TC642BEPA Microchip Technology, TC642BEPA Datasheet - Page 23

• Manufacturer Part Number: TC642BEPA
• Description: IC PWM FAN SPEED CTRLR 8-DIP
• Manufacturer: Microchip Technology
• Type: PWM Fan Speed Controllerr

Specifications of TC642BEPA

• Applications: Fan Controller, Brushless (BLDC)
• Number Of Outputs: 1
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Motor Type: PWM
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: DIP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 6 V
• Supply Current: 400 uA
• Mounting Style: Through Hole
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Step 2: Selecting the Fan Controller.
The requirements for the fan controller are that it have
minimum speed capability at 20ºC and also indicate a
fan fault condition. No over-temperature indication is
necessary. Based on these specifications, the proper
selection is the TC647B device.
Step 3: Setting the PWM Frequency.
The fan is rated at 4200 RPM with a 12V input. Since
the goal is to run to a 40% duty cycle (roughly 40% fan
speed), which equates to approximately 1700 RPM,
we can assume one full fan revolution occurs every
35 msec. The fan being used is a four-pole fan that
gives four current pulses per revolution. Knowing this
and viewing test results at 40% duty cycle, two fan cur-
rent pulses were always seen during the PWM on time
with a PWM frequency of 30 Hz. For this reason, the C
value is selected to be 1.0 F.
Step 4: Setting the V
From the design criteria, the desired duty cycle at 20ºC
is 40%, while full fan speed should be reached at 40ºC.
Based on a V
represents 0% to 100% duty cycle, the 40% duty cycle
voltage can be found using the following equation:
EQUATION
Using the above equation, the V
calculated to be:
Using these values in combination with the thermistor
resistance values calculated earlier, the R
resistor values can now be calculated using the
following equation:
EQUATION
R
mistor. V(T1) represents the V
V(T2) represents the V
equations simultaneously yields the following values
(V
TEMP
2003 Microchip Technology Inc.
- V
- V
DD
- R
- R
DC = Desired Duty Cycle
= 5V):
IN
IN
1
2
is the parallel combination of R
= 238,455
= 45,161
(40%) = 1.76V
(100%) = 2.60V
IN
V T1
V T2
V
voltage range of 1.20V to 2.60V, which
IN
= (DC * 1.4V) + 1.20V
IN
=
=
IN
Voltage.
----------------------------------------- -
R
----------------------------------------- -
R
TEMP
TEMP
voltage at 40ºC. Solving the
V
V
DD
DD
IN
T1
T2
voltage at 20ºC and
R
R
2
+
2
+
R
R
IN
2
2
1
and the ther-
values are
1
and R
F
2
Using standard 1% resistor values, the selected R
R
A graph of the V
R
configuration is shown in Figure 5-10.
FIGURE 5-10:
and R
Step 5: Setting the Minimum Speed Voltage (V
Setting the voltage for the minimum speed is accom-
plished using a simple resistor voltage divider. The cri-
teria for the voltage divider in this design is that it draw
no more than 100 µA of current. The required minimum
speed voltage was determined earlier in the selection
of the V
set at the temperature which minimum speed is to
occur (20ºC).
Given this desired setpoint, and knowing the desired
divider current, the following equations can be used to
solve for the resistor values for R
EQUATION
Using the equations above, the resistor values for R
and R
2
TEMP
- R
- R
- V
- R
- R
values are:
400
350
300
250
200
150
100
50
MIN
4
1
2
0
3
4
TEMP
IN
= 237 k
= 45.3 k
0
are found to be:
= 32.4 k
= 17.6 k
resistance
voltage at 40% duty cycle, since this was also
= 1.76V
R
10
TEMP
TC642B/TC647B
vs. Temperature.
20
IN
V
30
I
voltage, thermistor resistance and
DIV
MIN
Temperature (ºC)
versus
Thermistor Resistance, V
40
NTC Thermistor
100 k @ 25ºC
=
=
R
R
50
5V*R
3
3
5V
+ R
+ R
temperature
60
V
IN
4
4
3
4
and R
70
DS21756B-page 23
80
4
:
90
for
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
MIN
1
).
and
this
IN
,
3