TC647EOATR(2002) View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC647EOATR Datasheet PDF : 28 Pages
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TC647
VDD
Fan
VOH = 80% VDD
RBASE
+ VRBASE –
+ VBE(SAT) –
+
VRSENSE
–
Q1
RSENSE
The correct value for this resistor can be determined as
follows:
VOH
= VRSENSE + VBE(SAT) + VRBASE
VRSENSE = IFAN x RSENSE
VRBASE
= RBASE x IBASE
IBASE
= IFAN / hFE
VOH is specified as 80% of VDD in Section 1.0,
“Electrical Characteristics”; VBE(SAT) is given in the cho-
sen transistor data sheet. It is now possible to solve for
RBASE.
EQUATION
RBASE = VOH - VBE(SAT) - VRSENSE
IBASE
FIGURE 5-6:
RBASE.
GND
Circuit For Determining
Some applications require the fan to be powered from the
negative 12V supply to keep motor noise out of the
positive voltage power supplies. As shown in Figure 5-8,
zener diode D1 offsets the -12V power supply voltage,
holding transistor Q1 off when VOUT is low. When VOUT is
high, the voltage at the anode of D1 increases by VOUT
causing Q1 to turn on. Operation is otherwise the same as
the case of fan operation from +12V.
TABLE 5-2:
Device
TRANSISTORS AND MOSFETS FOR Q1 (VDD = 5V)
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.
2002 Microchip Technology Inc.
DS21447C-page 13
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