PWM Fan Speed Controller with Auto-Shutdown and FanSense Technology
2002 Microchip Technology Inc.
DS21446C-page 1
M
TC646
Features
Temperature Proportional Fan Speed for Acoustic
Control and Longer Fan Life
Efficient PWM Fan Drive
3.0V to 5.5V Supply Range:
- Fan Voltage Independent of TC646
Supply Voltage
- Supports any Fan Voltage
FanSenseTM
Fault Detection Circuits Protect
Against Fan Failure and Aid System Testing
Shutdown Mode for "Green" Systems
Supports Low Cost NTC/PTC Thermistors
Space Saving 8-Pin MSOP Package
Over-temperature Indication
Applications
Power Supplies
Computers
File Servers
Portable Computers
Telecom Equipment
UPS, Power Amps
General Purpose Fan Speed Control
Available Tools
Fan Controller Demonstration Board (TC642DEMO)
Fan Controller Evaluation Kit (TC642EV)
Package Types
General Description
The TC646 is a switch mode, fan speed controller for
use with brushless DC fans. Temperature proportional
speed control is accomplished using pulse width mod-
ulation (PWM). A thermistor (or other voltage output
temperature sensor) connected to the V
IN
input fur-
nishes the required control voltage of 1.25V to 2.65V
(typical) for 0% to 100% PWM duty cycle. The TC646
automatically suspends fan operation when measured
temperature (V
IN
) is below a user programmed
minimum setting (V
AS
). An integrated Start-up Timer
ensures reliable motor start-up at turn-on, coming out
of shutdown mode, auto-shutdown mode or following a
transient fault.
The TC646 features Microchip Technology's propri-
etary FanSenseTM technology for increasing system
reliability. In normal fan operation, a pulse train is
present at SENSE (Pin 5). A missing-pulse detector
monitors this pin during fan operation. A stalled, open,
or unconnected fan causes the TC646 to trigger its
Start-up Timer once. If the fault persists, the FAULT
output goes low and the device is latched in its shut-
down mode. FAULT is also asserted if the PWM
reaches 100% duty cycle, indicating a possible thermal
runaway situation, although the fan continues to run.
See Section 5.0, "Typical Applications", for more
information and system design guidelines.
The TC646 is available in the 8-pin plastic DIP, SOIC
and MSOP packages and is available in the industrial
and extended commercial temperature ranges.
1
8
2
7
3
6
4
5
TC646
GND
C
F
V
IN
V
AS
FAULT
SENSE
V
DD
V
OUT
SOIC/PDIP/MSOP
PWM Fan Speed Controller with Auto-Shutdown
and FanSense
TM
Technology
TC646
DS21446C-page 2
2002 Microchip Technology Inc.
Functional Block Diagram
FAULT
SHDN
SENSE
PWM
OTF
GND
70mV (typ.)
10k
V
AS
V
SHDN
V
IN
C
F
V
DD
V
OUT
TC646
Control
Logic
+
V
OTF
+
+
+
+
3 x T
PWM
Timer
Start-up
Timer
Clock
Generator
Missing
Pulse
Detect.
2002 Microchip Technology Inc.
DS21446C-page 3
TC646
1.0
ELECTRICAL
CHARACTERISTICS
Absolute Maximum Ratings*
Supply Voltage ......................................................... 6V
Input Voltage, Any Pin..... (GND 0.3V) to (V
DD
+0.3V)
Package Thermal Resistance:
PDIP (R
JA
)............................................. 125C/W
SOIC (R
JA
) ............................................155C/W
MSOP (R
JA
) .......................................... 200C/W
Specified Temperature Range ........... -40C to +125C
Storage Temperature Range.............. -65C to +150C
*Stresses above those listed under "Absolute Maximum Rat-
ings" may cause permanent damage to the device. These are
stress ratings only and functional operation of the device at
these or any other conditions above those indicated in the
operation sections of the specifications is not implied. Expo-
sure to absolute maximum rating conditions for extended peri-
ods may affect device reliability.
DC ELECTRICAL SPECIFICATIONS
Electrical Characteristics: Unless otherwise specified, T
MIN
T
A
T
MAX
, V
DD
= 3.0V to 5.5V
Symbol
Parameter
Min
Typ
Max
Units
Test Conditions
V
DD
Supply Voltage
3.0
--
5.5
V
I
DD
Supply Current, Operating
--
0.5
1.0
mA
Pins 6, 7 Open,
C
F
= 1 F, V
IN
= V
C(MAX)
I
DD(SHDN)
Supply Current, Shutdown/
Auto-shutdown Mode
--
25
--
A
Pins 6, 7 Open;
Note 1
C
F
=1 F, V
IN
= 0.35V
I
IN
V
IN
,
V
AS
Input Leakage
-1.0
--
+1.0
A
Note 1
V
OUT
Output
t
R
V
OUT
Rise Time
--
--
50
sec I
OH
= 5 mA, Note 1
t
F
V
OUT
Fall Time
--
--
50
sec I
OL
= 1 mA, Note 1
t
SHDN
Pulse Width(On V
IN
) to Clear
Fault Mode
30
--
--
sec V
SHDN
, V
HYST
Specifications,
Note 1
I
OL
Sink Current at V
OUT
Output
1.0
--
--
mA
V
OL
= 10% of V
DD
I
OH
Source Current at V
OUT
Output
5.0
--
--
mA
V
OH
= 80% of V
DD
SENSE Input
V
TH(SENSE)
SENSE Input Threshold
Voltage with Respect to GND
50
70
90
mV
Note 1
FAULT Output
V
OL
Output Low Voltage
--
--
0.3
V
I
OL
= 2.5 mA
t
MP
Missing Pulse Detector Timer
--
32/F
--
Sec
C
F
= 1.0 F
t
STARTUP
Start-up Timer
--
32/F
--
Sec
C
F
= 1.0 F
t
DIAG
Diagnostic Timer
--
3/F
--
Sec
C
F
= 1.0 F
Note 1:
Ensured by design, not tested.
