TC649 Microchip, TC649 Datasheet - Page 13

• Manufacturer Part Number: TC649
• Description: PWM Fan Speed Controller
• Manufacturer: Microchip

Table 5-2 gives examples of some commonly available
transistors and MOSFETs. This table should be used
as a guide only since there are many transistors and
MOSFETs which will work just as well as those listed.
The critical issues when choosing a device to use as
Q1 are: (1) the breakdown voltage (V
(MOSFET)) must be large enough to withstand the
highest voltage applied to the fan (Note: This will occur
when the fan is off); (2) 5 mA of base drive current must
FIGURE 5-6:
TABLE 5-2:
MMBT2222A
MPS2222A
MPS6602
SI2302
MGSF1N02E
SI4410
SI2308
Note 1: A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.
V OUT
2002 Microchip Technology Inc.
Device
a) Single Bipolar Transistor
R
BASE
TRANSISTORS AND MOSFETS FOR Q
Package
SOT-23
SOT-23
SOT-23
SOT-23
TO-92
TO-92
SO-8
Output Drive Transistor Circuit Topologies.
V
GND
Fan
DD
R
Q
SENSE
1
Max. V
(BR)CEO
V
OUT
BE(sat)
(V)
1.2
1.2
1.2
2.5
2.5
4.5
4.5
or V
/V
R
BASE
GS
b) Darlington Transistor Pair
DS
Min. H
NA
NA
NA
NA
50
50
50
be enough to saturate the transistor when conducting
the full fan current (transistor must have sufficient
gain); (3) the V
ficiently drive the gate of the MOSFET to minimize the
R
be within the transistor's/MOSFET's current handling
capability; and (5) power dissipation must be kept
within the limits of the chosen device.
FE
1
DS(on)
Q
(V
V
1
GND
Fan
DD
DD
V
CEO
R
of the device; (4) rated fan current draw must
Q
SENSE
= 5V)
(V)
40
40
40
20
20
30
60
2
/V
DS
OUT
voltage must be high enough to suf-
Fan Current
V
OUT
(mA)
1000
150
150
500
500
500
500
C) N-Channel MOSFET
DS21449C-page 13
TC649
Suggested
R
BASE
V DD
Note 1
Note 1
Note 1
Note 1
GND
Fan
800
800
301
R
Q
( )
SENSE
1