TC648B Microchip Technology Inc., TC648B Datasheet - Page 22

• Manufacturer Part Number: TC648B
• Description: Pwm Fan Speed Controllers With Auto-shutdown, Fan Restart And Fansense Technology For Fault Detection
• Manufacturer: Microchip Technology Inc.

TC646B/TC648B/TC649B
FIGURE 5-7:
TABLE 5-2:
5.6
The bias supply (V
TC649B devices should be bypassed with a 1.0 µF
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 TC646B/TC648B/
TC649B device ground, individual ground returns for
the TC646B/TC648B/TC649B and the low side of the
fan current sense resistor should be used.
DS21755B-page 22
Note 1:
MGSF1N02E
MMBT2222A
MPS2222A
MPS6602
Device
SI2302
SI4410
SI2308
2:
IN
Bias Supply Bypassing and Noise
Filtering
pin controls the duty cycle in a linear fashion,
A series gate resistor may be used in order to control the MOSFET turn-on and turn-off times.
These drive devices are suggestions only. Fan currents listed are for individual fans.
FAN DRIVE DEVICE SELECTION TABLE (NOTE 2)
IN
V
pin should be bypassed with a
DD
OUT
Package
Output Drive Device Configurations.
SOT-23
SOT-23
SOT-23
SOT-23
a) Single Bipolar Transistor
TO-92
TO-92
SO-8
) for the TC646B/TC648B/
R
BASE
Max Vbe sat /
Vgs(V)
1.2
1.2
1.2
2.5
2.5
4.5
4.5
Fan Bias
FAN
GND
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, system cooling is no longer required,
so the fan is to be turned off. Prior to turn-off, 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 that is directly in the inlet air stream. The
thermistor is a NTC, 100 k
part number NHQ104B425R5. The given Beta for the
thermistor is 4250. The system bias voltage to run the
fan controller is 5V, while the fan voltage is 12V.
V
OUT
b) N-Channel MOSFET
V
Design Example/Typical
Application
CE
(V)
40
40
40
20
20
30
60
/V
DS
Fan Bias
FAN
GND
Fan Current
2003 Microchip Technology Inc.
R
(mA)
1000
Q
150
150
500
500
500
500
SENSE
@ 25ºC, Thermometrics
1
Suggested
Rbase ( )
Note 1
Note 1
Note 1
Note 1
800
800
301
®