ADM1024ARUZ-REEL7 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
生产厂家
ADM1024ARUZ-REEL7 Datasheet PDF : 32 Pages
| |||
ADM1024
12V
VCC
12V
VCC
PULL-UP
4.7k⍀
TYP
FAN1 OR
FAN2
TACH.
OUTPUT
160k⍀
FAN SPEED
COUNTER
Figure 10a. Fan with Tach. Pull-Up to +VCC
If the fan output has a resistive pull-up to 12 V (or other voltage
greater than 6.5 V), the fan output can be clamped with a Zener
diode, as shown in Figure 10b. The Zener voltage should be
chosen so it is greater than VIH but less than 6.5 V, allowing for
the voltage tolerance of the Zener. A value of between 3 V
and 5 V is suitable.
12V
VCC
PULL-UP
4.7k⍀
TYP
FAN1 OR
FAN2
TACH.
OUTPUT
ZD1*
ZENER
160k⍀
FAN SPEED
COUNTER
*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8 ؋ VCC
Figure 10b. Fan with Tach. Pull-Up to Voltage
>6.5 V (e.g., 12 V ) Clamped with Zener Diode
If the fan has a strong pull-up (less than 1 kΩ) to 12 V, or a
totem-pole output, then a series resistor can be added to limit
the Zener current, as shown in Figure 10c. Alternatively, a
resistive attenuator may be used, as shown in Figure 10d.
R1 and R2 should be chosen such that:
( ) 2V <VPULL−UP × R2 / RPULL−UP + R1 + R2 < 5V
The fan inputs have an input resistance of nominally 160 kΩ to
ground, so 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 kΩ,
suitable values for R1 and R2 would be 100 kΩ and 47 kΩ. This
will give a high input voltage of 3.83 V.
12V
VCC
PULL-UP
TYP. <1k⍀
OR TOTEM-POLE
R1
10k⍀
TACH.
OUTPUT
FAN1 OR
FAN2
ZD1*
ZENER
FAN SPEED
COUNTER
160k⍀
*CHOOSE ZD1 VOLTAGE APPROXIMATELY. 0.8 ؋ VCC
Figure 10c. Fan with Strong Tach. Pull-Up to >VCC or
Totem-Pole Output, Clamped with Zener and Resistor
<1k⍀
FAN1 OR
R1*
FAN2
TACH.
OUTPUT
R2*
160k⍀
FAN SPEED
COUNTER
*SEE TEXT
Figure 10d. Fan with Strong Tach. Pull-Up to >VCC or
Totem-Pole Output, Attenuated with R1/R2
FAN SPEED MEASUREMENT
The fan counter does not count the fan tachometer 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 mea-
sured by gating an on-chip 22.5 kHz oscillator into the input
of an 8-bit counter for two periods of the fan tachometer out-
put, as shown in Figure 11; the accumulated count is actually
proportional to the fan tachometer period and inversely propor-
tional to the fan speed.
22.5kHz
CLOCK
CONFIG.
REG. 1 BIT 0
FAN1
INPUT
FAN2
INPUT
FAN1
MEASUREMENT
PERIOD
FAN2
MEASUREMENT
PERIOD
START OF
MONITORING
CYCLE
Figure 11. Fan Speed Measurement
The monitoring cycle begins when a one is written to the Start
Bit (Bit 0), and a zero to the INT_Clear Bit (Bit 3) of the
Configuration Register. INT_Enable (Bit 1) should be set to
one to enable the INT output. The measurement begins on the
rising edge of a fan tachometer pulse, and ends on the next-but-
one rising edge. The fans are monitored sequentially, so if only
one fan is monitored the monitoring time is the time taken after
the Start Bit for it to produce two complete tachometer cycles or
for the counter to reach full scale, whichever occurs sooner. If
more than one fan is monitored, the monitoring time depends
on the speed of the fans and the timing relationship of their
tachometer pulses. This is illustrated in Figure 12. Once the
fan speeds have been measured, they will be stored in the
Fan Speed Value Registers and the most recent value can be
read at any time. The measurements will be updated as long
as the monitoring cycle continues.
To accommodate fans of different speed and/or different num-
bers of output pulses per revolution, a prescaler (divisor) of 1, 2,
4, or 8 may be added before the counter. The default value is 2,
which gives a count of 153 for a fan running at 4400 rpm, pro-
ducing two output pulses per revolution.
The count is calculated by the equation:
( ) Count = 22.5 × 103 × 60 / (rpm × Divisor)
REV. B
–17–
Share Link: 