21734C.book

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DS20001734C-page 1

TC654/TC655

Features:

• Temperature Proportional Fan Speed for Reduced 

Acoustic Noise and Longer Fan Life

• FanSense™ Protects against Fan Failure and 

Eliminates the Need for 3-wire Fans

• Overtemperature Detection (TC655)

• Efficient PWM Fan Drive

• Provides RPM Data

• 2-Wire SMBus™-Compatible Interface

• Supports Any Fan Voltage

• Software Controlled Shutdown Mode for "Green" 

Systems

• Supports Low-Cost NTC/PTC Thermistors

• Space Saving 10-Pin MSOP Package

• Temperature Range: -40°C to +85ºC

Applications:

• Personal Computers and Servers

• LCD Projectors

• Datacom and Telecom Equipment

• Fan Trays

• File  Servers

• Workstations

• General Purpose Fan Speed Control

Package Type

Description:

The TC654 and TC655 are PWM mode fan speed con-
trollers with FanSense technology for use with brush-
less DC fans. These devices implement temperature
proportional fan speed control which lowers acoustic
fan noise and increases fan life. The voltage at V

IN

(Pin 1) represents temperature and is typically pro-
vided by an external thermistor or voltage output tem-
perature sensor. The PWM output (V

OUT

) is adjusted

between 30% and 100%, based on the voltage at V

IN

.

The PWM duty cycle can also be programmed via
SMBus to allow fan speed control without the need for
an external thermistor. If V

IN

 is not connected, the

TC654/TC655 will start driving the fan at a default duty
cycle of 39.33%. See 

Section 4.3 “Fan Start-up”

 for

more details.

In normal fan operation, pulse trains are present at
SENSE1 (Pin 8) and SENSE2 (Pin 7). The TC654/
TC655 use these pulses to calculate the fan revolu-
tions per minute (RPM). The fan RPM data is used to
detect a worn out, stalled, open or unconnected fan.
An RPM level below the user-programmable threshold
causes the TC654/TC655 to assert a logic low alert
signal (FAULT). The default threshold value is
500 RPM. Also, if this condition occurs, F1F (bit 0<0>)
or F2F (bit 1<0>) in the Status Register will also be set
to a ‘1’.

An over-temperature condition is indicated when the
voltage at V

IN

 exceeds 2.6V (typical). The TC654/

TC655 devices indicate this by setting OTF(bit 5<X>) in
the Status Register to a '1'. The TC655 device also
pulls the FAULT line low during an over-temperature
condition. 

The TC654/TC655 devices are available in a 10-Pin
MSOP package and consume 150 µA during opera-
tion. The devices can also enter a low-power Shutdown
mode (5 µA, typ.) by setting the appropriate bit in the
Configuration Register. The operating temperature
range for these devices is -40°C to +85ºC.

10-Pin MSOP

1

2

3

4

5

10

9

8

7

6

V

IN

C

F

SCLK

SDA

GND

V

DD

V

OUT

SENSE1

SENSE2

FAULT

TC654
TC655

Dual SMBus™ PWM Fan Speed Controllers With

Fan Fault Detection

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TC654/TC655

DS20001734C-page 2

 2002-2014 Microchip Technology Inc.

Functional Block Diagram

V

OTF

50 k

OTF

V

MIN

TC654/TC655

SENSE1

FAULT

V

OUT

V

DD

GND

SDA

SCLK

C

F

V

IN

+

+

Clock

Generator

Serial Port

Interface

Control

Logic

Start-up

Timer

Missing

Pulse

Detect

100 mV (typ.)

50 k

SENSE2

100 mV (typ.)

+

Note: OTF condition applies for the TC655 device only.

Note

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DS20001734C-page 3

TC654/TC655

1.0

ELECTRICAL 
CHARACTERISTICS

Absolute Maximum Ratings *

V

DD

...................................................................................6.5V

Input Voltages  ...................................... -0.3V to (V

DD

 + 0.3V)

Output Voltages .................................... -0.3V to (V

DD

 + 0.3V) 

Storage temperature .....................................-65°C to +150°C

Ambient temp. with power applied ................-40°C to +125°C

Maximum Junction Temperature, T

J

............................. 150°C

ESD protection on all pins

4 kV

*Notice: Stresses above those listed under “Maximum rat-
ings” may cause permanent damage to the device. This is a
stress rating only and functional operation of the device at
those or any other conditions above those indicated in the
operational listings of this specification is not implied. Expo-
sure to maximum rating conditions for extended periods may
affect device reliability.

