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參數(shù)資料
| 型號(hào)： | ADT7470ARQZ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 7BIT(s), RECTANGULAR, SURFACE MOUNT |
| 封裝： | ROHS COMPLIANT, MO-137AB, QSOP-16 |
| 文件頁數(shù)： | 13/40頁 |
| 文件大?。?/td> | 962K |
| 代理商： | ADT7470ARQZ |
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ADT7470
Rev. C | Page 20 of
40
FAN DRIVE USING PWM CONTROL
The ADT7470 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. Two
main control schemes are used: low frequency and high fre-
quency PWM.
Configuration Register 1 Bit[6], at address 0x40, configures the
fan drive for high or low frequency operation. If this bit is set to
0, which is the default, high frequency fan drive is selected. If
this bit is set to 1, low frequency fan drive is selected. All four
PWM outputs on the ADT7470 have the same drive frequency.
HIGH FREQUENCY FAN DRIVE
One of the important features of fan controllers is the PWM
drive frequency. Most fans are driven asynchronously at low
frequency (30 Hz to 100 Hz). Increasingly, the devices drive
fans at greater than 20 kHz. These controllers are meant to drive
4-wire fans with PWM control built-in internal to the fan in
Figure 17. The ADT7470 supports high frequency PWM (great
than 20 kHz), as well as 1.4 kHz and other low frequency PWM.
This allows the user to drive 3-wire or 4-wire fans.
If using 3-wire fans this mode, care should be taken to ensure
that incomplete tach information does not occur at low PWM
duty cycles, or short PWM pulse widths.
V
PWM
3.3V
10k
Ω
TACH
ADT7470
12V
10k
Ω
TACH
10k
Ω
4.7k
Ω
1N4148
04684-0-024
GND
PWM_IN
Figure 17. Driving a 4-Wire Fan
LOW FREQUENCY FAN DRIVE
For low frequency, low-side drive, the external circuitry required
to drive a fan using PWM control is extremely simple. A single
NMOS FET is the only drive device required. The specifications
of the MOSFET depend on the maximum current required by
the fan being driven. Typical notebook fans draw a nominal
170 mA; therefore, SOT devices can be used where board space
is a concern. In desktops, fans can typically draw 250 mA to
300 mA each. If the user needs to drive several fans in parallel
from a single PWM output or drive larger server fans, the
MOSFET needs to handle the higher current requirements. The
only other stipulation is that the MOSFET should have a gate
voltage drive, VGS, less than 3.3 V, for direct interfacing to the
PWM pin of the ADT7470. VGS of the chosen MOSFET can be
greater than 3.3 V as long as the pull-up on its 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. This
would reduce the voltage applied across the fan and, therefore,
the maximum operating speed of the fan.
Figure 18 shows how a 3-wire fan can be driven using low
frequency PWM control where the control method is low-side,
low frequency switching.
Figure 18 shows the ideal interface when interfacing a tach
signal from a 12 V fan (or greater voltage) to a 5 V (or less)
logic device. In all cases, the tach signal from the fan must be
kept below 5 V maximum to prevent damage to the ADT7470.
The three resistors in Figure 18 ensure that the tach voltage
is kept within safe levels for typical desktop and notebook
systems.
12V
Q1
NDT3055L
PWM
3.3V
10k
Ω
12V
FAN
TACH/AIN
ADT7470
12V
10k
Ω
TACH
10k
Ω
4.7k
Ω
1N4148
04684-
0-
022
Figure 18. Driving a 3-Wire Fan Using an N-Channel MOSFET
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相關(guān)代理商/技術(shù)參數(shù) |
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| ADT7470ARQZ-REEL | 功能描述:IC SENSOR TEMP FAN CTRLR 16QSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:SilentSense™ 功能:溫度監(jiān)控系統(tǒng)（傳感器） 傳感器類型:內(nèi)部和外部 感應(yīng)溫度:-55°C ~ 125°C，外部傳感器 精確度:±2°C 本地（最大），±3°C 遠(yuǎn)程（最大） 拓?fù)?ADC（三角積分型），比較器，寄存器庫 輸出類型:I²C?/SMBus? 輸出警報(bào):是 輸出風(fēng)扇:是 電源電壓:2.7 V ~ 5.5 V 工作溫度:-55°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:8-MSOP 包裝:帶卷 (TR) 其它名稱:MIC284-2BMMTRMIC284-2BMMTR-ND |
| ADT7470ARQZ-REEL7 | 功能描述:IC SENSOR TEMP FAN CTRLR 16QSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:SilentSense™ 功能:溫度監(jiān)控系統(tǒng)（傳感器） 傳感器類型:內(nèi)部和外部 感應(yīng)溫度:-55°C ~ 125°C，外部傳感器 精確度:±2°C 本地（最大），±3°C 遠(yuǎn)程（最大） 拓?fù)?ADC（三角積分型），比較器，寄存器庫 輸出類型:I²C?/SMBus? 輸出警報(bào):是 輸出風(fēng)扇:是 電源電壓:2.7 V ~ 5.5 V 工作溫度:-55°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:8-TSSOP，8-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:8-MSOP 包裝:帶卷 (TR) 其它名稱:MIC284-2BMMTRMIC284-2BMMTR-ND |
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