TC646 View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC646 Datasheet PDF : 28 Pages
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TC646
+5V
VDD
VOUT
TC646
R2*
2.2 kΩ
D1
12.0V
Zener
GND
R4*
10 kΩ
Fan
Q1*
R3*
2.2Ω
-12V
NOTE: *Value depends on the specific application and is shown for example only.
FIGURE 5-8:
Power the Fan from a -12V Supply.
TABLE 5-2: TRANSISTORS AND MOSFETS FOR Q1 (VDD = 5V)
Device
Package
Max. VBE(sat)/VGS
(V)
Min. HFE
VCEO/VDS
(V)
Fan Current
(mA)
Suggested
RBASE (Ω)
MMBT2222A
SOT-23
1.2
50
40
150
800
MPS2222A
TO-92
1.2
50
40
150
800
MPS6602
TO-92
1.2
50
40
500
301
SI2302
SOT-23
2.5
NA
20
500
Note 1
MGSF1N02E
SOT-23
2.5
NA
20
500
Note 1
SI4410
SO-8
4.5
NA
30
1000
Note 1
SI2308
SOT-23
4.5
NA
60
500
Note 1
Note 1: A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.
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, VAS divider or shutdown circuit) is
powered by a supply different from that of the TC646.
Care should be taken to ensure that the TC646’s VDD
supply powers up first. If possible, the networks
attached to VIN and VAS should connect to the VDD sup-
ply 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 connecting
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 VAS inputs may cause
erroneous operation of the FAULT output. As a result,
these inputs should be bypassed with a 0.01 µF
capacitor mounted as close to the package as possible.
This is especially true of VIN, which is usually driven
from a high impedance source (such as a thermistor).
In addition, the VDD input should be bypassed with a
1 µF capacitor. Grounds should be kept as short as
possible. To keep fan noise off the TC646 ground pin,
individual ground returns for the TC646 and the low
side of the fan current sense resistor should be used.
2002 Microchip Technology Inc.
DS21446C-page 15
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