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參數(shù)資料
| 型號： | ADT7462ACPZ-500RL7 |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 8BIT(s), 4Cel, SQUARE, SURFACE MOUNT |
| 封裝： | 5 X 5 MM, LFCSP-32 |
| 文件頁數(shù)： | 25/88頁 |
| 文件大?。?/td> | 836K |
| 代理商： | ADT7462ACPZ-500RL7 |
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ADT7462
Rev. 2 | Page 31 of 88 | www.onsemi.com
FAN CONTROL
FAN DRIVE USING PWM CONTROL
The ADT7462 uses pulse-width modulation (PWM) to control
fan speed. Control relies on varying the duty cycle (or on/off
ratio) of a square wave applied to the fan to vary the fan speed.
The advantage of using PWM control is that it uses a very
simple external circuit. The specific circuit used depends upon
the type of fan.
There are three main fan types in use: 2-wire fans, 3-wire fans,
and 4-wire fans. The 2-wire fan has only power and ground
connections. The 3-wire fan has power and ground connections
and a TACH output to indicate the speed of the fan. The 4-wire
fan has power and ground connections, a TACH output, and a
PWM input. The PWM input is connected directly to the
PWM drive of the ADT7462 and is used to control the speed
of the fans.
For 2-wire and 3-wire fans, the low frequency PWM drive
signal should be selected. For 4-wire fans, the high frequency
PWM drive signal should be selected.
Using the ADT7462 with 2-Wire Fans
Figure 40 shows the most typical circuit used with a 2-wire
fan and illustrates how a 2-wire fan can be connected to the
ADT7462. The low frequency PWM mode must be selected
when using a 2-wire fan.
ADT7462
PWM
TACH
5V OR
12V FAN
Q1
NDT3055L
3.3V
+V
10k
TYPICAL
1N4148
0.01μF
RSENSE
2
TYPICAL
05
569-
030
Figure 40. Driving a 2-Wire Fan
Using the ADT7462 with 3-Wire Fans
Figure 41 shows the most typical circuit used with a 3-wire fan.
ADT7462
TACH/AIN
PWM
12V
FAN
Q1
NDT3055L
3.3V
12V
10k
4.7k
10k
1N4148
055
69-
031
Figure 41. Driving a 3-Wire Fan
The external circuitry required is very simple. A MOSFET, such
as the NDT3055L, is used as the pass device. The specifications
of the MOSFET depend on the maximum current required by
the fan being driven. A typical PC fan can draw a nominal cur-
rent ranging from a few hundred milliamps to over an amp of
current. Depending on the current rating of the fan, a SOT
device can be used where board space is a concern. If several
fans in parallel are driven from a single PWM output or if larger
server fans are driven, the MOSFET must handle the higher
current requirements. The only other stipulation is that the
MOSFET should have a gate voltage drive, VGS < 3.3 V, for direct
interfacing to the PWM pins. VGS can be greater than 3.3 V as
long as the pull-up on the gate is tied to 5 V. The MOSFET
should also have a low on resistance to ensure that there is not a
significant voltage drop across the FET, which would reduce the
voltage applied across the fan and reduce the full speed of the fan.
Figure 41 uses a 10 kΩ pull-up resistor for the TACH signal.
This assumes that the TACH signal is an open-collector from
the fan. In all cases, the TACH signal from the fan must be kept
below 5 V maximum to prevent damaging the ADT7462. If
in doubt as to whether the fan used has an open-collector or
totem-pole TACH output, use one of the input signal condition-
ing circuits shown in the Fan Speed Measurement section.
Driving a 3-wire fan with a PWM signal makes the fan speed
measurement more difficult because the TACH signal is
chopped by the PWM drive signal. Pulse stretching is required
in this case to make accurate fan speed measurements. For
more information, see the Fan Speed Measurement section.
Using the ADT7462 with 4-Wire Fans
Figure 42 shows the most typical circuit used with 4-wire fans.
ADT7462
TACH
PWM
12V, 4-WIRE FAN
3.3V OR 5V
12V 12V
2k
4.7k
10k
VCC
TACH
PWM
055
69-
032
Figure 42. Driving a 4-Wire Fan
Because the electronics in a 4-wire fan are powered continuously,
unlike previous PWM driven/powered fans, 4-wire fans tend to
perform better than 3-wire fans, especially for high frequency
applications. 4-wire frames also eliminate the requirement for
pulse stretching, because the TACH signal is always available.
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| ADT7462ACPZ-5RL7 | 功能描述:監(jiān)控電路 FLX H/WRE MON IC SRV RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| ADT7462ACPZ-R7 | 功能描述:監(jiān)控電路 FLX H/WRE MON IC SRV RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
| ADT7462ACPZ-REEL | 功能描述:監(jiān)控電路 FLX H/WRE MON IC SRV RoHS:否 制造商:STMicroelectronics 監(jiān)測電壓數(shù): 監(jiān)測電壓: 欠電壓閾值: 過電壓閾值: 輸出類型:Active Low, Open Drain 人工復(fù)位:Resettable 監(jiān)視器:No Watchdog 電池備用開關(guān):No Backup 上電復(fù)位延遲（典型值）:10 s 電源電壓-最大:5.5 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:UDFN-6 封裝:Reel |
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