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参数资料
| 型号： | ADM1026JST |
| 厂商： | ON Semiconductor |
| 文件页数： | 24/55页 |
| 文件大小： | 0K |
| 描述： | IC CNTRL SYS REF/EEPROM 48LQFP |
| 产品变化通告： | MFG CHG Notification ADI to ON Semi Product Obsolescence 30/Sept/2009 |
| 标准包装： | 250 |
| 功能： | 硬件监控器 |
| 传感器类型： | 内部和外部 |
| 感应温度： | 0°C ~ 100°C |
| 精确度： | ±3°C（最小值） |
| 拓扑： | ADC，比较器，多路复用器，寄存器库 |
| 输出类型： | SMBus? |
| 输出警报： | 无 |
| 输出风扇： | 是 |
| 电源电压： | 3 V ~ 5.5 V |
| 工作温度： | 0°C ~ 100°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 48-LQFP |
| 供应商设备封装： | 48-LQFP（7x7） |
| 包装： | 管件 |
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ADM1026
12 V
V CC
22.5kHz
CLOCK
PULLUP
4.7k ?
TYP
FAN(0–7)
FAN SPEED
COUNTER
CONFIGURATION
REG. 1 BIT 0
1
2
3
4
FAN0
INPUT
* CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x V CC
1
2
3
4
2.0 V t V PULLUP
t 3.3 V STBY
R PULLUP ) R1 ) R2
Figure 44. Fan with Tach Pullup to Voltage > V CC
(e.g. 12 V), Clamped with Zener Diode
If the fan has a strong pullup (less than 1 k W ) to +12 V, or
a totem pole output, a series resistor can be added to limit the
Zener current, as shown in Figure 45. Alternatively, a
resistive attenuator may be used, as shown in Figure 47.
R1 and R2 should be chosen such that:
R2
(eq. 15)
START OF FAN0 FAN1
MONITORING MEASUREMENT MEASUREMENT
CYCLE PERIOD PERIOD
Figure 47. Fan Speed Measurement
The monitoring cycle begins when a 1 is written to the
monitor bit (Bit 0 of Configuration Register 1). The
INT_Enable (Bit 1) should be set to 1 to enable the INT
output.
The fan speed counter starts counting as soon as the fan
channel has been switched to. If the fan tach count reaches
12 V
V CC
0xFF, the fan has failed or is not connected. If a fan is
connected and running, the counter is reset on the second
tach rising edge, and oscillator pulses are actually counted
PULLUP TYP
<1 k ?
FAN(0–7)
FAN SPEED
COUNTER
from the second rising tach edge to the fourth rising edge.
The measurement then switches to the next fan channel.
Here again, the counter begins counting and is reset on the
second tach rising edge, and oscillator pulses are counted
* CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 x V CC
Figure 45. Fan with Strong Tach Pullup to >V CC or
Totem Pole Output, Attenuated with R1/R2
from the second rising edge to the fourth rising edge. This
is repeated for the other six fan channels.
Note that fan speed measurement does not occur until
1.8 seconds after the monitor bit has been set. This is to
12 V
V CC
allow the fans adequate time to spin up. Otherwise, the
ADM1026 could generate false fan failure interrupts.
<1 k ?
R1*
TACH
OUTPUT
FAN(0–7)
FAN SPEED
COUNTER
During the 1.8 second fan spin-up time, all fan tach registers
read 0x00.
To accommodate fans of different speed and/or different
numbers of output pulses per revolution, a prescaler
Count + 22.5
10 3 60
RPM
Divisor
* SEE TEXT
Figure 46. Fan with Strong Tach Pullup to > V CC or
Totem Pole Output, Clamped with Zener and Resistor
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
22.5 kHz oscillator into the input of an 8-bit counter for two
periods of the fan tach output, as shown in Figure 47, so the
accumulated count is actually proportional to the fan tach
period and inversely proportional to the fan speed.
(divisor) of 1, 2, 4, or 8 may be added before the counter.
Divisor values for Fans 0 to 3 are contained in the Fan 0–3
divisor register (Address 02h) and those for Fans 4 to 7 in the
Fan 4–7 divisor register (Address 03h). The default value
is 2, which gives a count of 153 for a fan running at
4400 RPM producing two output pulses per revolution. The
count is calculated by the equation:
(eq. 16)
For constant-speed fans, fan failure is typically
considered to have occurred when the speed drops below
70% of nominal, corresponding to a count of 219. Full scale
(255) is reached if the fan speed fell to 60% of its nominal
value. For temperature-controlled, variable-speed fans, the
situation is different.
http://onsemi.com
24
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