regulator
is used to step-down a switching regulator voltage to
power the sensor. For example, if a linearly regulated
3.3V from a 5V switching regulator is used to power the
sensor, add a 200Ω series resistor (refer to
series resistor in applications where a linear regulator
is used to step-down a switching regulator voltage to
power the sensor. For example, if a linearly regulated
3.3V from a 5V switching regulator is used to power the
sensor, add a 200Ω series resistor (refer to
FIGURE 6-3:
Power-supply Filter Using a
Single Resistor.
6.4
Thermal Considerations
The MCP9800/1/2/3 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 MCP9800/1/2/3 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
MCP9800/1/2/3 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 MCP9800/1/2/3.
However, in order to maximize the temperature
accuracy, the SDA and SCL pins need to be lightly
loaded.
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 MCP9800/1/2/3 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
MCP9800/1/2/3 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 MCP9800/1/2/3.
However, in order to maximize the temperature
accuracy, the SDA and SCL pins need to be lightly
loaded.
PIC
®
SDA
SCL
SCL
V
DD
R
R
MCU
MCP9800/1/2/3
SDA SCL
PIC16F737
Microcontroller
Temperature
Sensor
24LC01
EEPROM
TC654
Fan Speed
Controller
TCN75A
V
DD
200
MCP9800/1/2/3
Switching
Regulator
Regulator
0.1 µF
bypass
V
DD
200
MCP9800/1/2/3
Switching
Regulator
Regulator
0.1 µF
bypass
Regulator
Linear