 2003 Microchip Technology Inc.

DS21688C-page 5

TC670

3.0

PIN DESCRIPTIONS

The descriptions of the pins are listed in Table 3-1.

TABLE 3-1:

PIN FUNCTION TABLE

3.1

Analog Input (THRESHOLD)

The voltage set at the THRESHOLD input represents

the fan speed at which the TC670 will signal a fan

speed warning by pulling the ALERT output low. The

threshold voltage to fan speed correlation can be seen

in Figures 2-2 and 2-3.

3.2

Ground (GND)

The GND pin (Pin 2) of the TC670 should be connected

directly to the analog ground plane of the circuit board.

Care should be taken to keep this pin away from

switching signals, such as the fan excitation signals in

order to avoid false signals on the SENSE pin.

3.3

Digital Input (CLEAR)

The CLEAR input is used to reset or blank the ALERT

output. When the CLEAR input is driven high, the

ALERT output will be high-impedance (the ALERT

output requires a pull-up resistor).

3.4

Bias Supply Input, 3.0V to 5.5V. The bias supply input

should be bypassed to ground with a 0.1 µF ceramic

capacitor.

3.5

Digital (Open-Drain) Output

(ALERT)

The ALERT output is an open-drain output that

requires an external pull-up resistor. The ALERT output

is pulled low when the sensed fan speed (detected by

the pulses occurring at the SENSE input) falls below

the speed that is represented by the voltage at the

THRESHOLD pin. The ALERT output is latched in this

state until power is cycled or the CLEAR input is

toggled.

3.6

Analog Input (SENSE)

Voltage pulses, which are generated by the fan current

flowing through a sense resistor, are detected at the

SENSE pin and used to calculate the fan speed.

Pin

No.

Symbol

Description

1

THRESHOLD Analog Input

2

GND

Ground Terminal

3

CLEAR

Digital Input

Bias Supply Input

5ALERT

Digital (Open-Drain) Output

6

SENSE

Analog Input