TC648 datasheet(5/28 Pages) MICROCHIP

5 / 28 page

 2002 Microchip Technology Inc.

DS21448C-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 (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 (see Section 5.0, “Typical

Applications”, for more 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. During shutdown, supply

current falls to 25 µA (typical). 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

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 VIN > VOTF

(see Section 1.0, "Electrical Characteristics"). An over-

temperature indication is a non-latching condition.

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

No Internal Connection

6OTF

Digital (Open Collector) Output

7VOUT

Digital Output

8VDD

Power Supply Input

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