參數(shù)資料
型號(hào)： ADM1027ARQZ-RL7
廠商： ON Semiconductor
文件頁(yè)數(shù)： 23/56頁(yè)
文件大?。?/td> 1822K
描述： IC REMOTE THERMAL CTLR 24QSOP
產(chǎn)品變化通告： MFG CHG Notification ADI to ON Semi
Product Discontinuation Notice 25/Aug/2008
Product Obsolescence 30/Sept/2009
標(biāo)準(zhǔn)包裝： 1,000
系列： dBCool®
功能： 風(fēng)扇控制，溫度監(jiān)控器
傳感器類(lèi)型： 內(nèi)部和外部
感應(yīng)溫度： 0°C ~ 105°C，外部傳感器
精確度： ±1°C
拓?fù)洌?/td> ADC，比較器，風(fēng)扇速度計(jì)數(shù)器，多路復(fù)用器，寄存器庫(kù)
輸出類(lèi)型： SMBus?
輸出警報(bào)： 無(wú)
輸出風(fēng)扇： 是
電源電壓： 3 V ~ 5.5 V
工作溫度： 0°C ~ 105°C
安裝類(lèi)型： 表面貼裝
封裝/外殼： 24-SSOP（0.154"，3.90mm 寬）
供應(yīng)商設(shè)備封裝： 24-QSOP
包裝： 帶卷 (TR)
REV. A
ADM1027
23
FAN SPEED MEASUREMENTS
TACH Inputs
Pins 11, 12, 9, and 14 are open-drain TACH inputs intended
for fan speed measurement.
Signal conditioning in the ADM1027 accommodates the slow
rise and fall times typical of fan tachometer outputs. The maxi-
mum input signal range is 0 V to 5 V, even where V
CC
 is less
than 5 V. In the event that these inputs are supplied from fan
outputs that exceed 0 V to 5 V, either resistive attenuation of
the fan signal or diode clamping must be included to keep
inputs within an acceptable range.
Figures 25a to 25d show circuits for most common fan TACH
outputs. If the fan TACH output has a resistive pull-up to V
CC
, it
can be connected directly to the fan input, as shown in Figure 25a.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP
4.7k
TYP
V
CC
FAN
Figure 25a.  Fan With TACH Pull-Up to +V
CC
If the fan output has a resistive pull-up to 12 V (or other voltage
greater than 5 V), then the fan output can be clamped with a
Zener diode, as shown in Figure 25b. The Zener diode voltage
should be chosen so that it is greater than V
IH
 of the TACH
input but less than 5 V, allowing for the voltage tolerance of the
Zener. A value of between 3 V and 5 V is suitable.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP
4.7k
TYP
V
CC
FAN
ZD1*
*CHOOSE ZD1 VOLTAGE APPROX 0.8 V
CC
Figure 25b. Fan with TACH Pull-Up to Voltage
> 5 V (e.g., 12 V) Clamped with Zener Diode
If the fan has a strong pull-up (less than 1 k) to 12 V, or a
totem-pole output, then a series resistor can be added to limit
the Zener current, as shown in Figure 25c. Alternatively, a
resistive attenuator may be used, as shown in Figure 25d.
R1 and R2 should be chosen such that
 
 
2
2
1
2    5
V   V
R    R
R
R
V
PULLUP
PULLUP
<
?/DIV>
+
+
(
)
>
The fan inputs have an input resistance of nominally 160 kW to
ground; this should be taken into account when calculating
resistor values.
With a pull-up voltage of 12 V and pull-up resistor less than
1 kW, suitable values for R1 and R2 would be 100 kW and
47 kW. This will give a high input voltage of 3.83 V.
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP TYP
<1k
OR
TOTEM POLE
V
CC
FAN
ZD1*
*CHOOSE ZD1 VOLTAGE APPROX 0.8 V
CC
R1
10k
Figure 25c.  Fan with Strong TACH Pull-Up to > V
CC
 or
Totem-Pole Output, Clamped with Zener and Resistor
5V OR 12V
ADM1027
FAN SPEED
COUNTER
TACH X
TACHO
OUTPUT
PULL-UP TYP
<1k
V
CC
FAN
R2*
*SEE TEXT
R1*
Figure 25d.  Fan with Strong TACH Pull-Up to > V
CC
or Totem-Pole Output, Attenuated with R1/R2
Fan Speed Measurement
The fan counter does not count the fan TACH output pulses
directly because the fan speed may be less than 1000 RPM and
it would take several seconds to accumulate a reasonably large
and accurate count. Instead, the period of the fan revolution is
measured by gating an on-chip 90 kHz oscillator into the input
of a 16-bit counter for N periods of the fan TACHO output
(Figure 26), so the accumulated count is actually proportional
to the fan tachometer period and inversely proportional to the
fan speed.
1
2
3
4
LOCK
PWM
TACH
Figure 26. Fan Speed Measurement
N, the number of pulses counted, is determined by the settings
of Register 0x7B (fan pulses per revolution register). This register
contains two bits for each fan, allowing 1, 2 (default), 3, or 4
TACH pulses to be counted.
Rev. 3 | Page 23 of 56 | www.onsemi.com
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