TC642
DS21444D-page 16 2001-2012 Microchip Technology Inc.
5.8 TC642 as a Microcontroller
Peripheral
In a system containing a microcontroller or other host
intelligence, the TC642 can be effectively managed as
a CPU peripheral. Routine fan control functions can be
performed by the TC642 without processor intervention.
The microcontroller receives temperature data from one
or more points throughout the system. It calculates a fan
operating speed based on an algorithm specifically
designed for the application at hand. The processor
controls fan speed using complementary port bits I/O1
through I/O3. Resistors R
1
through R
6
(5% tolerance)
form a crude 3-bit DAC that translates the 3-bit code
from the processor's outputs into a 1.6V DC control sig-
nal. A monolithic DAC or digital pot may be used
instead of the circuit shown in Figure 5-10.
With V
MIN
set to 1.8V, the TC642 has a minimum
operating speed of approximately 40% of full rated
speed when the processor's output code is 000[B].
Output codes 001[B] to 111[B] operate the fan from
roughly 40% to 100% of full speed. An open-drain
output from the processor (I/O0) can be used to reset
the TC642 following detection of a fault condition. The
FAULT
output can be connected to the processor's
interrupt input, or to an I/O pin, for polled operation.
FIGURE 5-10: TC642 as a Microcontroller Peripheral.
TC642
V
IN
C
F
V
MIN
GND
V
DD
V
OUT
FAULT
SENSE
(Optional)
(MSB)
R
1
110 kΩ
R
2
240 kΩ
R
3
360 kΩ
(LSB)
R
5
1.5 kΩ
+5V
R
6
1 kΩ
R
4
18 kΩ
R
7
33 kΩ
+5V
R
8
18 kΩ
C
B
.01 μF
+
1 μF
C
B
.01 μF
Fan
+12V
+5V
C
B
1 μF
+
800Ω
+5V
R
10
10 kΩ
0.1 μF
2N2222A
R
11
2.2Ω
1
2
3
4
5
6
7
8
(RESET)
CMOS
Microcontroller
+5V
Analog or Digital
Temperature
Data from one or
more Sensors
I/O0
I/O1
I/O2
I/O3
INT
GND
CMOS
Outputs
Open-drain
Outputs
R
9