参数资料
型号: ADM1027ARQ-REEL
厂商: ON Semiconductor
文件页数: 31/56页
文件大小: 1822K
描述: IC REMOTE THERMAL CTRLR 24-QSOP
产品变化通告: MFG CHG Notification ADI to ON Semi
Product Discontinuation Notice 25/Aug/2008
标准包装: 2,500
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: 0°C ~ 105°C,外部传感器
精确度: ±1°C
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:
输出风扇:
电源电压: 3 V ~ 5.5 V
工作温度: 0°C ~ 105°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: 带卷 (TR)
REV. A
ADM1027
31
Step 4
Determine PWM
MIN
 for Each PWM (Fan) Output
PWM
MIN
 is the minimum PWM duty cycle that each fan in the
system will run at. It is also the start speed for each fan under
automatic fan control once the temperature rises above T
MIN
.
For maximum system acoustic benefit, PWM
MIN
 should be as
low as possible. Starting the fans at higher speeds than necessary
will merely make the system louder than needed. Depending on
the fan used, the PWM
MIN
 setting should be in the range 20%
to 33% duty cycle. This value can be found through
fan validation.
TEMPERATURE
T
MIN
100%
PWM
MIN
0%
Figure 30. PWM
MIN
 Determines Minimum PWM Duty Cycle
It is important to note that more than one PWM output can be
controlled from a single temperature measurement channel. For
example, Remote 1 temperature can control PWM1 and PWM2
outputs. If two different fans are used on PWM1 and PWM2,
then the fan characteristics can be set up differently. So Fan 1
driven by PWM1 can have a different PWM
MIN
 value than
that of Fan 2 connected to PWM2. Figure 31 illustrates this as
PWM1
MIN
 (front fan) is turned on at a minimum duty cycle of
20%, whereas PWM2
MIN
 (rear fan) turns on at a minimum of
40% duty cycle. Note however, that both fans turn on at the
exact same temperature, defined by T
MIN
.
TEMPERATURE
T
MIN
100%
PWM1
MIN
0%
P
W
M
1
P
W
M
2
PWM2
MIN
Figure 31. Operating Two Different Fans from a
Single-Temperature Channel
Programming the PWM
MIN
 Registers
The PWM
MIN
 registers are 8-bit registers that allow the minimum
PWM duty cycle for each output to be configured anywhere
from 0% to 100%. This allows minimum PWM duty cycle to be
set in steps of 0.39%.
The value to be programmed into the PWM
MIN
 register is
given by
 
 
Value  decimal
PWM
MIN
(
)
=
0 39
.
Example 1: For a minimum PWM Duty Cycle of 50%,
Value (decimal) = 50/0.39 = 128 decimal
Value = 128 decimal or 80 hex
Example 2: For a minimum PWM duty cycle of 33%,
Value (decimal) = 33/0.39 = 85 decimal
Value = 85 decimal or 54 hex
PWM
MIN
 Registers
Reg. 0x64 PWM1 Minimum Duty Cycle = 0x80 (50% default)
Reg. 0x65 PWM2 Minimum Duty Cycle = 0x80 (50% default)
Reg. 0x66 PWM3 Minimum Duty Cycle = 0x80 (50% default)
Fan Speed and PWM Duty Cycle
Note that PWM duty cycle does not directly correlate to fan
speed in rpm. Running a fan at 33% PWM duty cycle does not
equate to running the fan at 33% speed. Driving a fan at 33%
PWM duty cycle actually runs the fan at closer to 50% of its full
speed. This is because fan speed in %rpm relates to the square
root of PWM duty cycle. Given a PWM square wave as the
drive signal, fan speed in RPM equates to
 
 
% fan speed
PWM duty cycle
=
?0
Rev. 3 | Page 31 of 56 | www.onsemi.com
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