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ADM1034

Rev. 0 | Page 29 of 40

Once the temperature exceeds the highest temperature point in

the look-up table, the fan speed remains at the highest speed

until the temperature drops below the T7 temperature value.

When the look-up table is split in two, the same applies.

If the temperatures in T1 to T8 are not programmed in

succession, the fan speed moves to the next highest pro-

grammed temperature as the temperature increases. Similarly,

when the temperature decreases, it ignores programmed higher

temperatures and jumps to the next lower temperature. There-

fore, the temperature-to-fan-speed profile for increasing and

decreasing temperature can be different.

When programming the look-up table, the user has the option

to use between two and eight points for each fan (eight points

only if the same curve is to be used for both fans). If the user

just wants to program a transfer curve (and knows the starting

temperature, minimum speed, maximum temperature, and

maximum speed), then all the user needs to program are four

parameters—T1, T2, FS1, and FS2. The remainder of the look-

up temperature thresholds should remain at their default values

of +191°C. If required, the FS3 should be programmed with the

same value as FS2 to give the flat curve, if required. Or, the fan

speeds can be left at the default value of 0. However, it is normal

to program a THERM limit as well. Once this temperature is

exceeded and the boost bit is set, the fans run to full speed. This

overrides the look-up table.

FAN SPEED

T (3 TO 8) =

°C

TEMPERATURE

TACH COUNT 2 TO 8

TACH COUNT 1

Figure 43. Programming Two Points on the Look-Up Table

Table 29. Look-Up Table Register Addresses

Temperature, x

FSx, LSB

FSx, MSB

0x22

0x2A

0x2B

0x23

0x2C

0x2D

0x24

0x2E

0x2F

0x25

0x30

0x31

0x26

0x32

0x33

0x27

0x34

0x35

0x28

0x36

0x37

0x29

0x38

0x39

SETTING UP THE SIZE OF THE LOOK-UP TABLE

When 4:8 Look-Up (Bit 3)is set to 0 (default), four points are

used for each fan.

When 4:8 Look-Up (Bit 3) is set to 1, all eight points on the

table are used for both fans.

SETTING UP THE LOOK-UP TABLE IN

LINEAR MODE

When Discrete/Linear Speed (Bit 2) is set to 1 (default), the

TACH count decreases linearly (and therefore the fan speed

increases) with temperature.

Example: At temperature TX, the fans run at FSX and fan speed

increases with temperature to FSX+1 at temperature TX+1.

Alternatively, the fan can be run at discrete fan speeds. When

Discrete/Linear Speed (Bit 2) is set to 0, the fan runs at a new

speed once the temperature threshold is exceeded.

SETTING WHICH TEMPERATURE

CHANNEL CONTROLS A FAN

Fan Behavior Register (Address 0x07)

Bits <1:0> = DRIVE1 Behavior (D1B)

Bits <3:2> = DRIVE2 Behavior (D2B)

The ADM1034 can be configured so that Fan 1 or Fan 2 can be

controlled by either the local temperature, or by the Remote 1

or Remote 2 temperatures.

Table 30. Drive X BHVR Bits

Bits

DRIVE x BHVR

Local Temperature Controls Fan x

Remote 1 Temperature Controls Fan x

Remote 2 Temperature Controls Fan x

Fan x Runs at Full Speed

By default, Remote 1 controls Fan 1, and Remote 2 controls

Fan 2. If the ADM1034 is in single-channel mode and one of the

fans is set up to run from a temperature channel that is not being

measured, the drive X BHVR bits are set to 11 and the fan is run

at full speed.

LOOK-UP TABLE HYSTERESIS

The user can program a hysteresis to be applied to the look-up

table. The advantage of this is apparent if the temperature is

cycling around one of the threshold temperatures and causing

the fan speed to switch between the two speeds, particularly

when the look-up table is configured in discrete mode. It would

not be as important in the linear mode.

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