Datasheet
2002-2012 Microchip Technology Inc. DS21452C-page 5
TC652/TC653
3.0 DETAILED DESCRIPTION
The TC652/TC653 acquire and convert their junction
temperature (T
J
) information from an on-chip solid
state sensor with a typical accuracy of ±1°C. The
temperature data is digitally stored in an internal
register. The register is compared with pre-defined
threshold values. The six threshold values are equally
distributed over a pre-defined range of temperatures
(See Table 3-1 and Table 3-2). The TC652/TC653
control the speed of a DC brushless fan using a
fractional speed control scheme. The output stage
requires only a 2N2222-type small-signal BJT for fans
up to 300mA. For larger current fans (up to 1 Amp) a
logic-level N-channel MOSFET may be used. In
addition to controlling the speed of the fan, the TC652/
TC653 include an on-chip over-temperature alarm
(T
OVER
) that gives a low-true signal when the
temperature of the chip exceeds T
H
by 10°C. This
feature eliminates the need for a separate temperature
sensor for over-temperature monitoring.
In normal fan operation, a pulse-train is present at
SENSE, Pin 5. A Missing Pulse Detector monitors this
pin during fan operation (FanSense
™ technology). A
stalled, open, or unconnected fan causes the TC652/
TC653 to trigger its Start-up Timer once. If the FAULT
persists, the FAULT
output goes low, and the device is
latched in its Shutdown mode. To release the fan from
shutdown, toggle the SHDN or V
DD
pin.
TABLE 3-1: TEMPERATURE RANGE
DEFINITION FOR TC652
(MINIMUM-SPEED MODE)
TABLE 3-2: TEMPERATURE RANGE
DEFINITION FOR TC653
(AUTO-SHUTDOWN MODE)
FIGURE 3-1: FUNCTIONAL BLOCK
DIAGRAM
3.1 PWM Output
The PWM pin is designed to drive a low cost transistor
or MOSFET as the low side power switching element in
the system. This output has an asymmetric
complementary drive and is optimized for driving NPN
transistors or N-channel MOSFETs. Since the system
relies on PWM rather than linear power control, the
dissipation in the power switch is kept to a minimum.
Generally, very small devices (TO-92 or SOT
packages) will suffice. The frequency of the PWM is
about 15Hz. The PWM is also the time base for the
Start-up Timer (see paragraphs below). The PWM duty
cycle has a range of 40% to 100% for the TC652 and
50% to 100% for the TC653.
Temperature
(T = T
J
)
PWM Duty Cycle
T < T
L
40%
T
L
< = T < T
1
50%
T
1
< = T < T
2
60%
T
2
< = T <T
3
70%
T
3
< = T < T
4
80%
T
4
< = T < T
H
90%
T
H
< = T < T
OV
100%
T
OV
< = T 100% with Over-Temp Alert
(T
OVER
= L)
Temperature
(T = T
J
)
PWM Duty Cycle
T < T
L
“OFF”
T
L
< = T < T
1
50%
T
1
< = T < T
2
60%
T
2
< =T < T
3
70%
T
3
< =T < T
4
80%
T
4
< = T < T
H
90%
T
H
< = T < T
OV
100%
T
OV
< = T 100% with Over-Temp Alert
(T
OVER
= L)
Note: The temperature regions defined by the six tempera-
ture thresholds are pre-defined in the TC650/651 by means
of trimming. Once a T
L
and T
H
are programmed, the T
1
- T
4
thresholds are automatically equally spaced between T
L
and
T
H
.
Temp Sensor
Fan Detect
Logic
Duty Cycle
Logic
Control
AD Converter
Oscillator
Temperature
Set Point and
Trim Range
SHDN
T
OVER
PWM
FAULT
90mV
V
DD
V+
CMPTR
+
-
20k
-
-