Datasheet

 2001-2012 Microchip Technology Inc. DS21448D-page 5
TC648
2.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1: PIN FUNCTION TABLE
2.1 Analog Input (V
IN
)
The thermistor network (or other temperature sensor)
connects to the V
IN
input. A voltage range of 1.25V to
2.65V (typical) on this pin drives an active duty cycle of
0% to 100% on the V
OUT
pin (see Section 5.0, “Typical
Applications”, for more details).
2.2 Analog Output (C
F
)
C
F
is the positive terminal for the PWM ramp generator
timing capacitor. The recommended C
F
is 1 µF for
30 Hz PWM operation.
2.3 Analog Input (V
AS
)
An external resistor divider connected to the V
AS
input
sets the auto-shutdown threshold. Auto-shutdown
occurs when V
IN
 V
AS
. During shutdown, supply
current falls to 25 µA (typical). The fan is automatically
restarted when V
IN
 (V
AS
+V
HAS
) (see Section 5.0,
“Typical Applications” for more details).
2.4 Ground (GND)
GND denotes the ground Terminal.
2.5 No Connect
No internal connection.
2.6 Digital Output (OTF)
OTF goes low to indicate an over-temperature
condition. This occurs when the voltage at V
IN
> V
OTF
(see Section 1.0, "Electrical Characteristics"). An over-
temperature indication is a non-latching condition.
2.7 Digital Output (V
OUT
)
V
OUT
is an active high complimentary output that drives
the base of an external NPN transistor (via an appropri-
ate base resistor) or the gate of an N-channel MOS-
FET. This output has asymmetrical drive (see
Section 1.0, “Electrical Characteristics”).
2.8 Power Supply Input (V
DD
)
V
DD
may be independent of the fan’s power supply
(see Section 1.0, “Electrical Characteristics”).
Pin No. Symbol Description
1V
IN
Analog Input
2C
F
Analog Output
3V
AS
Analog Input
4 GND Ground Terminal
5 NC No Internal Connection
6OTF
Digital (Open Collector) Output
7V
OUT
Digital Output
8V
DD
Power Supply Input