NCT7491
http://onsemi.com
31
allows TACH readings to be taken on a continuous basis for
fans connected directly to a dc source. For 4wire fans, once
high frequency mode is enabled, the dc bits do not need to
be set because this is automatically done internally.
If any tach channels are not connected then the associated
DC bit should be set for that fan.
Calculating Fan Speed From Register Values
Assuming a fan with a two pulses per revolution, and with
the NCT7491 programmed to measure two pulses per
revolution, fan speed is calculated by Fan Speed (RPM) =
(78,000 x 60)/Fan TACH Reading where Fan TACH
Reading is the 16bit fan tachometer reading.
Example:
TACH1 High Byte (Register 0x29) = 0x17
TACH1 Low Byte (Register 0x28) = 0xFF
What is Fan 1 speed in RPM?
Fan 1 TACH Reading = 0x17FF = 6143 (decimal)
RPM = (f x 60)/Fan 1 TACH Reading
RPM = (78000 x 60)/6143
Fan Speed = 762 RPM
Fan Pulses per Revolution
Different fan models can output one, two, three, or four
TACH pulses per revolution. Once the number of fan TACH
pulses has been determined, it can be programmed into the
TACH pulses per revolution register (0x7B) for each fan.
Alternatively, this register can be used to determine the
number or pulses per revolution output by a given fan. By
plotting fan speed measurements at 100% speed with
different pulses per revolution setting, the smoothest graph
with the lowest ripple determines the correct pulses per
revolution value.
TACH Pulses per Revolution Register 0x7B
" Bits [1:0], FAN1 default = 2 pulses per revolution
" Bits [3:2], FAN2 default = 2 pulses per revolution
" Bits [5:4], FAN3 default = 2 pulses per revolution
" Bits [7:6], FAN4 default = 2 pulses per revolution
" 00 = 1 pulse per revolution
" 01 = 2 pulses per revolution
" 10 = 3 pulses per revolution
" 11 = 4 pulses per revolution
Fan SpinUp
The NCT7491 has a unique fan spinup function. It spins
the fan at 100% PWM duty cycle until two TACH pulses are
detected on the TACH input. When two TACH pulses have
been detected, the PWM duty cycle goes to the expected
running value, for example, 33%. The advantage of this is
that fans have different spinup characteristics and take
different times to overcome inertia. The NCT7491 runs the
fans just fast enough to overcome inertia and is quieter on
spinup than fans programmed to spin up for a given
spinup time.
Fan Startup Timeout
To prevent the generation of false interrupts as a fan spins
up, because the fan is below running speed, the NCT7491
includes a fan startup timeout function. During this time, the
NCT7491 looks for two TACH pulses. If two TACH pulses
are not detected, an interrupt is generated. Fan startup
timeout can be disabled by setting Bit 3 (FSPDIS) of
Configuration Register 7 (0x11).
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
NCT75MNR2G
IC SENSOR TEMP DGTL 8DFN
NCV8881PWR2G
IC REG TRPL BUCK/LINEAR 16SOIC
NE1617ADS,112
IC TEMP MONITOR 16SSOP
NE1619DS,118
IC TEMP MONITOR 16SSOP
NIS5112D1R2G
IC ELECTRONIC FUSE HOTSWAP 8SOIC
NIS5132MN2TXG
IC ELECTRONIC FUSE 12V 10DFN
NIS5132MN3TXG
IC ELECTRONIC FUSE 12V 10-DFN
NSI45015WT1G
IC LED DRIVER LINEAR SOD-123
相关代理商/技术参数
NCT75DMR2G
功能描述:板上安装温度传感器 2-Channel Digital Thermometer w/ Alarm
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
NCT75DR2G
功能描述:板上安装温度传感器 2-Channel Digital Thermometer w/ Alarm
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
NCT75MNR2G
功能描述:板上安装温度传感器 HAS2MONOJLCC84SPACE
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
NCT7717U TR
制造商:Nuvoton Technology Corp 功能描述:SMBUS INTERFACE TEMP. SENSOR W 制造商:Nuvoton Technology Corp 功能描述:IC SMBUS TEMP SENSOR 8MSOP
NCT7718W TR
制造商:Nuvoton Technology Corp 功能描述:IC SMBUS TEMP SENSOR 8MSOP
NCT7802Y
制造商:Nuvoton Technology Corp 功能描述:
NCT7904D
制造商:Nuvoton Technology Corp 功能描述:IC H/W MONITOR
NCT80DBR2G
功能描述:板上安装温度传感器 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
