TC664 datasheet(9/36 Pages) MICROCHIP

9 / 36 page

 2002 Microchip Technology Inc.

DS21737A-page 9

TC664/TC665

4.0

DEVICE OPERATION

The TC664/TC665 devices allow you to control, moni-

tor and communicate (via SMBus) fan speed for 2-wire

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

ing (PWM) the voltage across the fan, the TC664/

TC665 controls fan speed according to the system tem-

perature.The goal of temperature proportional fan

speed control is to reduce fan power consumption,

increase fan life and reduce system acoustic noise.

With the TC664/TC665 devices, fan speed can be con-

trolled by the analog input VIN or the SMBus interface,

allowing for high system flexibility.

The TC664/TC665 devices 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 TC664/TC665

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 TC664/TC665 devices are identical in every

aspect except for how they indicate an over-tempera-

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

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

FAULT output low during an over-temperature

condition.

FIGURE 4-1:

Typical Application Circuit.

+5 V

FAN

RISO

RSENSE

CSENSE

NTC Thermistor

0.01 µF

1µF

100 k

Ω @ 25°C

PICmicro®

Microcontroller

+12 V

+5 V

34.8 k

Ω

14.7 k

Ω

1.0 µF

RSCLK

20 k

Ω

RSDA

20 k

Ω

715

Ω

0.1 µF

RFAULT

20 k

Ω

Note: Refer to Table 7-1 for RSENSE value.

VIN

SCLK

SDA

GND

FAULT

SENSE

VOUT

VDD

TC664

TC665

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