MAX6615AEE+ Maxim Integrated Products, MAX6615AEE+ Datasheet - Page 17

• Manufacturer Part Number: MAX6615AEE+
• Description: IC TEMP MONITOR DL-CH 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6615AEE+

• Function: Fan Control, Temp Monitor
• Topology: ADC, PWM Generator, Tach Counter
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 9. Data Error vs. Temperature Using a Betatherm
10K3A1 Thermistor
NTC thermistors are resistive temperature sensors
whose resistance decreases with increasing tempera-
ture. They are available in a wide variety of packages
that are useful in difficult applications such as measure-
ment of air or liquid temperature. Some can operate
over temperature ranges beyond that of most ICs. The
relationship between temperature and resistance in an
NTC thermistor is very nonlinear and can be described
by the following approximation:
where T is absolute temperature in Kelvin, R is the ther-
mistor’s resistance, and A, B, and C are coefficients that
vary with manufacturer and material characteristics.
The highly nonlinear relationship between temperature
and resistance in an NTC thermistor makes it somewhat
more difficult to use than a digital-output temperature-
sensor IC. However, by connecting the thermistor in
series with a properly chosen resistor and using the
MAX6615/MAX6616 to measure the voltage across the
resistor, a reasonably linear transfer function can be
obtained over a limited temperature range. Accuracy
increases over smaller temperature ranges.
Figures 9 and 10 show a good relationship between
temperature and data. This data was taken using a
popular thermistor model, the Betatherm 10K3A1, with
R
EXT
Fan-Speed Controllers with Thermistor Inputs
= 1.6kΩ. Using these values produces data with
-10
-12
-2
-4
-6
-8
4
2
0
0
Applications Information
T
1
______________________________________________________________________________________
Dual-Channel Temperature Monitors and
20
=
MAX6615/MAX6616 ERROR
A B In R
Thermistor Considerations
OPTIMIZED FOR +30°C TO +100°C
+
40
TEMPERATURE (°C)
60
( )
80
+
C In R
[ ( )]
100
120
3
140
good conformance to real temperature over a range of
about +30°C to +100°C. Different combinations of ther-
mistors and R
The integrating ADC has inherently good noise rejec-
tion, especially at low-frequency signals such as
60Hz/120Hz power-supply hum. Lay out the PCB care-
fully with proper external noise filtering for high-accura-
cy thermistor measurements in electrically noisy
environments.
Filter high-frequency electromagnetic interference
(EMI) at TH_ and REF with an external 100pF capacitor
connected between the two inputs. This capacitor can
be increased to about 2000pF (max), including cable
capacitance. A capacitance higher than 2000pF intro-
duces errors due to the rise time of the switched cur-
rent source.
PROCESS: BiCMOS
Figure 10. Measured Temperature vs. Actual Temperature
120
100
80
60
40
20
0
EXT
-50
MEASUREMENT vs. TEMPERATURE
result in different curves.
0
TEMPERATURE (°C)
Chip Information
50
ADC Noise Filtering
100
150
17