Datasheet

TC646B/TC648B/TC649B
DS21755C-page 10  2002-2013 Microchip Technology Inc.
3.0 PIN FUNCTIONS
The descriptions of the pins are given in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
3.1 Analog Input (V
IN
)
The thermistor network (or other temperature sensor)
connects to V
IN
. A voltage range of 1.20V to 2.60V (typ-
ical) on this pin drives an active duty cycle of 0% to
100% on the V
OUT
pin. The TC646B, TC648B and
TC649B devices enter shutdown mode when
0  V
IN
 V
SHDN
. During shutdown, the FAULT/OTF
output is inactive and supply current falls to 30 µA
(typical).
3.2 Analog Output (C
F
)
C
F
is the positive terminal for the PWM ramp generator
timing capacitor. The recommended value for the C
F
capacitor is 1.0 µF for 30 Hz PWM operation.
3.3 Analog Input (V
AS
)
An external resistor divider connected to V
AS
sets the
auto-shutdown threshold. Auto-shutdown occurs when
V
IN
< V
AS
. The fan is automatically restarted when
V
IN
> (V
AS
+ V
HAS
). During auto-shutdown, the
FAULT/OTF output is inactive and supply current falls
to 30 µA (typical).
3.4 Analog Input (SENSE)
Pulses are detected at SENSE as fan rotation chops
the current through a sense resistor. The absence of
pulses indicates a fan fault condition.
3.5 Digital (Open-Drain) Output
(
FAULT
/OTF
)
FAULT/OTF goes low to indicate a fault condition.
When FAULT
goes low due to a fan fault (TC646B and
TC649B devices), the output will remain low until the
fan fault condition has been removed (16 pulses have
been detected at the SENSE pin in a 32/f period). For
the TC646B and TC648B devices, the FAULT
/OTF out-
put will also be asserted when the V
IN
voltage reaches
the V
OTF
threshold of 2.62V (typical). This gives an
over-temperature/100% fan speed indication
.
3.6 Digital Output (V
OUT
)
V
OUT
is an active-high complimentary output that
drives the base of an external NPN transistor (via an
appropriate base resistor) or the gate of an N-channel
MOSFET. This output has asymmetrical drive. During a
fan fault condition, the V
OUT
output is continuously on.
3.7 Power Supply Input (V
DD
)
The V
DD
pin with respect to GND provides power to the
device. This bias supply voltage may be independent of
the fan power supply.
3.8 Ground (GND)
Ground terminal.
3.9 No Connect (NC)
No internal connection.
Pin Name Function
1V
IN
Analog Input
2C
F
Analog Output
3V
AS
Analog Input
4 GND Ground
5 SENSE/NC Analog Input/No Connect. NC for TC648B.
6FAULT
/OTF Digital (Open-Drain) Output
OTF
for TC648B
7V
OUT
Digital Output
8V
DD
Power Supply Input