TC648BEOA Microchip Technology, TC648BEOA Datasheet - Page 24

• Manufacturer Part Number: TC648BEOA
• Description: IC PWM FAN SPEED CTRLR SD 8-SOIC
• Manufacturer: Microchip Technology
• Type: Controller - PWM Fanr

Specifications of TC648BEOA

• 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: 8-SOIC (3.9mm Width)
• Motor Type: PWM
• No. Of Outputs: 1
• Output Current: 5mA
• Output Voltage: 4.4V
• Supply Voltage Range: 3V To 5.5V
• Driver Case Style: SOIC
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +85°C
• Product: Fan / Motor Controllers / Drivers
• Operating Supply Voltage: 3 V to 5.5 V
• Supply Current: 400 uA
• Mounting Style: SMD/SMT
• 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

TC646B/TC648B/TC649B
Step 2: Selecting the Fan Controller.
The requirements for the fan controller are that it have
auto-shutdown capability at 20ºC and also indicate a
fan fault condition. No over-temperature indication is
necessary. From these specifications, the proper
selection is the TC649B device.
Step 3: Setting the PWM Frequency.
The fan is rated at 4200 RPM with a 12V input. The
goal is to run to a 40% duty cycle (roughly 40% fan
speed), which equates to approximately 1700 RPM. At
1700 RPM, one full fan revolution occurs every
35 msec. The fan being used is a four-pole fan that
gives four current pulses per revolution. With this infor-
mation, and viewing test results at 40% duty cycle, two
fan current pulses were always seen during the PWM
on time with a PWM frequency of 30 Hz. For this rea-
son, the C
Step 4: Setting the V
From the design criteria, the desired duty cycle at 20ºC
is 40% and 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 along with the thermistor resistance
values calculated earlier, the R
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
DS21755B-page 24
TEMP
- 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
F
value is selected to be 1.0 µF.
IN
V T1
V T2
V
voltage range of 1.20V to 2.60V, which
IN
= (DC * 1.4V) + 1.20V
IN
=
=
Voltage.
IN
----------------------------------------- -
R
----------------------------------------- -
R
TEMP
TEMP
voltage at 40ºC. Solving the
V
V
DD
DD
1
IN
T1
T2
and R
voltage at 20ºC and
R
R
2
+
2
+
R
R
2
IN
2
2
1
resistor values
and the ther-
values are
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 Auto-Shutdown Voltage (V
Setting the voltage for the auto-shutdown is done using
a simple resistor voltage divider. The criteria for the
voltage divider in this design is that it draw no more
than 100 µA of current. The required auto-shutdown
voltage was determined earlier in the selection of the
V
at the temperature that auto-shutdown 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
Using standard 1% resistor values yields the following
values:
IN
TEMP
2
- R
- R
- V
- R
- R
- R
- R
values are:
voltage at 40% duty cycle, since this was also set
400
350
300
250
200
150
100
AS
4
1
2
3
4
3
4
50
TEMP
0
= 45.3 k
are found to be:
= 237 k
= 32.4 k
= 17.6 k
= 32.4 k
= 17.8 k
0
= 1.76V
resistance
R
10
TEMP
vs. Temperature
20
IN
V
I
30
voltage, thermistor resistance and
DIV
AS
Temperature (ºC)
versus
Thermistor Resistance, V
=
40
NTC Thermistor
100 k @ 25ºC
=
2003 Microchip Technology Inc.
R
R
50
5V * R
3
3
5V
+ R
+ R
60
temperature
V
IN
4
3
4
4
70
and R
80
4
:
90
5.00
4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
for
AS
).
1
and
this
IN
3