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TC652/TC653
3.0
DETAILED DESCRIPTION
TABLE 3-2:
TEMPERATURE RANGE
The TC652/TC653 acquire and convert their junction
temperature (T J ) information from an on-chip solid
DEFINITION FOR TC653
(AUTO-SHUTDOWN MODE)
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
(T = T J )
T < T L
T L < = T < T 1
T 1 < = T < T 2
T 2 < =T < T 3
T 3 < =T < T 4
T 4 < = T < T H
T H < = T < T OV
T OV < = T
PWM Duty Cycle
“OFF”
50%
60%
70%
80%
90%
100%
100% with Over-Temp Alert
(T OVER = L)
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
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 .
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
FIGURE 3-1:
FUNCTIONAL BLOCK
DIAGRAM
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.
V DD
Temperature
Set Point and
T OVER
SHDN
Duty Cycle
Logic
V+
-
TABLE 3-1:
TEMPERATURE RANGE
Trim Range
Control
PWM
DEFINITION FOR TC652
(MINIMUM-SPEED MODE)
AD Converter
Oscillator
Temperature
(T = T J )
T < T L
T L < = T < T 1
T 1 < = T < T 2
PWM Duty Cycle
40%
50%
60%
Temp Sensor
Fan Detect
Logic
+
CMPTR
-
90mV
-
20k
FAULT
T 2 < = T <T 3
T 3 < = T < T 4
T 4 < = T < T H
70%
80%
90%
T H < = T < T OV
100%
3.1
PWM Output
T OV < = T
100% with Over-Temp Alert
(T OVER = L)
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.
2002 Microchip Technology Inc.
DS21453B-page 5
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