TC664EUNTR Microchip Technology, TC664EUNTR Datasheet - Page 23

• Manufacturer Part Number: TC664EUNTR
• Description: IC PWM FAN SPEED CONTRLR 10-MSOP
• Manufacturer: Microchip Technology
• Type: Controller - SMBus Fan Speedr

Specifications of TC664EUNTR

• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 300 uA
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

7.3
As discussed in previous sections, the V
has a range of 1.62 V to 2.6 V (typical), which repre-
sents a duty cycle range on the V
100%, respectively. The V
as representing temperatures. The 1.62 V level is the
low temperature at which the system only requires 30%
fan speed for proper cooling. The 2.6 V level is the high
temperature, for which the system needs maximum
cooling capability, so the fan needs to be at 100%
speed.
One of the simplest ways of sensing temperature over
a given range is to use a thermistor. By using an NTC
thermistor as shown in Figure 7-3, a temperature vari-
ant voltage can be created.
FIGURE 7-3:
Circuit.
Figure 7-3 represents a temperature dependent volt-
age divider circuit. R
R
allel resistor combination that will be referred to as
R
increases, the value of R
R
V
desired relationship for the V
R
work. Figure 7-4 shows an example of this.
There are many values that can be chosen for the NTC
thermistor. There are also thermistors that have a linear
resistance, instead of logarithmic, which can help to
eliminate R
then a larger value thermistor should be chosen. The
voltage at the V
age output temperature sensor device. The key is to
get the desired V
temperature relationship.
The following equations apply to the circuit in
Figure 7-3.
IN
1
TEMP
TEMP
1
2002 Microchip Technology Inc.
and R
is to help linearize the response of the sensing net-
increases as temperature increases, giving the
(R
will decrease with it. Accordingly, the voltage at
Temperature Sensor Design
2
TEMP
are standard resistors. R
R
1
t
. If less current draw from V
= R
IN
IN
pin can also be generated by a volt-
1
voltage to system (or component)
t
* R
is a conventional NTC thermistor,
Temperature Sensing
t
/ R
V
t
IN
DD
decreases and the value of
1
voltages can be thought of
R
R
+ R
I
IN
1
2
DIV
input. The purpose of
t
). As the temperature
OUT
1
and R
output of 30% to
IN
V
DD
IN
analog input
t
form a par-
is desired,
EQUATION
In order to solve for the values of R
for V
occur, need to be selected. The variables, t1 and t2,
represent the selected temperatures. The value of the
thermistor at these two temperatures can be found in
the thermistor data sheet. With the values for the ther-
mistor and the values for V
tions from which the values for R
Example: The following design goals are desired:
• Duty Cycle = 50% (V
• Duty Cycle = 100% (V
Using a 100 k thermistor (25°C value), we look up the
thermistor values at the desired temperatures:
• R
• R
Substituting these numbers into the given equations,
we come up with the following numbers for R
• R
• R
FIGURE 7-4:
V
Figure 7-4 graphs three parameters versus tempera-
ture. They are R
described earlier, you can see that the thermistor has a
logarithmic resistance variation. When put in parallel
with R
more linear, which is the desired effect. This gives us
the linear looking curve for V
IN
(t1) = 30°C
ture (t2) = 60°C
, And R
t
t
1
2
= 79428
= 22593
IN,
= 34.8 k
= 14.7 k
140000
120000
100000
1
80000
60000
40000
20000
, though, the combined resistance becomes
and the temperatures at which they are to
0
TEMP
R
TEMP
V t1
V t2
@ 30°C
@ 60°C
t
, R
Vary With Temperature.
TC664/TC665
Temperature (ºC)
=
=
1
How Thermistor Resistance,
IN
in parallel with R
V
--------------------------------------- -
R
--------------------------------------- -
R
IN
IN
TEMP
TEMP
= 1.9 V) with Temperature
Voltage
IN
= 2.6 V) with Tempera-
V
V
D D
D D
, you now have two equa-
IN
NTC Thermistor
100K @ 25ºC
.
t1
t2
1
and R
R
R
1
+
+
2
2
and R
DS21737A-page 23
R
R
2
2
2
t
can be found.
, and V
2
, the values
4.000
3.500
3.000
2.500
2.000
1.500
1.000
0.500
0.000
1
and R
IN
. As
2
.