參數(shù)資料
型號(hào): MAX6653
廠商: Maxim Integrated Products, Inc.
英文描述: Temperature Monitors and PWM Fan Controllers
中文描述: 溫度監(jiān)視器和PWM風(fēng)扇控制器
文件頁(yè)數(shù): 12/24頁(yè)
文件大?。?/td> 297K
代理商: MAX6653
M
Temperature Monitors and
PWM Fan Controllers
12
______________________________________________________________________________________
measurement rate, which is controlled by bits [4:2] of
the fan-filter register (23h). Table 5 shows the effect of
the temperature measurement rate control bits. As an
example, assume that the temperature measurement
rate is 2Hz, or 0.5s per monitoring cycle, and the fan-fil-
ter rate is 0.416% per monitoring cycle. For the fan drive
to change from 50% to 100% requires 50% / 0.416% =
120 temperature monitoring cycles. Thus, for a tempera-
ture-monitoring cycle of 0.5s, the time required for the
drive to change from 50% to 100% is 60s.
Fan-Speed Measurement
The fan speed is measured by using the relatively slow
tachometer signal from the fan to gate an 11.25kHz
clock frequency into a fan-speed counter. The mea-
surement is initialized on the starting edge of a PWM
output if fan-speed measurement is enabled by setting
bit 2 of configuration register 2 (01h) to 1. Counting
begins on the leading edge of the second tachometer
pulse and lasts for two tachometer periods or until the
counter overranges (255). The measurement repeats
unless monitoring is disabled by resetting bit 2 in the
configuration register 2 (01h). The measured result is
stored in the fan-speed reading register (08h).
The fan-speed count is given by:
The fan-speed count is give67,
Count
RPM
where RPM = fan speed in RPM.
N determines the speed range and is programmed by
bits [7:6] in the fan characteristics register (20h) as
shown in Table 14. When the speed falls below the value
in the speed range column, a fan failure is detected.
The TACH/AIN input can be either a digital signal (from
the fan
s tachometer output) or an analog signal,
depending on the setting of bit 2 of the configuration
register 1 (00h). The default setting is zero, which sets
up TACH/AIN as a digital input. For the analog input
(Figure 4), the detected voltage threshold is typically at
250mV, which is appropriate for sensing the voltage of
a sense resistor connected to the ground lead of a 2-
wire fan. The AIN input only responds to pulse widths
greater than 10μs.
N
=
×
Table 12. Spin-Up Time; Bits [2:0] Fan
Characteristics Register (20h)
POR = 101
BIT 2
BIT 1
BIT 0
SPIN-UP
TIME (s)
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0.2
0.4
0.6
0.8
1
2
4
8
Table 13. Fan Filter Ramp Rate; Bits [6:5]
Fan Filter Register (23h)
POR = 10;
BIT 6
BIT 5
RAMP RATE
(x100% / 240)
RAMP RATE
(% DUTY CYCLE)
0
0
1
1
0
1
0
1
1
2
4
8
0.416
0.833
1.667
3.333
FAN CHARACTERISTICS REGISTER (20h) POR = 01
BIT 7
0
0
1
1
BIT 6
0
1
0
1
N
SPEED RANGE (FAIL SPEED)
(RPM)
1
2
4
8
2647
1324
662
331
Table 14. N Factor for Speed-Range Adjustment (Assuming Two Tachometer Pulses
per Revolution)
Figure 4. Simplified Tachometer Analog Input Structure
100
VREF 1
0.1
μ
F
TACH
INPUT
VREF 2
CLK
FF
MAX6653
MAX6663
MAX6664
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