MAX6642ATT90+T Maxim Integrated Products, MAX6642ATT90+T Datasheet - Page 10

• Manufacturer Part Number: MAX6642ATT90+T
• Description: IC TEMP SENSOR SMBUS 6-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX6642ATT90+T

• Function: Temp Monitoring System (Sensor)
• Topology: ADC, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, 0°C ~ 150°C
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: No
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 6-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: MAX6642ATT90+T; MAX6642ATT90+TTR

±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
III. A thermal diode on the substrate of an IC is normally
a PNP with its collector grounded. Connect the anode
(emitter) to DXP and the cathode to GND of the
MAX6642.
If a sense transistor with an ideality factor other than
1.008 is used, the output data is different from the data
obtained with the optimum ideality factor. Fortunately,
the difference is predictable.
Assume a remote-diode sensor designed for a nominal
ideality factor n
perature of a diode with a different ideality factor n
The measured temperature T
where temperature is measured in Kelvin and
n
As an example, assume you want to use the MAX6642
with a CPU that has an ideality factor of 1.002. If the
diode has no series resistance, the measured data is
related to the real temperature as follows:
For a real temperature of +85°C (358.15K), the mea-
sured temperature is +82.91°C (356.02K), an error of
-2.13°C.
Series resistance in a sense diode contributes addition-
al errors. For nominal diode currents of 10µA and
100µA, the change in the measured voltage due to
series resistance is:
Since +1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
10
NOMIMAL
______________________________________________________________________________________
ΔV
T
ACTUAL
for the MAX6642 is 1.008.
M
= R
T
NOMINAL
M
S
198 6
=
=
(100µA - 10µA) = 90µA
90
T
T
T
M
M
ACTUAL
.
μ
( .
⎛
⎜
⎝
Ω
1 00599
V
μ
°
n
C
V
NOMINAL
is used to measure the tem-
Effect of Series Resistance
=
⎛
⎜
⎝
n
M
0 453
1
n
.
NOMINAL
)
can be corrected using:
n
1
⎞
⎟ =
⎠
°
Ω
C
T
⎞
⎟
⎠
M
⎛
⎜
⎝
1 008
1 002

.
.
R
S
⎞
⎟ =
⎠
1
.
The effects of the ideality factor and series resistance
are additive. If the diode has an ideality factor of 1.002
and series resistance of 3Ω, the total offset can be cal-
culated by adding error due to series resistance with
error due to ideality factor:
for a diode temperature of +85°C.
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
When the remote-sensing diode is a discrete transistor,
connect its collector and base together. Table 7 lists
examples of discrete transistors that are appropriate for
use with the MAX6642.
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage at
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected tempera-
ture, the forward voltage must be less than 0.95V at
100µA. Large power transistors must not be used. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < ß <150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
V
Manufacturers of discrete transistors do not normally
specify or guarantee ideality factor. This is normally not
a problem since good-quality discrete transistors tend
to have ideality factors that fall within a relatively narrow
Table 7. Remote-Sensor Transistor
Manufacturers
Note: Discrete transistors must be diode connected (base short-
ed to collector).
Central Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
Zetex (England)
BE
characteristics.
MANUFACTURER
1.36°C - 2.13°C = -0.77°C
3
Ω ×
0 453
.
Discrete Remote Diodes
°
Ω
C
= +
1 36
.
FMMT3906CT-ND
°
C
MODEL NO.
KST3906-TF
CMPT3906
SMBT3906
SST3906