PIN FUNCTION TABLE

Name

Function

V

IN

Analog Input

C

F

Analog Output

SCLK

Serial Clock Input

SDA

Serial Data In/Out (Open Drain)

GND

Ground

FAULT

Digital (Open Drain) Output

SENSE2

Analog Input

SENSE1

Analog Input

V

OUT

Digital Output

V

DD

Power Supply Input

ELECTRICAL SPECIFICATIONS

Electrical Characteristics: Unless otherwise noted, all limits are specified for V

DD

 = 3.0V to 5.5V,

 -40°C <T

< +85°C.

Parameters

Sym.

Min.

Typ.

Max.

Units

Conditions

Supply Voltage

V

DD

3.0

5.5

V

Operating Supply Current

I

DD

150

300

µA

Pins 7, 8, 9 Open

Shutdown Mode Supply Current 

I

DDSHDN

5

10

µA

Pins 7, 8, 9 Open

V

OUT

 PWM Output

V

OUT

 Rise Time 

t

R

50

µsec

I

OH 

= 5 mA, 

Note 1

V

OUT

 Fall Time 

t

F

50

µsec

I

OL 

= 1 mA, 

Note 1

Sink Current at V

OUT

 Output

I

OL

1.0

mA

V

OL

 = 10% of V

DD

Source Current at V

OUT

 Output

I

OH

5.0

mA

V

OH

 = 80% of V

DD

PWM Frequency

F

26

30

34

Hz

C

F

 = 1 µF

V

IN 

Input

V

IN

 Input Voltage for 100% PWM 

duty-cycle 

V

C(MAX)

2.45

2.6

2.75

V

V

C(MAX)

 - V

C(MIN)

V

CRANGE

1.25

1.4

1.55

V

V

IN

 Input Resistance

10M

V

DD

 = 5.0V

V

IN

 Input Leakage Current

I

IN

-1.0

+1.0

µA

SENSE Input

SENSE Input Threshold Voltage with 
Respect to GND

V

THSENSE

80

100

120

mV

FAULT Output

FAULT Output LOW Voltage

V

OL

0.3

V

I

OL

 = 2.5 mA

FAULT Output Response Time 

t

FAULT

2.4

sec

Fan RPM-to-Digital Output

Fan RPM ERROR

-15

— 

+15

%

RPM > 1600

Note 1: Not production tested, ensured by design, tested during characterization.

2: For 5.0V > V

DD 

 5.5V, the limit for V

IH

 = 2.2V.

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TC654/TC655

DS20001734C-page 4

 2002-2014 Microchip Technology Inc.

TEMPERATURE SPECIFICATIONS

TIMING SPECIFICATIONS

2-Wire Serial Bus Interface

Logic Input High

V

IH

2.1

V

Note 2

Logic Input Low

V

IL

0.8

V

Logic Output Low

V

OL

0.4

V

I

OL

 = 3 mA

Input Capacitance SDA, SCLK

C

IN

10

15

pF

Note 1

I/O Leakage Current 

I

LEAK

-1.0

+1.0

µA

SDA Output Low Current

I

OLSDA

6

mA

V

OL

 = 0.6V

Electrical Characteristics: Unless otherwise noted, all parameters apply at V

DD

  =  3.0 V  to  5.5 V

Parameters

Symbol

Min

Typ

Max

Units

Conditions

Temperature Ranges

Specified Temperature Range

T

A

-40

+85

°C

Operating Temperature Range

T

A

-40

+125

°C

Storage Temperature Range

T

A

-65

+150

°C

Thermal Package Resistances

Thermal Resistance, 10 Pin MSOP

JA

113

°C/W

Electrical Characteristics: Unless otherwise noted, all limits are specified for V

DD

 = 3.0V to 5.5V,

-40°C <T

< +85°C

Parameters

Sym

Min

Typ

Max

Units

Conditions

SMBus Interface (See 

Figure 1-1

)

Serial Port Frequency

f

SC

0

100

kHz

Note 1

Low Clock Period

t

LOW

4.7

µsec

Note 1

High Clock Period

t

HIGH

4.7

µsec

Note 1

SCLK and SDA Rise Time

t

R

1000

nsec

Note 1

SCLK and SDA Fall Time

t

F

300

nsec

Note 1

Start Condition Setup Time

t

SU(START)

4.7

µsec

Note 1

SCLK Clock Period Time

t

SC

10

µsec

Note 1

Start Condition Hold Time

t

H(START)

4.0

µsec

Note 1

Data in SetupTime to SCLK 
High

t

SU-DATA

250

nsec

Note 1

Data in Hold Time after SCLK 
Low

t

H-DATA

300

nsec

Note 1

Stop Condition Setup Time

t

SU(STOP)

4.0

µsec

Note 1

Bus Free Time Prior to New 
Transition

t

IDLE

4.7

µsec

Note 1

 and 

Note 2

Note 1: Not production tested, ensured by design, tested during characterization.

