TC646
+5V
V
DD
V
OUT
D
1
12.0V
Zener
R
2
*
2.2 kΩ
Fan
TC646
Q
1
*
GND
R
4
*
10 kΩ
R
3
*
2.2Ω
-12V
NOTE:
*Value depends on the specific application and is shown for example only.
FIGURE 5-8:
TABLE 5-2:
Device
MMBT2222A
MPS2222A
MPS6602
SI2302
MGSF1N02E
SI4410
SI2308
Power the Fan from a -12V Supply.
TRANSISTORS AND MOSFETS FOR Q
1
(V
DD
= 5V)
Package
SOT-23
TO-92
TO-92
SOT-23
SOT-23
SO-8
SOT-23
Max. V
BE(sat)
/V
GS
(V)
1.2
1.2
1.2
2.5
2.5
4.5
4.5
Min. H
FE
50
50
50
NA
NA
NA
NA
V
CEO
/V
DS
(V)
40
40
40
20
20
30
60
Fan Current
(mA)
150
150
500
500
500
1000
500
Suggested
R
BASE
(Ω)
800
800
301
Note 1
Note 1
Note 1
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
5.7
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, V
AS
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 V
DD
supply powers up first. If possible, the networks
attached to V
IN
and V
AS
should connect to the V
DD
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.
Power Supply Routing and
Bypassing
Noise present on the V
IN
and V
AS
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 V
IN
, which is usually driven
from a high impedance source (such as a thermistor).
In addition, the V
DD
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
MICROCHIP [ MICROCHIP TECHNOLOGY ]
