ADM1034
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24
RPM = (81920 ?60) / 6143
Fan Speed = 800 RPM
Alarm Speed
The fan ALARM speed (Bit 6) in Status Register 3
(Address 0x51) is set whenever the fan runs at alarm speed.
This occurs if the device is programmed to run the fan at full
speed whenever the THERM
temperature limits are
exceeded. The device runs at alarm speed, for example, if the
Boost Disable bit (Bit 1) of the Configuration 2 Register
(Address 0x02) is not set to 1.
Fan Response Register
The ADM1034 fan speed controller operates by reading
the current fan speed, comparing it with the programmed fan
speed, and then updating the drive signal applied to the fan.
The rate at which the ADM1034 looks at and updates the
drive signal is determined by the fan response register.
Different fans have different inertias and respond to a
changing drive signal more or less quickly than others. The
fan response register allows the user to tailor the ADM1034
to a particular fan to prevent situations like overshoot.
The user programs the number of updates the ADM1034
can make to the drive signal per second. Table 27 lists the
available options.
Table 27. FAN RESPONSE CODES
Code
Update Rate
000
1.25 updates/second
001
2.5 updates/second = Default
010
5 updates/second
011
10 updates/second
100
20 updates/second
101
40 updates/second
110
80 updates/second
111
160 updates/second
Table 28. CONVERSION RATES
Bit #
Function
7
Reserved
<6:4>
Fan 2 Response
3
Reserved
<2:0>
Fan 1 Response
Look-up Table: Modes of Operation
The ADM1034 look-up table has two different modes of
operation used to determine the behavior of the system:
?SPAN class="pst ADM1034ARQZ-REEL_2295499_3"> Manual Mode
?SPAN class="pst ADM1034ARQZ-REEL_2295499_3"> Look-up Table
Manual Mode
In manual mode, the ADM1034 is under software control.
The software can program the required fan speed value or
the target fan speed to the ADM1034, which then outputs
that fan speed.
Programming Target Fan Speed
In this mode, the user programs the target fan speed as a
TACH count for N poles or a TACH count for one full
rotation of the fan, assuming the number of poles is
programmed correctly in the Configuration 3 Register
(Address 0x03).
Use the following steps to program the target fan speed:
1. Place the ADM1034 into manual mode. Set Bit 7
(Table/SW) of Configuration Register 1
(Address 0x01) = 0.
2. Program the target TACH count (fan speed) using
the following equation:
(eq. 4)
TACH Count + (f 60)R
where:
f = clock frequency = 81.92 kHz
R = required RPM value
Example 1: If the desired speed for Fan 1 is 5000 rpm,
program the following value to the TACH count registers:
TACH Count = (f ?60)/5000
TACH Count = 983d = 0x03D7
Example 2: If the desired speed for Fan 2 is 3500 rpm,
program the following value to the TACH pulse period
registers:
TACH Count = (f ?60)/3500
TACH Count = 1404d = 0x057C
Table 29. REGISTERS TO BE PROGRAMMED
Fan
Description
Address
Value
Fan 1
Look-up Table FS1, LSB
0x2A
0xD7
Fan 1
Look-up Table FS1, MSB
0x2B
0x03
Fan 2
Look-up Table FS2, LSB
0x2C
0x7C
Fan 2
Look-up Table FS2, MSB
0x2D
0x05
Look-up Table
The   ADM1034   allows   the   user   to   program   a
temperature-to-fan speed profile. There are 24 registers in
the look-up table; 8 for temperature and 16 for target fan
speed (each target fan speed is two registers). In total, there
are eight available points. In the default configuration, four
of these are for Fan 1 and four are for Fan 2. However, it can
be configured such that eight points are available and both
fans run from the same table.
There are two options when programming the look-up
table. The ADM1034 can be programmed to make the fan
speed run at discrete speeds and jump to the new fan speed
once the temperature threshold is crossed. Or, it can linearly
ramp the TACH count between the two temperature
thresholds.
Figure 40 and Figure 41 show what the look-up table
looks like if all eight points are used on the one curve for both
fans.
Figure 40 shows the transfer curve when the fan is
programmed to run at discrete speeds. The ADM1034 spins
the fan at its new speed once a threshold is crossed.