TC646 View Datasheet(PDF) - Microchip Technology
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TC646 Datasheet PDF : 28 Pages
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2.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1: PIN FUNCTION TABLE
Pin No. Symbol
Description
1
VIN Analog Input
2
CF Analog Output
3
VAS Analog Input
4
GND Ground Terminal
5
SENSE Analog Input
6
FAULT Digital (Open Collector) Output
7
VOUT Digital Output
8
VDD Power Supply Input
2.1 Analog Input (VIN)
The thermistor network (or other temperature sensor)
connects to the VIN 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 VOUT pin. The TC646 enters shut-
down mode when VIN ≤ VSHDN. During shutdown, the
FAULT output is inactive, and supply current falls to
25 µA (typical). The TC646 exits shutdown mode
when VIN ≥ VREL (see Section 5.0, “Typical
Applications”, for details).
2.2 Analog Output (CF)
CF is the positive terminal for the PWM ramp generator
timing capacitor. The recommended CF is 1 µF for
30 Hz PWM operation.
TC646
2.3 Analog Input (VAS)
An external resistor divider connected to the VAS input
sets the auto-shutdown threshold. Auto-shutdown
occurs when VIN ≤ VAS. The fan is automatically
restarted when VIN ≥ (VAS + VHAS) (see Section 5.0,
“Typical Applications”, for more details).
2.4 Ground (GND)
GND denotes the ground terminal.
2.5 Analog Input (SENSE)
Pulses are detected at the SENSE pin as fan rotation
chops the current through a sense resistor (RSENSE).
The absence of pulses indicates a fault (see
Section 5.0, “Typical Applications”, for more details).
2.6 Digital Output (FAULT)
The FAULT line goes low to indicate a fault condition.
When FAULT goes low due to a fan fault condition, the
device is latched in shutdown mode until deliberately
cleared or until power is cycled. FAULT will also be
asserted when the PWM reaches 100% duty cycle,
indicating that maximum cooling capability has been
reached and a possible over-temperature condition
may occur. This is a non-latching state and the FAULT
output will go high when the PWM duty cycle goes
below 100%.
2.7 Digital Output (VOUT)
VOUT 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 (VDD)
VDD may be independent of the fan’s power supply
(see Section 1.0, “Electrical Characteristics”).
2002 Microchip Technology Inc.
DS21446C-page 5
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