DTC646 datasheet(5/30 Pages) MICROCHIP

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 2002-2012 Microchip Technology Inc.

DS21446D-page 5

TC646

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 (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.

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”).

Pin No.

Symbol

Description

1VIN

Analog Input

2CF

Analog Output

3VAS

Analog Input

GND

Ground Terminal

SENSE

Analog Input

6FAULT

Digital (Open Collector) Output

7VOUT

Digital Output

8VDD

Power Supply Input

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