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PDF TC649 Data sheet ( Hoja de datos )
| Número de pieza | TC649 | |
| Descripción | PWM Fan Speed Controller | |
| Fabricantes | Microchip | |
| Logotipo |  |
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M
TC649
PWM Fan Speed Controller with Auto-Shutdown
and FanSense™ Technology
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 TC649
Supply Voltage
- Supports any Fan Voltage
• FanSense™ Fault Detection Circuits Protect
Against Fan Failure and Aid System Testing
• Automatic Shutdown Mode for “Green” Systems
• Supports Low Cost NTC/PTC Thermistors
• Space Saving 8-Pin MSOP Package
Applications
• Power Supplies
• Computers
• File Servers
• Portable Computers
• 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 2
VAS 3
GND 4
TC649
8 VDD
7 VOUT
6 FAULT
5 SENSE
General Description
The TC649 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 VIN input fur-
nishes the required control voltage of 1.25V to 2.65V
(typical) for 0% to 100% PWM duty cycle. The TC649
automatically suspends fan operation when measured
temperature (VIN) is below a user programmed
minimum setting (VAS). 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.
In normal fan operation, a pulse train is present at
SENSE (Pin 5). The TC649 features Microchip
Technology’s proprietary FanSenseTM technology for
increasing system reliability. A missing pulse detector
monitors this pin during fan operation. A stalled, open
or unconnected fan causes the TC649 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. See Section 5.0, “Typical Applications”,
for more information and system design guidelines.
The TC649 is available in the 8-pin PDIP, SOIC and
MSOP packages and is available in the industrial and
extended commercial temperature ranges.
2002 Microchip Technology Inc.
DS21449C-page 1
1 page  
3.0 DETAILED DESCRIPTION
3.1 PWM
The PWM circuit consists of a ramp generator and
threshold detector. The frequency of the PWM is
determined by the value of the capacitor connected to
the CF input. A frequency of 30 Hz is recommended for
most applications (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 the datasheet. This output has
asymmetric complementary 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 or auto-
shutdown mode. If the PWM frequency is 30 Hz (CF =
1 µF) the resulting start-up time will be approximately
one second. If a fan fault is detected (see Section 3.5,
FAULT Output), the Diagnostic Timer is triggered once,
followed by the Start-up Timer. If the fault persists, the
device is shut down (see Section 3.5, FAULT Output).
3.4 SENSE Input
(FanSense™ Technology)
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 or auto-shutdown mode, and pulses are not
appearing at the SENSE input, a fault exists.
The short, rapid change in fan current (high dl/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.
TC649
3.5 FAULT Output
Pulses appearing at SENSE due to the PWM turning
on are blanked, and the remaining pulses are filtered
by a missing pulse detector. If consecutive pulses are
not detected for thirty-two 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 tran-
sient 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. The TC649 is thus prevented from
attempting to drive a fan under catastrophic fault
conditions.
One of two things will restore operation: Cycling power
off and then on again; or pulling VIN below VSHDN and
releasing it to a level above VREL. When one of these
two conditions is satisfied, the normal start-up cycle is
triggered and operation will resume, provided the fault
has been cleared.
3.6 Auto-Shutdown Mode
If the voltage on VIN becomes less than the voltage on
VAS, the fan is automatically shut off (auto-shutdown
mode). The TC649 exits auto-shutdown mode when
the voltage on VIN becomes higher than the voltage on
VAS by VHAS (the auto-shutdown hysteresis voltage,
see Figure 3-1). The Start-up Timer is triggered and
normal operation is resumed upon exiting auto-shut-
down mode. The FAULT output is unconditionally
inactive in auto-shutdown mode.
2002 Microchip Technology Inc.
DS21449C-page 5
5 Page 
VDD
R1 IIN
IDIV
VAS
R2
GND
FIGURE 5-3:
VAS Circuit.
Per Section 1.0, “Electrical Characteristics”, the leak-
age current at the VAS pin is no more than 1 µA. It is
conservative to design for a divider current, IDIV, of
100 µA. If VDD = 5.0V then:
EQUATION
IDIV = 1e– 4A
R1 + R2 =
5.0V
R1 + R2 , therefore
5.0V
1e–4A
= 50,000Ω = 50 kΩ
We can further specify R1 and R2 by the condition that
the divider voltage is equal to our desired VAS. This
yields the following:
EQUATION
VAS =
VDD x R2
R1 + R2
Solving for the relationship between R1 and R2 results
in:
EQUATION
R1 = R2 x
VDD - VAS
VAS
= R2 x
5 -1.53
1.53
In the case of this example, R1 = (2.27) R2. Substituting
this relationship back into the VAS equation above
yields the resistor values:
R2 = 15.3 kΩ, and
R1 = 34.7 kΩ
In this case, the standard values of 34.8 kΩ and
15.4 kΩ are very close to the calculated values and
would be more than adequate.
TC649
5.3 Operations at Low Duty Cycle
One boundary condition which may impact the
selection of the minimum fan speed is the irregular
activation of the Diagnostic Timer due to the TC649
“missing” fan commutation pulses at low speeds. This
is a natural consequence of low PWM duty cycles (typ-
ically 25% or less). Recall that the SENSE function
detects commutation of the fan as disturbances in the
current through RSENSE. These can only occur when
the fan is energized (i.e., VOUT is “on”). At very low duty
cycles, the 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 TC649 may fail
to capture a pulse within the 32-cycle missing pulse
detector window. If 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 accelerates briefly when the Diagnostic
Timer fires. For this reason, it is recommended that VAS
be set no lower than 1.8V.
5.4 FanSense™ Network
(RSENSE and CSENSE)
The FanSense network, comprised of RSENSE and
CSENSE, allows the TC649 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 nec-
essary amount of gain (i.e., the current-to-voltage con-
version ratio). A 0.1 µF ceramic capacitor is
recommended for CSENSE. Smaller values require
larger sense resistors, and higher value capacitors are
bulkier and more expensive. Using a 0.1 µF capacitor
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 net-
work.
2002 Microchip Technology Inc.
DS21449C-page 11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet TC649.PDF ] | |
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