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PDF TC642B Data sheet ( Hoja de datos )
| Número de pieza | TC642B | |
| Descripción | PWM Fan Speed Controllers | |
| Fabricantes | Microchip | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de TC642B (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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M TC642B/TC647B
PWM Fan Speed Controllers With Minimum Fan Speed,
Fan Restart and FanSense™ Technology for Fault Detection
Features
• Temperature-Proportional Fan Speed for Acoustic
Noise Reduction and Longer Fan Life
• Efficient PWM Fan Drive
• 3.0V to 5.5V Supply Range:
- Fan Voltage Independent of TC642B/TC647B
Supply Voltage
- Supports any Fan Voltage
• FanSense™ Fault Detection Circuit Protects
Against Fan Failure and Aids System Testing
• Shutdown Mode for "Green" Systems
• Supports Low Cost NTC/PTC Thermistors
• Over-Temperature Indication (TC642B only)
• Fan Auto-Restart
• Space-Saving 8-Pin MSOP Package
Applications
• Personal Computers & Servers
• LCD Projectors
• Datacom & Telecom Equipment
• Fan Trays
• File Servers
• General Purpose Fan Speed Control
Package Types
MSOP, PDIP, SOIC
VIN
CF
VMIN
GND
1
2
3
4
TC642B
TC647B
8 VDD
7 VOUT
6 FAULT
5 SENSE
Description
The TC642B/TC647B devices are new versions of the
existing TC642/TC647 fan speed controllers. These
devices are switch mode, fan speed controllers that
incorporate a new fan auto-restart function. Tempera-
ture-proportional speed control is accomplished using
pulse width modulation. A thermistor (or other voltage
output temperature sensor) connected to the VIN input
supplies the required control voltage of 1.20V to 2.60V
(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 TC642B and TC647B also feature Microchip
Technology's proprietary 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 TC642B/
TC647B device to turn the VOUT output on full (100%
duty cycle). If the fault persists (a fan current pulse is
not detected within a 32/f period), the FAULT output
goes low. Even with the FAULT output low, the VOUT
output is on full during the fan fault condition in order to
attempt to restart the fan. FAULT is also asserted if the
PWM reaches 100% duty cycle (TC642B only), indicat-
ing that maximum cooling capability has been reached
and a possible overheating condition exists.
The TC642B and TC647B devices are available in 8-pin
plastic MSOP, SOIC and PDIP packages. The specified
temperature range of these devices is -40 to +85ºC.
2003 Microchip Technology Inc.
DS21756B-page 1
1 page  
TIMING SPECIFICATIONS
VOUT
tSTARTUP
FAULT
TC642B/TC647B
SENSE
FIGURE 1-1:
TC642B/TC647B Start-Up Timing.
VOUT
33.3 msec (CF = 1 µF)
tMP
tDIAG
tMP
FAULT
SENSE
FIGURE 1-2:
VOUT
Fan Fault Occurrence.
tMP
FAULT
SENSE
FIGURE 1-3:
Minimum 16 pulses
Recovery From Fan Fault.
2003 Microchip Technology Inc.
DS21756B-page 5
5 Page 
4.0 DEVICE OPERATION
The TC642B/TC647B devices are a family of tempera-
ture proportional, PWM mode, fan speed controllers.
Features of the family include minimum fan speed, fan
auto-shutdown mode, fan auto-restart, remote shut-
down, over-temperature indication and fan fault
detection.
The TC642B/TC647B family is slightly different from
the original TC64X family, which includes the TC642,
TC646, TC647, TC648 and TC649 devices. Changes
have been made to adjust the operation of the device
during a fan fault condition.
The key change to the TC64XB family of devices
(TC642B, TC647B, TC646B, TC648B, TC649B) is that
the FAULT and VOUT outputs no longer “latch” to a
state during a fan fault condition. The TC64XB family
will continue to monitor the operation of the fan so that
when the fan returns to normal operation, the fan speed
controller will also return to normal operation (PWM
mode). The operation and features of these devices
are discussed in the following sections.
4.1 Fan Speed Control Methods
The speed of a DC brushless fan is proportional to the
voltage across it. This relationship will vary from fan to
fan and should be characterized on an individual basis.
The speed versus applied voltage relationship can then
be used to set up the fan speed control algorithm.
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
current of 68 mA.
Using a linear control method, there is 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 voltage 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 ΩRDS(on) (a fairly
typical value for this low current), the power dissipation
in the drive element would be: 12 mW (Irms2 * 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 results in
much less power dissipation in the drive element,
allowing smaller devices to be used while not requiring
TC642B/TC647B
special heatsinking to remove the power being
dissipated in the package.
The other advantage of 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 TC642B and TC647B 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, a 100 Hz waveform (10 ms) with an on time
of 5.0 ms has a duty cycle of 50% (5.0 ms / 10.0 ms).
This example is illustrated in Figure 4-1.
t
ton toff
D = Duty Cycle
D = ton / t
t = Period
t = 1/f
f = Frequency
FIGURE 4-1:
Waveform.
Duty Cycle of a PWM
The TC642B and TC647B generate a pulse train with a
typical frequency of 30 Hz (CF = 1 µF). The duty cycle
can be varied from 0% to 100%. The pulse train gener-
ated by the TC642B/TC647B device drives the gate of
an external N-channel MOSFET or the base of an NPN
transistor (shown in Figure 4-2). See Section 5.5, “Out-
put Drive Device Selection”, for more information.
12V
VDD
TC642B VOUT
TC647B
GND
FAN
D
G QDRIVE
S
FIGURE 4-2:
PWM Fan Drive.
2003 Microchip Technology Inc.
DS21756B-page 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet TC642B.PDF ] | |
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