TC647B Microchip Technology Inc., TC647B Datasheet - Page 21

• Manufacturer Part Number: TC647B
• Description: Pwm Fan Speed Controllers With Minimum Fan Speed, Fan Restart And Fansense Technology For Fault Detection
• Manufacturer: Microchip Technology Inc.

FIGURE 5-7:
TABLE 5-2:
5.6
The bias supply (V
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 V
any noise on this pin can cause duty-cycle jittering. For
this reason, the V
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.
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.
2003 Microchip Technology Inc.
Device
2: These drive devices are suggestions only. Fan currents listed are for individual fans.
IN
Bias Supply Bypassing and Noise
Filtering
pin controls the duty cycle in a linear fashion,
FAN DRIVE DEVICE SELECTION TABLE (NOTE 2)
DD
IN
V
) for the TC642B/TC647B devices
pin should be bypassed with a
OUT
Package
Output Drive Device Configurations.
SOT-23
SOT-23
SOT-23
SOT-23
TO-92
TO-92
SO-8
a) Single Bipolar Transistor
R
BASE
Max Vbe sat /
Vgs(V)
1.2
1.2
1.2
2.5
2.5
4.5
4.5
Fan Bias
GND
FAN
R
Q
SENSE
1
Min hfe
NA
NA
NA
NA
50
50
50
5.7
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
the thermistor is 4250. The system bias voltage to run
the fan controller is 5V and the fan voltage is 12V.
V
®
OUT
part number NHQ104B425R5. The given Beta for
b) N-Channel MOSFET
V
Design Example/Typical
Application
CE
(V)
TC642B/TC647B
40
20
30
60
40
40
20
/V
DS
Fan Bias
FAN
Fan Current
GND
R
(mA)
1000
Q
150
150
500
500
500
500
SENSE
1
DS21756B-page 21
Suggested
Rbase ( )
Note 1
Note 1
Note 1
Note 1
800
800
301