MCP9802 Microchip Technology Inc., MCP9802 Datasheet - Page 22

• Manufacturer Part Number: MCP9802
• Description: 2-wire High-accuracy Temperature Sensor
• Manufacturer: Microchip Technology Inc.

MCP9800/1/2/3
6.0
6.1
The SDA and SCLK serial interface are open-drain pins
that require pull-up resistors. This configuration is
shown in Figure 6-1.
FIGURE 6-1:
Interface.
For the SMBus protocol, the number of devices con-
nected to the bus are limited only by the maximum rise
and fall times of the SDA and SCLK lines. Unlike the
I
bus capacitance value. Rather, it specifies 350 µA
(max.) current through the pull-up resistor. Therefore,
the value of the pull-up resistors will vary depending on
the system’s supply voltage (V
values for a 5V system ranges 14.3 k
Minimizing bus capacitance is still very important, as it
directly affects the rise and fall times of the SDA and
SCLK lines.
Although SMBus specifications only require the SDA
and SCLK lines to pull down 350 µA (max.) with 0.4V
(max.) voltage drop, the MCP9800/1/2/3 is designed to
meet 0.4V (max.) 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
Microchip provides several microcontroller product
lines with Master Synchronous Serial Port Modules
(MSSP) that include I
implements all master and slave functions and simpli-
fies 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 MCP980X
temperature sensor connected to the bus.
DS21909B-page 22
2
C specifications, SMBus does not specify a maximum
APPLICATIONS INFORMATION
Connecting to the Serial Bus
Typical Application
2
Pull-up Resistors On Serial
C interface mode. This module
V
R
DD
R
DD
). The pull-up resistor
MCP980X
SDA
SCLK
to 50 k .
FIGURE 6-2:
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
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
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
The
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 SCLK 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 SCLK pins need to be lightly
loaded.
MCP9800/1/2/3
Microcontroller
Layout Considerations
Thermal Considerations
PIC16F737
TC654
Fan Speed
Controller
DD
and GND pins. A high-frequency
Multiple Devices on SMBus.
SDA SCLK
 2004 Microchip Technology Inc.
measures
Temperature
MCP980X
EEPROM
24LC01
temperature
Sensor
by