TC646
DS21446C-page 4
2002 Microchip Technology Inc.
V
IN
, V
AS
Inputs
V
C(MAX),
V
OTF
Voltage at V
IN
for 100% Duty
Cycle and Overtemp. Fault
2.5
2.65
2.8
V
V
C(SPAN)
V
C(MAX)
- V
C(MIN)
1.3
1.4
1.5
V
V
AS
Auto-shutdown Threshold
V
C(MAX) ~
V
C(SPAN)
--
V
C(MAX)
V
V
SHDN
Voltage Applied to V
IN
to
ensure Reset/Shutdown
--
--
V
DD
x 0.13
V
V
REL
Voltage Applied to V
IN
to
Release Reset Mode
V
DD
x 0.19
--
--
V
V
DD
= 5V,
See Figure 5-11
V
HYST
Hysteresis on V
SHDN,
V
REL
--
0.01 x V
DD
--
V
V
HAS
Hysteresis on Auto-shutdown
Comparator
--
70
--
mV
Pulse Width Modulator
F
OSC
PWM Frequency
26
30
34
Hz
C
F
= 1.0 F
DC ELECTRICAL SPECIFICATIONS (CONTINUED)
Electrical Characteristics: Unless otherwise specified, T
MIN
T
A
T
MAX
, V
DD
= 3.0V to 5.5V
Symbol
Parameter
Min
Typ
Max
Units
Test Conditions
Note 1:
Ensured by design, not tested.
2002 Microchip Technology Inc.
DS21446C-page 5
TC646
2.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1:
PIN FUNCTION TABLE
2.1
Analog Input (V
IN
)
The thermistor network (or other temperature sensor)
connects to the V
IN
input. A voltage range of 1.25V to
2.65V (typical) on this pin drives an active duty cycle of
0% to 100% on the V
OUT
pin. The TC646 enters shut-
down mode when V
IN
V
SHDN
.
During shutdown, the
FAULT output is inactive, and supply current falls to
25 A (typical). The TC646 exits shutdown mode
when V
IN
V
REL
(see Section 5.0, "Typical
Applications", for details).
2.2
Analog Output (C
F
)
C
F
is the positive terminal for the PWM ramp generator
timing capacitor. The recommended C
F
is 1 F for
30 Hz PWM operation.
2.3
Analog Input (V
AS
)
An external resistor divider connected to the V
AS
input
sets the auto-shutdown threshold. Auto-shutdown
occurs when V
IN
V
AS
. The fan is automatically
restarted when V
IN
(V
AS
+ V
HAS
) (see Section 5.0,
"Typical Applications", for more details).
2.4
Ground (GND)
GND denotes the ground terminal.
2.5
Analog Input (SENSE)
Pulses are detected at the SENSE pin as fan rotation
chops the current through a sense resistor (R
SENSE
).
The absence of pulses indicates a fault (see
Section 5.0, "Typical Applications", for more details).
2.6
Digital Output (FAULT)
The FAULT line goes low to indicate a fault condition.
When FAULT goes low due to a fan fault condition, the
device is latched in shutdown mode until deliberately
cleared or until power is cycled. FAULT will also be
asserted when the PWM reaches 100% duty cycle,
indicating that maximum cooling capability has been
reached and a possible over-temperature condition
may occur. This is a non-latching state and the FAULT
output will go high when the PWM duty cycle goes
below 100%.
2.7
Digital Output (V
OUT
)
V
OUT
is an active high complimentary output that drives
the base of an external NPN transistor (via an appropri-
ate base resistor) or the gate of an N-channel MOS-
FET. This output has asymmetrical drive (see
Section 1.0, "Electrical Characteristics").
2.8
Power Supply Input (V
DD
)
V
DD
may be independent of the fan's power supply
(see Section 1.0, "Electrical Characteristics").
Pin No.
Symbol
Description
1
V
IN
Analog Input
2
C
F
Analog Output
3
V
AS
Analog Input
4
GND
Ground Terminal
5
SENSE
Analog Input
6
FAULT
Digital (Open Collector) Output
7
V
OUT
Digital Output
8
V
DD
Power Supply Input
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