TC654T datasheet(9/38 Pages) MICROCHIP

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 2002-2014 Microchip Technology Inc.

DS20001734C-page 9

TC654/TC655

4.0

DEVICE OPERATION

The TC654 and TC655 devices allow you to control,

monitor and communicate (via SMBus) fan speed for 2-

wire and 3-wire DC brushless fans. By pulse-width

modulating (PWM) the voltage across the fan, the

TC654/TC655 controls fan speed according to the sys-

tem temperature.The goal of temperature proportional

fan speed control is to reduce fan power consumption,

increase fan life and reduce system acoustic noise.

With the TC654 and TC655 devices, fan speed can be

controlled by the analog input VIN or the SMBus inter-

face, allowing for high system flexibility.

The TC654 and TC655 also measure and monitor fan

revolutions per minute (RPM). A fan’s speed (RPM) is

a measure of its health. As a fan’s bearings wear out,

the fan slows down and eventually stops (locked rotor).

By monitoring the fan’s RPM level, the TC654/TC655

devices can detect open, shorted, unconnected and

locked rotor fan conditions. The fan speed threshold

can be set to provide a predictive fan failure feature.

This feature can be used to give a system warning and,

in many cases, help to avoid a system thermal shut-

down condition. The fan RPM data and threshold reg-

isters are available over the SMBus interface which

allows for complete system control.

The TC654/TC655 devices are identical in every

aspect except for how they indicate an over-tempera-

ture condition. When VIN voltage exceeds 2.6V (typi-

cal), both devices will set OTF (bit 5<X>) in the Status

FAULT output low during an over-temperature condi-

tion.

FIGURE 4-1:

Typical Application Circuit.

VIN

SCLK

SDA

GND

FAULT

SENSE2

SENSE1

VOUT

VDD

+5V

FAN

RISO1

RISO2

RSENSE2

RSENSE1

CSENSE2

CSENSE1

NTC Thermistor

0.01 µF

1µF

100 k

 @ 25°C

PIC®

Microcontroller

+12V

+5V

34.8 k



14.7 k



1.0 µF

RSCLK

20 k



RSDA

20 k



715



0.1 µF

715



RFAULT

20 k



Note: Refer to Table 7-1 for RSENSE1 and RSENSE2 values.

TC654/TC655

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