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PDF TC647 Data sheet ( Hoja de datos )

Número de pieza TC647
Descripción PWM Fan Speed Controller
Fabricantes Microchip 
Logotipo Microchip Logotipo



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M
TC647
PWM Fan Speed Controller with FanSenseTechnology
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 TC647
Supply Voltage
- Supports any Fan Voltage
• FanSense™ Technology 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
Applications
• Power Supplies
• Personal Computers
• File Servers
• Telecom Equipment
• UPSs, Power Amps
• General Purpose Fan Speed Control
Available Tools
• Fan Controller Demonstration Board (TC642DEMO)
• Fan Controller Evaluation Kit (TC642EV)
Package Types
SOIC/PDIP/MSOP
VIN 1
CF
VMIN
2
3
GND 4
TC647
8 VDD
7 VOUT
6 FAULT
5 SENSE
General Description
The TC647 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 VIN furnishes the
required control voltage of 1.25V to 2.65V (typical) for
0% to 100% PWM duty cycle. Minimum fan speed is
set by a simple resistor divider on the VMIN input. An
integrated Start-up Timer ensures reliable motor start-
up at turn-on, coming out of shutdown mode or
following a transient fault. A logic low applied to VMIN
(Pin 3) causes fan shutdown.
The TC647 also features Microchip Technology's pro-
prietary FanSense™ 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 TC647 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.
The TC647 is available in the 8-pin plastic DIP, SOIC
and MSOP packages and is available in the industrial
and extended commercial temperature ranges.
2002 Microchip Technology Inc.
DS21447C-page 1

1 page




TC647 pdf
3.0 DETAILED DESCRIPTION
3.1 PWM
The PWM circuit consists of a ramp generator and
threshold detector. The frequency of the PWM is deter-
mined by the value of the capacitor connected to the CF
input. A frequency of 30 Hz is recommended
(CF = 1 µF). The PWM is also the time base for the
Start-up Timer (see Section 3.3, “Start-Up Timer”). The
PWM voltage control range is 1.25V to 2.65V (typical)
for 0% to 100% output duty cycle.
3.2 VOUT Output
The VOUT pin is designed to drive a low cost transistor
or MOSFET as the low side power switching element in
the system. Various examples of driver circuits will be
shown throughout this data sheet. This output has an
asymmetric complimentary drive and is optimized for
driving NPN transistors or N-channel MOSFETs. Since
the system relies on PWM rather than linear control,
the power dissipation in the power switch is kept to a
minimum. Generally, very small devices (TO-92 or SOT
packages) will suffice.
3.3 Start-Up Timer
To ensure reliable fan start-up, the Start-up Timer turns
the VOUT output on for 32 cycles of the PWM whenever
the fan is started from the off state. This occurs at
power up and when coming out of shutdown mode. If
the PWM frequency is 30 Hz (CF = 1 µF), the resulting
start-up time will be approximately one second. If a
fault is detected, the Diagnostic Timer is triggered
once, followed by the Start-up Timer. If the fault
persists, the device is shut down (see Section 3.6,
“FAULT Output”).
3.4 Shutdown Control (Optional)
If VMIN (Pin 3) is pulled below VSHDN, the TC647 will go
into shutdown mode. This can be accomplished by
driving VMIN with an open-drain logic signal or using an
external transistor, as shown in Figure 3-1. All functions
are suspended until the voltage on VMIN becomes
higher than VREL (0.85V @ VDD = 5.0V). Pulling VMIN
below VSHDN will always result in complete device
shutdown and reset. The FAULT output is
unconditionally inactive in shutdown mode.
A small amount of hysteresis, typically one percent of
VDD (50 mV at VDD = 5.0V), is designed into the VSHDN/
VREL threshold. The levels specified for VSHDN and
VREL in Section 1.0, “Electrical Characteristics”,
include this hysteresis plus adequate margin to
account for normal variations in the absolute value of
the threshold and hysteresis.
TC647
CAUTION: Shutdown mode is unconditional. That is,
the fan will not be activated regardless of the voltage
at VIN. The fan should not be shut down until all heat
producing activity in the system is at a negligible
level.
3.5 SENSE Input
(FanSenseTechnology)
The SENSE input (Pin 5) is connected to a low value
current sensing resistor in the ground return leg of the
fan circuit. During normal fan operation, commutation
occurs as each pole of the fan is energized. This
causes brief interruptions in the fan current, seen as
pulses across the sense resistor. If the device is not in
shutdown mode, and pulses are not appearing at the
SENSE input, a fault exists.
The short, rapid change in fan current (high dI/dt)
causes a corresponding dV/dt across the sense
resistor, RSENSE. The waveform on RSENSE is
differentiated and converted to a logic-level, pulse-train
by CSENSE and the internal signal processing circuitry.
The presence and frequency of this pulse-train is a
direct indication of fan operation. See Section 5.0,
“Typical Applications”, for more details.
3.6 FAULT Output
Pulses appearing at SENSE due to the PWM turning
on are blanked with the remaining pulses being filtered
by a missing pulse detector. If consecutive pulses are
not detected for 32 PWM cycles (1 Sec if CF = 1 µF),
the Diagnostic Timer is activated and VOUT is driven
high continuously for three PWM cycles (100 msec if
CF = 1 µF). If a pulse is not detected within this window,
the Start-up Timer is triggered (see Section 3.3, “Start-
Up Timer”). This should clear a transient fault condition.
If the missing pulse detector times out again, the PWM
is stopped and FAULT goes low. When FAULT is
activated due to this condition, the device is latched in
shutdown mode and will remain off indefinitely.
Note:
At this point, action must be taken to restart
the fan by momentarily pulling VMIN below
VSHDN, or cycling system power. In either
case, the fan cannot remain disabled due
to a fault condition as severe system dam-
age could result. If the fan cannot be
restarted, the system should be shut down.
The TC647 may be configured to continuously attempt
fan restarts, if so desired.
2002 Microchip Technology Inc.
DS21447C-page 5