2: Time the bus must be free before a new transmission can start.

ELECTRICAL SPECIFICATIONS (CONTINUED)

Electrical Characteristics: Unless otherwise noted, all limits are specified for V

DD

 = 3.0V to 5.5V,

 -40°C <T

< +85°C.

Parameters

Sym.

Min.

Typ.

Max.

Units

Conditions

Note 1: Not production tested, ensured by design, tested during characterization.

2: For 5.0V > V

DD 

 5.5V, the limit for V

IH

 = 2.2V.

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DS20001734C-page 5

TC654/TC655

FIGURE 1-1:

Bus Timing Data.

t

SU(START)

t

H(START)

t

SU-DATA

t

SU(STOP)

t

IDLE

A = Start Condition 
B = MSB of Address Clocked into Slave 
C = LSB of Address Clocked into Slave 
D = R/W Bit Clocked into Slave 
E = Slave Pulls SDA Line Low

A

B

C

D

E

F

G

H

I

J

K

L

M

F = Acknowledge Bit Clocked into Master 
G = MSB of Data Clocked into Slave 
H = LSB of Data Clocked into Slave 
I = Slave Pulls SDA Line Low

J = Acknowledge Clocked into Master 
K = Acknowledge Clock Pulse 
L = Stop Condition, Data Executed by Slave 
M = New Start Condition

t

LOW

t

HIGH

SCLK

SDA

t

H-DATA

SMBus Write Timing Diagram

t

SU(START)

t

H(START)

t

SU-DATA

t

SU(STOP)

t

IDLE

A = Start Condition 

B = MSB of Address Clocked into Slave 

C = LSB of Address Clocked into Slave 

D = R/W Bit Clocked into Slave 

A

B

C

D

E F

G

H

I

J

K

E = Slave Pulls SDA Line Low 

F = Acknowledge Bit Clocked into Master 

G = MSB of Data Clocked into Master 

H = LSB of Data Clocked into Master 

t

LOW

t

HIGH

I = Acknowledge Clock Pulse 

J = Stop Condition 

K = New Start Condition

SCLK

SDA

SMBus Read Timing Diagram

E

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TC654/TC655

DS20001734C-page 6

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2.0

TYPICAL PERFORMANCE CURVES

FIGURE 2-1:

I

DD

 vs. Temperature.

FIGURE 2-2:

I

DD

 Shutdown vs. 

Temperature.

FIGURE 2-3:

PWM, Source Current vs. 

Temperature.

FIGURE 2-4:

PWM, Sink Current vs. 

Temperature.

FIGURE 2-5:

Fault V

OL

 vs. Temperature.

FIGURE 2-6:

PWM Frequency vs. 

Temperature.

Note:

The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore outside the warranted range.

130

135

140

145

150

155

160

165

170

175

180

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (°C)

I

DD

 (µA

)

V

DD

 = 5.5 V

V

DD

 = 3.0 V

Pins 7,8, and 9 Open

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

9.000

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

S

hutdow

n I

DD

 (µA

)

V

DD

 = 3.0 V

V

DD

 = 5.5 V

5

10

15

20

25

30

35

-40

-25

-10

5

20

35

50

65

80

95

110

125

Temperature (°C)

S

our

ce C

u

rr

e

nt (m

A

)

V

DD

 = 5.5 V

V

DD

 = 5.0 V

V

DD

 = 4.0 V

V

DD

 = 3.0 V

V

OH

 = 0.8V

DD

2

4

6

8

10

12

14

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (°C)

S

ink C

u

rr

e

nt (m

A

)

V

DD

 = 5.5 V

V

DD

 = 5.0 V

V

DD

 = 4.0 V

V

DD

 = 3.0 V

V

OL

 = 0.1 V

DD

15

20

25

30

35

40

45

50

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

Faul

t V

OL

 (m

V

)

I

OL

 = 2.5 mA

V

DD

 = 5.5 V

V

DD

 = 5.0 V

V

DD

 = 4.0 V

V

DD

 = 3.0 V

27

28

29

30

31

32

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

P

W

M Fr

equency (H

z

)

V

DD

 = 5.5 V

V

DD

 = 3.0 V

C

F

 = 1.0 µF

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DS20001734C-page 7

TC654/TC655

FIGURE 2-7:

SDA I

OL

 vs. Temperature.

