參數(shù)資料
型號: ADM1026JST-REEL
廠商: ANALOG DEVICES INC
元件分類: 電源管理
英文描述: Complete Thermal and System Management Controller
中文描述: 4-CHANNEL POWER SUPPLY SUPPORT CKT, PQFP48
封裝: 7 X 7 MM, 1.40 MM HEIGHT, PLASTIC, MS-026BBC, LQFP-48
文件頁數(shù): 24/56頁
文件大小: 634K
代理商: ADM1026JST-REEL
ADM1026
Automatic Fan Speed Control
The ADM1026 offers a simple method of controlling fan speed
according to temperature without intervention from the host
processor. Monitoring must be enabled by setting Bit 0 of
Configuration Register 1 (Address 00h), to enable automatic fan
speed control. Automatic fan speed control can be applied to the
DAC output, the PWM output, or both, by setting Bit 5 and/or
Bit 6 of Configuration Register 1.
Rev. A | Page 24 of 56
The T
MIN
registers (Addresses 10h to 12h) contain minimum
temperature values for the three temperature channels (on-chip
sensor and two remote diodes). This is the temperature at which
a fan starts to operate when the temperature sensed by the
controlling sensor exceeds T
MIN
. T
MIN
can be the same or
different for all three channels. T
MIN
is set by writing a twos
complement temperature value to the T
MIN
registers. If any
sensor channel is not required for automatic fan speed control,
T
MIN
for that channel should be set to 127°C (01111111).
In automatic fan speed control mode, (as shown Figure 42 and
Figure 43) the four MSBs of the DAC control register (Address
04h) and PWM control register (Address 05h) set the minimum
values for the DAC and PWM outputs. Note that, if both DAC
control and PWM control are enabled (Bits 5 and 6 of
Configuration Register 1 = 1), the four MSBs of the DAC
control register (Address 04h) define the minimum fan speed
values for both the DAC and PWM outputs. The value in the
PWM control register (Address 05h) has no effect.
Minimum DAC Code DAC
MIN
= 16 ×
D
256
5
=
Code
Voltage
Output
DAC
×
Minimum PWM Duty Cycle PWMMIN
= 6.67 ×
D
where
D
is the decimal equivalent of Bits 7 to 4 of the register.
When the temperature measured by any of the sensors exceeds
the corresponding T
MIN
, the fan is spun up for 2 seconds with
the fan drive set to maximum (full scale from the DAC or 100%
PWM duty cycle). The fan speed is then set to the minimum as
previously defined. As the temperature increases, the fan drive
increases until the temperature reaches T
MIN
+ 20°C.
The fan drive at any temperature up to 20°C above T
MIN
is
given by
(
)
20
100
MIN
T
ACTUAL
MIN
MIN
T
PWM
PWM
PWM
×
+
=
or
(
)
20
240
MIN
T
ACTUAL
T
MIN
MIN
DAC
DAC
DAC
×
+
=
For simplicity of the automatic fan speed algorithm, the DAC
code increases linearly up to 240, not its full scale of 255.
However, when the temperature exceeds T
MIN
+20°C, the DAC
output jumps to full scale. To ensure that the maximum cooling
capacity is always available, the fan drive is always set by the
sensor channel demanding the highest fan speed.
If the temperature falls, the fan does not turn off until the
temperature measured by all three temperature sensors has
fallen to their corresponding T
MIN
4°C. This prevents the fan
from cycling on and off continuously when the temperature is
close to T
MIN
.
Whenever a fan starts or stops during automatic fan speed
control, a one-off interrupt is generated at the INT output. This
is described in more detail in the section on the ADM1026
Interrupt Structure.
PWM
OUTPUT
MIN
TEMPERATURE
T
MIN
SPIN UP FOR 2 SECONDS
100%
T
MIN
– 4°C
T
MIN
+ 20°C
0
Figure 42. Automatic PWM Fan Control Transfer Function
DAC
OUTPUT
MIN
TEMPERATURE
T
MIN
255
T
MIN
– 4°C
T
MIN
+ 20°C
SPIN UP FOR 2 SECONDS
240
0
Figure 43. Automatic DAC Fan Control Transfer Function
Fan Inputs
Pins 3 to 6 and 9 to 12 may be configured as fan speed
measuring inputs by clearing the corresponding bit(s) of
Configuration Register 2 (Address 01h), or as general-purpose
logic inputs/outputs by setting bits in this register. The power-
on default value for this register is 00h, which means all the
inputs are set for fan speed measurement.
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