TC647(2002) View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC647 Datasheet PDF : 28 Pages
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TC647
VDD
VDD
VDD
Fan
Fan
Fan
VOUT
RBASE
RBASE
VOUT
Q1
RSENSE
Q1
Q2
VOUT
RSENSE
Q1
RSENSE
GND
a) Single Bipolar Transistor
GND
b) Darlington Transistor Pair
GND
C) N-Channel MOSFET
FIGURE 5-7:
Output Drive Transistor Circuit Topologies.
+5V
VDD
VOUT
TC647
GND
R2 *
2.2 kΩ
D1
12.0V
Zener
Fan
Q1 *
R4 *
10 kΩ
R3 *
2.2 Ω
-12V
*Note: Value depends on the specific application and is shown for example only.
FIGURE 5-8:
-12V Supply.
Powering the Fan from a
ing points can result in enough parasitic capacitance
and/or inductance in the power supply connections to
delay one power supply “routing” versus another.
5.7 Power Supply Routing and
Bypassing
Noise present on the VIN and VMIN inputs may cause
erroneous operation of the FAULT output. As a result,
these inputs should be bypassed with a 0.01 µF capac-
itor mounted as close to the package as possible. This
is particularly true of VIN, which is usually driven from a
high impedance source (such as a thermistor). In addi-
tion, the VDD input should be bypassed with a 1 µF
capacitor. Ground should be kept as short as possible.
To keep fan noise off the TC647 ground pin, individual
ground returns for the TC647 and the low side of the
fan current sense resistor should be used.
Design Example
5.6 Latch-Up Considerations
As with any CMOS IC, the potential exists for latch-up
if signals are applied to the device which are outside
the power supply range. This is of particular concern
during power-up if the external circuitry (such as the
sensor network, VMIN divider or shutdown circuit) is
powered by a supply different from that of the TC647.
Care should be taken to ensure that the TC647’s VDD
supply powers up first. If possible, the networks
attached to VIN and VMIN should connect to the VDD
supply at the same physical location as the IC itself.
Even if the IC and any external networks are powered
by the same supply, physical separation of the connect-
Step 1. Calculate R1 and R2 based on using an NTC
having a resistance of 10 kΩ at TMIN (25°C)
and 4.65 kΩ at TMAX (45°C) (see Figure 5-9).
R1 = 20.5 kΩ
R2 = 3.83 kΩ
Step 2. Set minimum fan speed VMIN = 1.8V.
Limit the divider current to 100 µA from which
R5 = 33 kΩ and R6 = 18 kΩ
Step 3. Design the output circuit.
Maximum fan motor current = 250 mA.
Q1 beta is chosen at 50 from which
R7 = 800Ω.
DS21447C-page 14
2002 Microchip Technology Inc.
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