FIGURE 2-8:

V

CMAX

 vs. Temperature.

FIGURE 2-9:

V

CMIN

 vs. Temperature.

FIGURE 2-10:

RPM %error vs. 

Temperature.

FIGURE 2-11:

Sense Threshold 

(V

THSENSE

) Hysteresis vs. Temperature.

FIGURE 2-12:

SDA, SCLK Hysteresis vs. 

Temperature.

20

25

30

35

40

45

50

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

SDA I

OL

 (m

A

)

V

OL

 = 0.4 V

V

DD

 = 5.5 V

V

DD

 = 5.0 V

V

DD

 = 4.0 V

V

DD

 = 3.0 V

2.575

2.580

2.585

2.590

2.595

2.600

2.605

2.610

2.615

2.620

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

V

CM

a

x

 (V

)

V

DD

 = 3.0 V

V

DD

 = 4.0 V

V

DD

 = 5.0 V

V

DD

 = 5.5 V

1.180

1.185

1.190

1.195

1.200

1.205

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

V

CM

IN

 (V

)

V

DD

 = 3.0 V

V

DD

 = 5.0 V

V

DD

 = 5.5 V

V

DD

 = 4.0 V

0

1

2

3

4

5

6

7

8

9

10

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

R

P

M

 Erro

r (

%

)

V

DD

 = 3.0 V

V

DD

 = 5.5 V

V

DD

 = 5.0 V

C

F

 = 1.0 µF

20

25

30

35

40

45

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

V

THSENSE

 H

yster

esis (m

V

)

V

DD

 = 3.0V

V

DD

 = 5.5V

80

90

100

110

120

130

140

150

-40

-25

-10

5

20

35

50

65

80

95

110 125

Temperature (ºC)

S

D

A

 &

 S

C

LK

 H

yster

esis (m

V

)

V

DD

 = 3.0 V

V

DD

 = 5.0 V

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TC654/TC655

DS20001734C-page 8

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3.0

PIN FUNCTIONS

The descriptions of the pins are listed in 

Table 3-1

.

TABLE 3-1:

PIN FUNCTION TABLE

3.1

Analog Input (V

IN

)

A voltage range of 1.62V to 2.6V (typical) on this pin
drives an active duty-cycle of 30% to 100% on the
V

OUT

 pin.

3.2

Analog Output (C

F

)

Positive terminal for the PWM ramp generator timing
capacitor. The recommended C

F

 is 1 µF for 30 Hz

PWM operation.

3.3

SMBus Serial Clock Input (SCLK)

Clocks data into and out of the TC654/TC655. See

Section 5.0 “Serial Communication”

 for more infor-

mation on the serial interface.

3.4

Serial Data (Bi-directional) (SDA)

Serial data is transferred on the SMBus in both direc-
tions using this pin. See 

Section 5.0 “Serial Commu-

nication”

 for more information on the serial interface.

3.5

Digital (Open Drain) Output 
(FAULT)

When the fan’s RPM falls below the user-set RPM
threshold (or OTF occurs with TC655), a logic low sig-
nal is asserted.

3.6

Analog Input (SENSE2)

Fan current pulses are detected at this pin. These
pulses are counted and used in the calculation of the
Fan 2 RPM.

3.7

Analog Input (SENSE1)

Fan current pulses are detected at this pin. These
pulses are counted and used in the calculation of the
Fan 1 RPM.

3.8

Digital Output (V

OUT

)

This active high complimentary output drives the base
of an external transistor or the gate of a MOSFET.

3.9

Power Supply Input (V

DD

)

The V

DD

 pin with respect to GND provides power to the

device. This bias supply voltage may be independent of
the fan power supply.

Name

Function

V

IN

Analog Input

C

F

Analog Output

SCLK

Serial Clock Input

SDA

Serial Data In/Out (Open Drain)

GND

Ground

FAULT

Digital (Open Drain) Output

SENSE2

Analog Input

SENSE1

Analog Input

V

OUT

Digital Output

V

DD

Power Supply Input

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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 V

IN

 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 V

IN

 voltage exceeds 2.6V (typi-

cal), both devices will set OTF (bit 5<X>) in the Status
Register to a '1'. The TC655 will additionally pull the
FAULT output low during an over-temperature condi-
tion.

FIGURE 4-1:

Typical Application Circuit.

