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PDF TC648 Data sheet ( Hoja de datos )
| Número de pieza | TC648 | |
| Descripción | Fan Speed Controller | |
| Fabricantes | Microchip | |
| Logotipo |  |
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M
TC648
Fan Speed Controller with Auto-Shutdown
and Over-Temperature Alert
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 TC648
Supply Voltage
- Supports any Fan Voltage
• Over-temperature Fault Detection
• Automatic Shutdown Mode for “Green” Systems
• Supports Low Cost NTC/PTC Thermistors
• Space Saving 8-Pin MSOP Package
Applications
• Power Supplies
• Computers
• 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
CF
VAS
GND
1
2
3
4
TC648
8 VDD
7 VOUT
6 OTF
5 NC
General Description
The TC648 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
furnishes the required control voltage of 1.25V to 2.65V
(typical) for 0% to 100% PWM duty cycle. The TC648
can be configured to operate in either auto-shutdown or
minimum speed mode. In auto-shutdown mode, fan
operation is automatically suspended when measured
temperature (VIN) is lower than a user programmed
minimum setting (VAS). The fan is automatically
restarted, and proportional speed control restored,
when VIN exceeds VAS (plus hysteresis). Operation in
minimum speed mode is similar to auto-shutdown
mode, with the exception that the fan is operated at a
user programmed minimum setting when the mea-
sured temperature is low. An integrated Start-up Timer
ensures reliable motor start-up at turn-on, and when
coming out of shutdown or auto-shutdown mode.
The over-temperature fault output (OTF) is asserted
when the PWM reaches 100% duty cycle, indicating a
possible thermal runaway situation.
The TC648 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.
DS21448C-page 1
1 page  
2.0 PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 2-1.
TABLE 2-1: PIN FUNCTION TABLE
Pin No. Symbol
Description
1 VIN Analog Input
2 CF Analog Output
3 VAS Analog Input
4 GND Ground Terminal
5 NC No Internal Connection
6 OTF Digital (Open Collector) Output
7 VOUT Digital Output
8 VDD Power Supply Input
2.1 Analog Input (VIN)
The thermistor network (or other temperature sensor)
connects to the VIN 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 VOUT pin (see Section 5.0, “Typical
Applications”, for more details).
2.2 Analog Output (CF)
CF is the positive terminal for the PWM ramp generator
timing capacitor. The recommended CF is 1 µF for
30 Hz PWM operation.
TC648
2.3 Analog Input (VAS)
An external resistor divider connected to the VAS input
sets the auto-shutdown threshold. Auto-shutdown
occurs when VIN ≤ VAS. During shutdown, supply
current falls to 25 µA (typical). The fan is automatically
restarted when VIN ≥ (VAS +VHAS) (see Section 5.0,
“Typical Applications” for more details).
2.4 Ground (GND)
GND denotes the ground Terminal.
2.5 No Connect
No internal connection.
2.6 Digital Output (OTF)
OTF goes low to indicate an over-temperature
condition. This occurs when the voltage at VIN > VOTF
(see Section 1.0, "Electrical Characteristics"). An over-
temperature indication is a non-latching condition.
2.7 Digital Output (VOUT)
VOUT 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 (VDD)
VDD may be independent of the fan’s power supply
(see Section 1.0, “Electrical Characteristics”).
2002 Microchip Technology Inc.
DS21448C-page 5
5 Page 
mistor resistance at TMIN. R2 is then calculated to
deliver the desired speed at TMIN. The values for R1, R2
and RT1 are then checked at TMAX for 2.65V nominal.
It may be necessary to adjust the values of R1 and R2
after the initial calculation to obtain the desired results.
The design equations are:
EQUATION
R1 = (0.1)(RT1MIN)
Where: RT1 = Thermistor resistance at TMIN
EQUATION
(RT1MIN)(R1)(VMIN)
R2 = (RT1MIN + R1)(VDD - VMIN)
Where VMIN = the value of VIN required for
minimum fan speed. VDD = Power Supply Voltage
EQUATION
VMAX =
(RT1MIN)(R1)(VMIN)
R2 (R1 + RT1MAX )(VDD)
Where RT1MAX = thermistor resistance at TMAX,
VMAX = the value of VIN required for maximum
fan speed.
Because the thermistor characteristics are fixed, it may
not be possible, in certain applications, to obtain the
desired values of VMIN and VMAX using the above
equations. In this case, the circuit in Figure 5-4 can be
used. Diode D1 clamps VIN to the voltage required to
sustain minimum speed. The calculations of R1 and
R2 for the temperature sensor are identical to the
equation on the previous page.
VDD
R3 RT1
D1
R4
R1
VIN
R2
FIGURE 5-4:
Minimum Fan Speed Circuit.
TC648
5.3 Auto-Shutdown Temperature
Design
A voltage divider on VAS sets the temperature at which
the part is automatically shut down if the sensed
temperature at VIN drops below the set temperature at
VAS (i.e. VIN < VAS).
As with the VIN input, 1.25V to 2.65V corresponds to
the temperature range of interest from T1 to T2,
respectively. Assuming that the temperature sensor
network designed previously is linearly related to
temperature, the shutdown temperature TAS is related
to T2 and T1 by:
EQUATION
2.65 - 1.25V = VAS - 1.25
T2 - T1
TAS - T1
( )VAS =
1.4V
T2 - T1
(TAS - T1) + 1.25
For example, if 1.25V and 2.65V at VIN corresponds to
a temperature range of T1 = 0°C to T2 = 125°C, and the
auto-shutdown temperature desired is 25°C, then the
VAS voltage is:
EQUATION
1.4V
VAS = (125 - 0) (25 - 0) + 1.25 = 1.53V
The VAS voltage may be set using a simple resistor
divider, as shown in Figure 5-5.
VDD
R1 IIN
IDIV VAS
R2
FIGURE 5-5:
GND
VAS Circuit.
2002 Microchip Technology Inc.
DS21448C-page 11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet TC648.PDF ] | |
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