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參數(shù)資料
| 型號： | ADM1031ARQ |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | DIGITAL TEMP SENSOR-SERIAL, 11BIT(s), 3Cel, RECTANGULAR, SURFACE MOUNT |
| 封裝： | MO-137AB, QSOP-16 |
| 文件頁數(shù)： | 20/35頁 |
| 文件大?。?/td> | 368K |
| 代理商： | ADM1031ARQ |
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ADM1031
Rev. 3 | Page 27 of 35 | www.onsemi.com
02402-
037
Figure 37. Fan Speed Sensing Waveform at TACH/AIN Pin
FAN SPEED MEASUREMENT
The fan counter does not count the fan tach output pulses
directly, because the fan speed can 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 11.25 kHz oscillator into the
input of an 8-bit counter. The fan speed measuring circuit is
initialized on the rising edge of a PWM high output if fan speed
measurement is enabled (Bit 2 and Bit 3 of Configuration
Register 2 = 1). It then starts counting on the rising edge of the
second tach pulse and counts for two fan tach periods, until the
rising edge of the fourth tach pulse, or until the counter
overranges if the fan tach period is too long. The measurement
cycle repeats until monitoring is disabled. The fan speed
measurement is stored in the fan speed reading register at
address 0×08, 0×09.
The fan speed count is given by:
Count = (f × 60)/R × N
where:
f = 11.25 kHz
R = fan speed in RPM.
N = speed range (either 1, 2, 4, or 8)
The frequency of the oscillator can be adjusted to suit the
expected running speed of the fan by varying N, the speed
range. The oscillator frequency is set by Bit 7 and Bit 6 of Fan
Characteristics Register 1 (0×20) and Fan Characteristics
Register 2 (0×21) as shown in Table 15. Figure 38 shows how
the fan measurements relate to the PWM_OUT pulse trains.
Table 15. Oscillator Frequencies
Bit 7
Bit 6
N
Oscillator Frequency (kHz)
0
1
11.25
0
1
2
5.625
1
0
4
2.812
1
8
1.406
CLOCK
CONFIG 2
REG. BIT 2
FAN
INPUT
START OF
MONITORING
CYCLE
FAN
MEASUREMENT
PERIOD
02402-
038
Figure 38. Fan Speed Measurement
In situations where different output drive circuits are used for
fan drive, it can be desirable to invert the PWM drive signal.
Setting Bit 3 of Configuration Register 1 (0×00) to 1, inverts the
PWM_OUT signal. This makes the PWM_OUT pin high for
100% duty cycle. Bit 3 of Configuration Register 1 should gener-
ally be set to 1 when using an n-MOS device to drive the fan.
If using a p-MOS device, Bit 3 of Configuration Register 1
should be cleared to 0.
FAN FAULTS
The FAN_FAULT output (Pin 8) is an active-low, open-drain
output used to signal fan failure to the system processor. Writing
a Logic 1 to Bit 4 of Configuration Register 1 (0×00) enables the
FAN_FAULToutput pin. The FAN_FAULT output is enabled by
default. The FAN_FAULT output asserts low only when five
consecutive interrupts are generated by the ADM1031 device due
to the fan running underspeed, or if the fan is completely stalled.
Note that the Fan Tach High Limit must be exceeded by at least
one before a FAN_FAULT can be generated. For example, if we
are only interested in getting a FAN_FAULT if the fan stalls, then
the fan speed value is 0×FF for a failed fan. Therefore, we should
make the Fan Tach High Limit = 0×FE to allow FAN_FAULT to
be asserted after five consecutive fan tach failures.
Figure 39 shows the relationship between INT, FAN_FAULT,
and the PWM drive channel. The PWM_OUT channel is
driving a fan at some PWM duty cycle, 50% for example, and
the fan’s tach signal (or fan current for a 2-wire fan) is being
monitored at the TACH/AIN pin. Tach pulses are being
generated by the fan, during the high time of the PWM duty
cycle train. The tach is pulled high during the off time of the
PWM train because the fan is connected high-side to the n-
MOS device.
Suppose the fan has twice previously failed its fan speed
measurement. Looking at Figure 39, PWM_OUT is brought high
for two seconds, to restart the fan if it has stalled. Sometime later
a third tach failure occurs. This is evident by the tach signal being
low during the high time of the PWM pulse, causing the fan
speed reading register to reach its maximum count of 255. Since
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| ADM1031ARQ-REEL | 功能描述:IC SENSOR 2-TEMP/FAN CTRL 16QSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 熱管理 系列:- 標(biāo)準(zhǔn)包裝:1 系列:- 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:-40°C ~ 125°C，外部傳感器 精確度:±2.5°C 本地（最大值），±5°C 遠(yuǎn)程（最大值） 拓?fù)?ADC，比較器，寄存器庫 輸出類型:2 線 SMBus? 輸出警報:無 輸出風(fēng)扇:無 電源電壓:2.7 V ~ 5.5 V 工作溫度:-40°C ~ 125°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-8 供應(yīng)商設(shè)備封裝:SOT-23-8 包裝:Digi-Reel® 其它名稱:296-22675-6 |
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