MCP98242-CE/ST Microchip Technology, MCP98242-CE/ST Datasheet - Page 36

• Manufacturer Part Number: MCP98242-CE/ST
• Description: Board Mount Temperature Sensors JEDEC DIMM SER Outpt Temp Snsr SPD EEPROM
• Manufacturer: Microchip Technology

Specifications of MCP98242-CE/ST

• Full Temp Accuracy: +/- 2 C
• Package / Case: TSSOP-8
• Digital Output - Bus Interface: Serial (2-Wire, I2C)
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Output Type: Digital
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

MCP98242
6.0
6.1
The SDA and SCLK serial interface pins are open-
drain pins that require pull-up resistors. This
configuration is shown in
FIGURE 6-1:
Interface.
The number of devices connected to the bus is limited
only by the maximum rise and fall times of the SDA and
SCLK lines. Unlike I
specify a maximum bus capacitance value. Rather, the
SMBus specification requires that the maximum
current through the pull-up resistor be 350 µA and
minimum 100 µA. Because of this, the value of the pull-
up resistors will vary depending on the system’s bias
voltage (V
system ranges 9 kΩ to 33 kΩ. Minimizing bus capaci-
tance 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, with a maximum
voltage drop of 0.4 V, the MCP98242 is designed to
meet a maximum voltage drop of 0.4 V, with 3 mA of
current. This allows lower pull-up resistor values to be
used, allowing the MCP98242 to handle higher bus
capacitance. In such applications, all devices on the
bus
requirements.
A possible configuration using multiple devices on the
SMBus is shown in
FIGURE 6-2:
SMBus.
DS21996B-page 36
Temperature
must
MCP98242
Master
Sensor
APPLICATIONS INFORMATION
Connecting to the Serial Bus
DD
). The pull-up resistor values for a 3.3 V
meet
Figure
2
R
C specifications, SMBus does not
the
Pull-up Resistors On Serial
Multiple Devices on DIMM
V
SDA SCLK
DD
Figure
R
6-2.
same
R
6-1.
pull-down
MCP98242
SDA
SCLK
Event
EEPROM
24LCS52
Slave
current
6.2
The MCP98242 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 and ground pins of the device in order to provide
effective noise protection.
6.3
A potential for self-heating errors can exist if the
MCP98242 SDA, SCLK and Event lines are heavily
loaded with pull-ups (high current). Typically, the self-
heating error is negligible because of the relatively
small current consumption of the MCP98242. A
temperature accuracy error of approximately 0.5°C
could result from self-heating if the communication pins
sink/source the maximum current specified.
For example, if the Event output is loaded to maximum
I
of self-heating.
EQUATION 6-1:
At room temperature (T
I
power dissipation T
and 0.5°C for the TSSOP-8 package.
T
OL
DD
Where:
Δ
V
I
,
=
OL_Event, SDA
OL_Event, SDA
= 500 µA and V
Equation 6-1
θ
JA
(
V
Layout Considerations
Thermal Considerations
DD
•
θ
I
T
T
T
JA
DD
A
Δ
J
DD
+
= T
= Junction Temperature
= Ambient Temperature
= Package Thermal Resistance
= Event and SDA Output V
= Event and SDA Output I
can be used to determine the effect
V
and GND pins. A high-frequency
OL_Event
Δ
DD
(0.4 V
(3 mA
is 0.2°C for the DFN-8 package
J -
EFFECT OF SELF-
HEATING
= 3.6V, the self-heating due to
© 2008 Microchip Technology Inc.
T
A
A
max
max
•
I
= +25°C) with maximum
OL_Event
)
)
+
V
OL_SDA
OL
•
OL
I
OL_SDA
)