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| 型号： | ADT7468ARQ |
| 厂商： | ON Semiconductor |
| 文件页数： | 28/81页 |
| 文件大小： | 0K |
| 描述： | IC REMOTE THERMAL CTRLR 24-QSOP |
| 产品变化通告： | MFG CHG Notification ADI to ON Semi Product Obsolescence 11/Feb/2009 |
| 标准包装： | 56 |
| 系列： | dBCool® |
| 功能： | 风扇控制，温度监控器 |
| 传感器类型： | 内部和外部 |
| 感应温度： | -40°C ~ 120°C，外部传感器 |
| 精确度： | ±2°C（最小值） |
| 拓扑： | ADC，比较器，风扇速度计数器，多路复用器，寄存器库 |
| 输出类型： | SMBus? |
| 输出警报： | 无 |
| 输出风扇： | 是 |
| 电源电压： | 3 V ~ 5.5 V |
| 工作温度： | -40°C ~ 120°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 24-QSOP |
| 包装： | 管件 |
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ADT7468
ACTIVE COOLING
DRIVING THE FAN USING PWM CONTROL
The ADT7468 uses pulse-width modulation (PWM) to control
fan speed. This relies on varying the duty cycle (or on/off ratio)
of a square wave applied to the fan to vary the fan speed. The
external circuitry required to drive a fan using PWM control is
extremely simple. For 4-wire fans, the PWM drive might need
only a pull-up resistor. In many cases, the 4-wire fan PWM
input has a built-in pull-up resistor.
The ADT7468 PWM frequency can be set to a selection of low
frequencies or a single high PWM frequency. The low fre-
quency options are usually used for 2-wire and 3-wire fans,
while the high frequency option is usually used with 4-wire
fans.
For 2-wire or 3-wire fans, a single N-channel MOSFET is the
only drive device required. The specifications of the MOSFET
depend on the maximum current required by the fan being
driven and the input capacitance of the FET. Because a 10 k?
(or greater) resistor must be used as a PWM pull-up, an FET
Figure 34. Driving a 3-Wire Fan Using an N-Channel MOSFET
Figure 34 uses a 10 k? 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 ADT7468. If in
doubt as to whether the fan has an open-collector or totem-pole
TACH output, use one of the input signal conditioning circuits
shown in the Fan Speed Measurement section.
Figure 35 shows a fan drive circuit using an NPN transistor,
such as a general-purpose MMBT2222. While these devices are
inexpensive, they tend to have much lower current handling
capabilities and higher on resistance than MOSFETs. When
choosing a transistor, care should be taken to ensure that it
meets the fan’s current requirements. Ensure that the base
resistor is chosen such that the transistor is saturated when the
fan is powered on.
Because 4-wire fans are powered continuously, the fan speed is
not switched on or off as with previous PWM driven/powered
fans. This enables it to perform better than 3-wire fans,
especially for high frequency applications.
with large input capacitance can cause the PWM output to
become distorted and adversely affect the fan control range.
This is a requirement only when using high frequency
12V
10k ?
12V
PWM mode.
Typical notebook fans draw a nominal 170 mA, and so SOT
TACH
10k ?
4.7k ?
3.3V
TACH
12V
FAN
1N4148
devices can be used where board space is a concern. In
desktops, fans can typically draw 250 mA to 300 mA each. If
ADT7468
665 ?
you drive several fans in parallel from a single PWM output or
drive larger server fans, the MOSFET must handle the higher
current requirements. The only other stipulation is that the
PWM
Q1
MMBT2222
MOSFET should have a gate voltage drive, V GS < 3.3 V, for direct
interfacing to the PWM_OUT pin. V GS 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
significant voltage drop across the FET, which would reduce the
voltage applied across the fan and, therefore, the maximum
Figure 35. Driving a 3-Wire Fan Using an NPN Transistor
Figure 36 shows a typical drive circuit for 4-wire fans.
12V 12V
12V, 4-WIRE FAN
4.7k ?
operating speed of the fan.
Figure 34 shows how to drive a 3-wire fan using PWM control.
TACH/AIN
10k ?
10k ?
TACH
V CC
TACH
PWM
12V
10k ?
12V
ADT7468
3.3V
2k ?
TACH/AIN
10k ?
4.7k ?
12V
FAN
1N4148
PWM
3.3V
ADT7468
PWM
10k ?
Q1
NDT3055L
Rev. 3 | Page 28 of 81 | www.onsemi.com
Figure 36. Driving a 4-Wire Fan
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| ADT7468ARQ-REEL | 功能描述:IC REMOTE THERMAL CTRLR 24-QSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 热管理 系列:dBCool® 标准包装:1 系列:- 功能:温度监控系统（传感器） 传感器类型:内部和外部 感应温度:-40°C ~ 125°C，外部传感器 精确度:±2.5°C 本地（最大值），±5°C 远程（最大值） 拓扑:ADC，比较器，寄存器库 输出类型:2 线 SMBus? 输出警报:无 输出风扇:无 电源电压:2.7 V ~ 5.5 V 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:SOT-23-8 供应商设备封装:SOT-23-8 包装:Digi-Reel® 其它名称:296-22675-6 |
| ADT7468ARQ-REEL7 | 功能描述:IC REMOTE THERMAL CTRLR 24-QSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 热管理 系列:dBCool® 标准包装:1 系列:- 功能:温度监控系统（传感器） 传感器类型:内部和外部 感应温度:-40°C ~ 125°C，外部传感器 精确度:±2.5°C 本地（最大值），±5°C 远程（最大值） 拓扑:ADC，比较器，寄存器库 输出类型:2 线 SMBus? 输出警报:无 输出风扇:无 电源电压:2.7 V ~ 5.5 V 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:SOT-23-8 供应商设备封装:SOT-23-8 包装:Digi-Reel® 其它名称:296-22675-6 |
| ADT7468ARQZ | 功能描述:板上安装温度传感器 RMT THRM CTR VLT MON RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| ADT7468ARQZ-REEL | 功能描述:板上安装温度传感器 RMT THRM CTR VLT MON RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| ADT7468ARQZ-REEL7 | 功能描述:IC REMOTE THERMAL CTRLR 24QSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热管理 系列:dBCool® 标准包装:1 系列:- 功能:温度监控系统（传感器） 传感器类型:内部和外部 感应温度:-40°C ~ 125°C，外部传感器 精确度:±2.5°C 本地（最大值），±5°C 远程（最大值） 拓扑:ADC，比较器，寄存器库 输出类型:2 线 SMBus? 输出警报:无 输出风扇:无 电源电压:2.7 V ~ 5.5 V 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:SOT-23-8 供应商设备封装:SOT-23-8 包装:Digi-Reel® 其它名称:296-22675-6 |
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