TC647BEOATR datasheet(10/34 Pages) MICROCHIP

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TC642B/TC647B

DS21756B-page 10

 2003 Microchip Technology Inc.

3.0

PIN FUNCTIONS

The description 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.

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 (VMIN)

An external resistor divider connected to VMIN sets the

minimum fan speed by fixing the minimum PWM duty

cycle (1.20V to 2.60V = 0% to 100%, typical). The

TC642B and TC647B devices enter shutdown mode

when 0

≤ VMIN ≤ VSHDN. During shutdown, the FAULT

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)

The FAULT line goes low to indicate a fault condition.

When FAULT goes low due to a fan fault, 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 TC642B device, the FAULT

output will also be asserted when the VIN voltage

reaches the VOTF treshold 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 and

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.

Name

Function

1VIN

Analog Input

2CF

Analog Output

3VMIN

Analog Input

GND

Ground

SENSE

Analog Input

6FAULT

Digital (Open-Drain) Output

7VOUT

Digital Output

8VDD

Power Supply Input

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