5 Page





TC647 arduino
VDD
R1 IIN
IDIV VMIN
R2
GND
FIGURE 5-3:
VMIN Circuit.
We can further specify R1 and R2 by the condition that
the divider voltage is equal to our desired VMIN. This
yields the following equation:
EQUATION
VMIN =
VDD x R2
R1 + R2
Solving for the relationship between R1 and R2 results
in the following equation:
EQUATION
R1 = R2 x
VDD - VMIN
VMIN
In this example, R1 = (1.762) R2. Substituting this rela-
tionship back into the previous equation yields the
resistor values:
R2 = 18.1 k
R1 = 31.9 k
In this case, the standard values of 31.6 kand
18.2 kare very close to the calculated values and
would be more than adequate.
5.3 Operations at Low Duty Cycle
One boundary condition which may impact the selec-
tion of the minimum fan speed is the irregular activation
of the Diagnostic Timer due to the TC647 “missing” fan
commutation pulses at low speeds. This is a natural
consequence of low PWM duty cycles (typically 25% or
less). Recall that the SENSE function detects commu-
tation of the fan as disturbances in the current through
RSENSE. These can only occur when the fan is ener-
gized (i.e., VOUT is “on”). At very low duty cycles, the
TC647
VOUT output is “off” most of the time. The fan may be
rotating normally, but the commutation events are
occurring during the PWM’s off-time.
The phase relationship between the fan’s commutation
and the PWM edges tends to “walk around” as the
system operates. At certain points, the TC647 may fail
to capture a pulse within the 32-cycle missing pulse
detector window. When this happens, the 3-cycle
Diagnostic Timer will be activated, the VOUT output will
be active continuously for three cycles and, if the fan is
operating normally, a pulse will be detected. If all is
well, the system will return to normal operation. There
is no harm in this behavior, but it may be audible to the
user as the fan will accelerate briefly when the
Diagnostic Timer fires. For this reason, it is
recommended that VMIN be set no lower than 1.8V.
5.4 FanSenseNetwork
(RSENSE and CSENSE)
The FanSense network, comprised of RSENSE and
CSENSE, allows the TC647 to detect commutation of
the fan motor (FanSense™ technology). This network
can be thought of as a differentiator and threshold
detector. The function of RSENSE is to convert the fan
current into a voltage. CSENSE serves to AC-couple this
voltage signal and provide a ground referenced input to
the SENSE pin. Designing a proper SENSE network is
simply a matter of scaling RSENSE to provide the
necessary amount of gain (i.e., the current-to-voltage
conversion ratio). A 0.1 µF ceramic capacitor is recom-
mended for CSENSE. Smaller values require larger
sense resistors, and higher value capacitors are bulkier
and more expensive. Using a 0.1 µF results in
reasonable values for RSENSE. Figure 5-4 illustrates a
typical SENSE network. Figure 5-5 shows the
waveforms observed using a typical SENSE network.
VDD
FAN
VOUT
SENSE
RBASE
CSENSE
(0.1 µF Typ.)
Q1
RSENSE
FIGURE 5-4:
GND
SENSE Network.
2002 Microchip Technology Inc.
DS21447C-page 11

11 Page







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