TC648BEPATR datasheet(10/36 Pages) MICROCHIP

10 / 36 page

TC646B/TC648B/TC649B

DS21755B-page 10

 2003 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 (VIN)

The thermistor network (or other temperature sensor)

connects to VIN. 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 VOUT pin. The TC646B, TC648B and

TC649B

devices

enter

shutdown

mode

when

≤ VIN ≤ VSHDN. During shutdown, the FAULT/OTF

output is inactive and supply current falls to 30 µA

(typical).

3.2

Analog Output (CF)

CF is the positive terminal for the PWM ramp generator

timing capacitor. The recommended value for the CF

capacitor is 1.0 µF for 30 Hz PWM operation.

3.3

Analog Input (VAS)

An external resistor divider connected to VAS sets the

auto-shutdown threshold. Auto-shutdown occurs when

VIN < VAS. The fan is automatically restarted when

VIN > (VAS + VHAS). 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 VIN voltage reaches

the VOTF threshold of 2.62V (typical). This gives an

over-temperature/100% fan speed indication.

3.6

Digital Output (VOUT)

VOUT 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 VOUT output is continuously on.

3.7

Power Supply Input (VDD)

The VDD 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.

Name

Function

1VIN

Analog Input

2CF

Analog Output

3VAS

Analog Input

GND

Ground

SENSE/NC

Analog Input/No Connect. NC for TC648B.

6FAULT/OTF

Digital (Open-Drain) Output

OTF for TC648B

7VOUT

Digital Output

8VDD

Power Supply Input

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