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PDF TC646 Data sheet ( Hoja de datos )
| Número de pieza | TC646 | |
| Descripción | PWM Fan Speed Controller | |
| Fabricantes | Microchip | |
| Logotipo |  |
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M
TC646
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 TC646
Supply Voltage
- Supports any Fan Voltage
• FanSense™ 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
SOIC/PDIP/MSOP
VIN 1
CF
VAS
2
3
GND 4
TC646
8 VDD
7 VOUT
6 FAULT
5 SENSE
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 VIN 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 (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.
The TC646 features Microchip Technology's propri-
etary 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 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.
2002 Microchip Technology Inc.
DS21446C-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 SENSE Analog Input
6 FAULT 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. The TC646 enters shut-
down mode when VIN ≤ VSHDN. During shutdown, the
FAULT output is inactive, and supply current falls to
25 µA (typical). The TC646 exits shutdown mode
when VIN ≥ VREL (see Section 5.0, “Typical
Applications”, for 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.
TC646
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. 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 Analog Input (SENSE)
Pulses are detected at the SENSE pin as fan rotation
chops the current through a sense resistor (RSENSE).
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 (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.
DS21446C-page 5
5 Page 
5.1 Temperature Sensor Design
The temperature signal connected to VIN must output a
voltage in the range of 1.25V to 2.65V (typical) for 0%
to 100% of the temperature range of interest. The
circuit in Figure 5-2 illustrates a convenient way to
provide this signal.
VDD
IDIV
RT1
NTC Thermistor
100 kΩ@25˚C
R1 = 100 kΩ
VIN
R2 = 23.2kΩ
FIGURE 5-2:
Circuit.
Temperature Sensing
Figure 5-2 shows a simple temperature dependent
voltage divider circuit. RT1 is a conventional NTC ther-
mistor, while R1 and R2 are standard resistors. The
supply voltage, VDD, is divided between R2 and the
parallel combination of RT1 and R1. For convenience,
the parallel combination of RT1 and R1 will be referred
to as RTEMP. The resistance of the thermistor at various
temperatures is obtained from the manufacturer’s
specifications. Thermistors are often referred to in
terms of their resistance at 25°C.
Generally, the thermistor shown in Figure 5-2 is a non-
linear device with a negative temperature coefficient
(also called an NTC thermistor). In Figure 5-2, R1 is
used to linearize the thermistor temperature response
and R2 is used to produce a positive temperature
coefficient at the VIN node. As an added benefit, this
configuration produces an output voltage delta of 1.4V,
which is well within the range of the VC(SPAN)
specification of the TC646. A 100 kΩ NTC thermistor is
selected for this application in order to keep IDIV at a
minimum.
For the voltage range at VIN to be equal to 1.25V to
2.65V, the temperature range of this configuration is
0°C to 50°C. If a different temperature range is required
from this circuit, R1 should be chosen to equal the
resistance value of the thermistor at the center of this
new temperature range. It is suggested that a maxi-
mum temperature range of 50°C be used with this cir-
cuit due to thermistor linearity limitations. With this
change, R2 is adjusted according to the following
equations:
TC646
EQUATION
VDD x R2
RTEMP (T1) + R2
= V(T1)
VDD x R2
RTEMP (T2) + R2
= V(T2)
Where T1 and T2 are the chosen temperatures and
RTEMP is the parallel combination of the thermistor
and R1.
These two equations facilitate solving for the two
unknown variables, R1 and R2. More information about
thermistors may be obtained from AN679, “Tempera-
ture Sensing Technologies”, and AN685, “Thermistors
In Single Supply Temperature Sensing Circuits”, which
can be downloaded from Microchip’s web site at
www.microchip.com.
5.2 Auto-Shutdown Temperature
Design
A voltage divider on VAS sets the temperature where
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 above is linearly
related to temperature, the shutdown temperature TAS
is related to T2 and T1 by:
EQUATION
2.65V - 1.25V = VAS - 1.25V
T2 - T1
TAS - T1
( )1.4V
VAS = T2 - T1
( TAS - T1) + 1.25V
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 VAS
voltage is:
EQUATION
1.4V
VAS = (125 - 0) (25 - 0) + 1.25V = 1.53V
The VAS voltage may be set using a simple resistor
divider as shown in Figure 5-3.
2002 Microchip Technology Inc.
DS21446C-page 11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet TC646.PDF ] | |
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