TC642B View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC642B Datasheet PDF : 36 Pages
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TC642B/TC647B
Fan Bias
Fan Bias
FAN
FAN
VOUT
RBASE
Q1
RSENSE
VOUT
Q1
RSENSE
GND
a) Single Bipolar Transistor
GND
b) N-Channel MOSFET
FIGURE 5-7:
Output Drive Device Configurations.
TABLE 5-2: FAN DRIVE DEVICE SELECTION TABLE (NOTE 2)
Device
Package
Max Vbe sat /
Vgs(V)
Min hfe
VCE/VDS
(V)
Fan Current Suggested
(mA)
Rbase ()
MMBT2222A
SOT-23
1.2
50
40
150
MPS2222A
TO-92
1.2
50
40
150
MPS6602
TO-92
1.2
50
40
500
SI2302
SOT-23
2.5
NA
20
500
MGSF1N02E
SOT-23
2.5
NA
20
500
SI4410
SO-8
4.5
NA
30
1000
SI2308
SOT-23
4.5
NA
60
500
Note 1: A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.
2: These drive devices are suggestions only. Fan currents listed are for individual fans.
800
800
301
Note 1
Note 1
Note 1
Note 1
5.6 Bias Supply Bypassing and Noise
Filtering
The bias supply (VDD) for the TC642B/TC647B devices
should be bypassed with a 1.0 F ceramic capacitor.
This capacitor will help supply the peak currents that
are required to drive the base/gate of the external fan
drive devices.
As the VIN pin controls the duty cycle in a linear fashion,
any noise on this pin can cause duty-cycle jittering. For
this reason, the VIN pin should be bypassed with a
0.01 µF capacitor.
In order to keep fan noise off of the TC642B/TC647B
device ground, individual ground returns for the
TC642B/TC647B and the low side of the fan current
sense resistor should be used.
5.7 Design Example/Typical
Application
The system has been designed with the following
components and criteria.
System inlet air ambient temperature ranges from 0ºC
to 50ºC. At 20ºC and below, it is desired to have the
system cooling stay at a constant level. At 20ºC, the fan
should be run at 40% of its full fan speed. Full fan
speed should be reached when the ambient air is 40ºC.
The system has a surface mount, NTC-style thermistor
in a 1206 package. The thermistor is mounted on a
daughtercard, which is directly in the inlet air stream.
The thermistor is a NTC, 100 k @ 25ºC, Thermomet-
rics® part number NHQ104B425R5. The given Beta for
the thermistor is 4250. The system bias voltage to run
the fan controller is 5V and the fan voltage is 12V.
2002-2013 Microchip Technology Inc.
DS21756C-page 21
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