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参数资料
型号： TC642DEMO
厂商： Microchip Technology Inc.
英文描述： PWM Fan Speed Controller with FanSense⑩ Technology
中文描述： 与FanSense PWM风扇速度控制器⑩技术
文件页数： 11/28页
文件大小： 485K
代理商： TC642DEMO
2002 Microchip Technology Inc.
DS21444C-page 11
TC642
We can further specify R
1
and R
2
by the condition that
the divider voltage is equal to our desired V
MIN
. This
yields the following equation:
EQUATION
Solving for the relationship between R
1
and R
2
results
in the following equation:
EQUATION
In this example, R
1
= (1.762) R
2
. Substituting this rela-
tionship back into the previous equation yields the
resistor values:
R
2
= 18.1 k
, and R
1
= 31.9 k
In this case, the standard values of 31.6 k
and
18.2 k
are very close to the calculated values and
would be more than adequate.
5.3
Operations at Low Duty Cycle
One boundary condition which may impact the selec-
tion of the minimum fan speed is the irregular activation
of the Diagnostic Timer due to the TC642 “missing” fan
commutation pulses at low speeds. This is a natural
consequence of low PWM duty cycles (typically 25% or
less). Recall that the SENSE function detects commu-
tation of the fan as disturbances in the current through
R
SENSE
. These can only occur when the fan is ener-
gized (i.e., V
OUT
is “on”). At very low duty cycles, the
V
OUT
output is “off” most of the time. The fan may be
rotating normally, but the commutation events are
occurring during the PWM’s off-time.
The phase relationship between the fan’s commutation
and the PWM edges tends to “walk around” as the
system operates. At certain points, the TC642 may fail
to capture a pulse within the 32-cycle missing pulse
detector window. When this happens, the 3-cycle
Diagnostic Timer will be activated, the V
OUT
output will
be active continuously for three cycles and, if the fan is
operating normally, a pulse will be detected. If all is
well, the system will return to normal operation. There
is no harm in this behavior, but it may be audible to the
user as the fan accelerates briefly when the Diagnostic
Timer fires. For this reason, it is recommended that
V
MIN
be set no lower than 1.8V.
5.4
FanSense Network
(R
SENSE
and C
SENSE
)
The FanSense network, comprised of R
SENSE
and
C
SENSE
, allows the TC642 to detect commutation of
the fan motor (FanSense technology). This network
can be thought of as a differentiator and threshold
detector. The function of R
SENSE
is to convert the fan
current into a voltage. C
SENSE
serves to AC-couple this
voltage signal and provide a ground-referenced input to
the SENSE pin. Designing a proper SENSE network is
simply a matter of scaling R
SENSE
to provide the nec-
essary amount of gain (i.e., the current-to-voltage con-
version ratio). A 0.1 μF ceramic capacitor is
recommended for C
SENSE
. Smaller values require
larger sense resistors, and higher value capacitors are
bulkier and more expensive. Using a 0.1 μF capacitor
results in reasonable values for R
SENSE
. Figure 5-4
illustrates a typical SENSE network. Figure 5-5 shows
the waveforms observed using a typical SENSE net-
work.
FIGURE 5-4:
SENSE Network.
FIGURE 5-5:
SENSE Waveforms.
V
DD
x R
2
R
1
+ R
2
V
MIN
=
V
DD
- V
MIN
V
MIN
R
1
= R
2
x
Q
1
GND
V
DD
R
SENSE
SENSE
R
BASE
C
SENSE
(0.1
μ
F Typ.)
V
OUT
Fan
1
Ch1
100mV
Tek Run: 10.0kS/s Sample
Ch2
100mV
M5.00ms
Ch1
142mV
GND
[
T
]
T
Waveform @ Sense Resistor
90mV
50mV
GND
Waveform @ Sense Pin
2
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相关代理商/技术参数
参数描述
TC642DEMO 制造商:Microchip Technology Inc 功能描述:Tools Development kit For Use
TC642EOA 功能描述:马达/运动/点火控制器和驱动器 w/Fault Dtct RoHS:否 制造商:STMicroelectronics 产品:Stepper Motor Controllers / Drivers 类型:2 Phase Stepper Motor Driver 工作电源电压:8 V to 45 V 电源电流:0.5 mA 工作温度:- 25 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:HTSSOP-28 封装:Tube
TC642EOA713 功能描述:马达/运动/点火控制器和驱动器 w/Fault Dtct RoHS:否 制造商:STMicroelectronics 产品:Stepper Motor Controllers / Drivers 类型:2 Phase Stepper Motor Driver 工作电源电压:8 V to 45 V 电源电流:0.5 mA 工作温度:- 25 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:HTSSOP-28 封装:Tube
TC642EPA 制造商:MICROCHIP 制造商全称:Microchip Technology 功能描述:PWM Fan Speed Controller with FanSense⑩ Technology
TC642EUA 功能描述:马达/运动/点火控制器和驱动器 w/Fault Dtct RoHS:否 制造商:STMicroelectronics 产品:Stepper Motor Controllers / Drivers 类型:2 Phase Stepper Motor Driver 工作电源电压:8 V to 45 V 电源电流:0.5 mA 工作温度:- 25 C to + 125 C 安装风格:SMD/SMT 封装 / 箱体:HTSSOP-28 封装:Tube
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