1

2

3

4

5

6

7

8

9

10

V

IN

C

F

SCLK

SDA

GND

FAULT

SENSE2

SENSE1

V

OUT

V

DD

+5V

FAN

FAN

R

ISO1

R

ISO2

R

SENSE2

R

SENSE1

C

SENSE2

C

SENSE1

1

2

NTC Thermistor

R

1

R

2

C

1

0.01 µF

C

2

1 µF

100 k

 @ 25°C

PIC

®

Microcontroller

+12V

+5V

+5V

+5V

+5V

34.8 k

14.7 k

C

F

1.0 µF

R

SCLK

20 k

R

SDA

20 k

715

0.1 µF

0.1 µF

715

R

FAULT

20 k

Note: Refer to 

Table 7-1

 for R

SENSE1

 and R

SENSE2

 values.

TC654/TC655

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TC654/TC655

DS20001734C-page 10

 2002-2014 Microchip Technology Inc.

4.1

Fan Speed Control Methods

The speed of a DC brushless fan is proportional to the
voltage across it. For example, if a fan’s rating is
5000 RPM at 12V, it’s speed would be 2500 RPM at 6V.
This, of course, will not be exact, but should be close.

There are two main methods for fan speed control. The
first is pulse width modulation (PWM) and the second
is linear. Using either method the total system power
requirement to run the fan is equal. The difference
between the two methods is where the power is
consumed. 

The following example compares the two methods for
a 12V, 120 mA fan running at 50% speed. With 6V
applied across the fan, the fan draws an average cur-
rent of 68 mA. Using a linear control method, there are
6V across the fan and 6V across the drive element.
With 6V and 68 mA, the drive element is dissipating
410 mW of power. Using the PWM approach, the fan is
modulated at a 50% duty cycle, with most of the 12V
being dropped across the fan. With 50% duty cycle, the
fan draws an RMS current of 110 mA and an average
current of 72 mA. Using a MOSFET with a 1

 RDS

(on)

(a fairly typical value for this low current) the power dis-
sipation in the drive element would be: 12 mW (Irms

2

 *

RDS

(on)

). Using a standard 2N2222A NPN transistor

(assuming a Vce-sat of 0.8V), the power dissipation
would be 58 mW (Iavg* Vce-sat).

The PWM approach to fan speed control causes much
less power dissipation in the drive element. This allows
smaller devices to be used and will not require any spe-
cial heatsinking to get rid of the power being dissipated
in the package.

The other advantage to the PWM approach is that the
voltage being applied to the fan is always near 12V.
This eliminates any concern about not supplying a high
enough voltage to run the internal fan components,
which is very relevant in linear fan speed control.

4.2

PWM Fan Speed Control

The TC654 and TC655 devices implement PWM fan
speed control by varying the duty cycle of a fixed fre-
quency pulse train. The duty cycle of a waveform is the
on time divided by the total period of the pulse. For
example, given a 100 Hz waveform (10 msec.) with an
on time of 5.0 msec, the duty cycle of this waveform is
50% (5.0 msec/10.0 msec). An example of this is
illustrated in 

Figure 4-2

.

FIGURE 4-2:

Duty Cycle Of A PWM 

Waveform.

The TC654 and TC655 generate a pulse train with a
typical frequency of 30 Hz (C

F

 = 1 µF). The duty cycle

can be varied from 30% to 100%. The pulse train gen-
erated by the TC654/TC655 devices drives the gate of
an external N-channel MOSFET or the base of an NPN
transistor (

Figure 4-3

). See 

Section 7.5 “Output Drive

Device Selection”

 for more information on output

drive device selection.

FIGURE 4-3:

PWM Fan Drive.

By modulating the voltage applied to the gate of the
MOSFET Qdrive, the voltage applied to the fan is also
modulated. When the V

OUT

 pulse is high, the gate of

the MOSFET is turned on, pulling the voltage at the
drain of Qdrive to 0V. This places the full 12V across
the fan for the Ton period of the pulse. When the duty
cycle of the drive pulse is 100% (full on, Ton = T), the
fan will run at full speed. As the duty cycle is decreased
(pulse on time “Ton” is lowered), the fan will slow down
proportionally. With the TC654 and TC655 devices, the
duty cycle can be controlled through the analog input
pin (V

IN

) or through the SMBus interface by using the

Duty-Cycle Register. See 

Section 4.5 “Duty Cycle

Control (V

IN

 and Duty-Cycle Register)”

 for more

details on duty cycle control.

T

Ton

Toff

T = Period
T = 1/F
F = Frequency

D = Duty Cycle
D = Ton / T

TC654/

TC655

FAN

12V

Qdrive

V

DD

GND

V

OUT

G

D

S

Maker
Microchip Technology Inc.
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