Datasheet

 2002-2013 Microchip Technology Inc. DS21737B-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 V
IN
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 V
IN
voltage exceeds 2.6 V (typi-
cal), both devices will set OTF (bit 5<X>) in the Status
Register to a '1'. The TC665 will additionally pull the
FAULT
output low during an over-temperature
condition.
FIGURE 4-1: Typical Application Circuit.
1
2
3
4
5
6
7
8
9
10
+5 V
FAN
R
ISO
R
SENSE
C
SENSE
NTC Thermistor
R
1
R
2
C
1
0.01 µF
C
2
1µF
100 k @ 25°C
PIC
®
Microcontroller
+12 V
+5 V
+5 V
+5 V
34.8 k
14.7 k
C
F
1.0 µF
R
SCLK
20 k
R
SDA
20 k
715 
0.1 µF
R
FAULT
20 k
Note: Refer to Table 7-1 for R
SENSE
value.
V
IN
C
F
SCLK
SDA
GND
FAULT
NC
SENSE
V
OUT
V
DD
TC664
TC665