Datasheet

 2001-2012 Microchip Technology Inc. DS21448D-page 15
TC648
FIGURE 5-8: Design Example.
5.8 TC648 as a Microcontroller
Peripheral
In a system containing a microcontroller or other host
intelligence, the TC648 can be effectively managed as
a CPU peripheral. Routine fan control functions can be
performed by the TC648 without processor interven-
tion. 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 signal. A
monolithic DAC or digital pot may be used instead of
the circuit shown in Figure 5-9.
With V
AS
set at 1.8V, the TC648 enters auto-shutdown
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 TC648
following detection of a fault condition. The OTF
output
can be connected to the processor's interrupt input, or
to another I/O pin, for polled operation.
NC
NTC
10 kΩ
@ 25˚C
R
1
20.5 kΩ
R
2
3.83 kΩ
R
5
33 kΩ
R
7
800Ω
R
6
GND
RESET
Shutdown
(Optional)
Q
1
+12V
+5V
+5V
+5V
V
DD
V
IN
V
AS
V
OUT
C
B
1 μF
C
F
TC648
OTF
Fan
Thermal
Fault
C
B
0.01 μF
C
B
0.01 μF
C
B
1 μF
1
8
4
6
7
5
2
3
18 kΩ
Open-Drain
Device