ADM1031 datasheet(13/32 Pages) AD

13 / 32 page

REV. 0

ADM1031

–13–

Table V. Fan Spin-Up Times

Spin-Up Time

Bits 2:0

(Fan Characteristics Registers 1, 2)

000

200 ms

001

400 ms

010

600 ms

011

800 ms

100

1 sec

101

2 secs (Default)

110

4 secs

111

8 secs

Once the Automatic Fan Speed Control Loop parameters have been

chosen, the ADM1031 device may be programmed. The ADM1031

is placed into Automatic Fan Speed Control Mode by setting Bit 7

of Configuration Register 1 (Register 0x00). The device powers up

in Automatic Fan Speed Control Mode by default. The control

mode offers further flexibility in that the user can decide which

temperature channel/channels control each fan.

Table VI. Auto Mode Fan Behavior

Bits 6, 5

Control Operation (Config Register 1)

Remote Temp 1 Controls Fan 1. Remote Temp 2

Controls Fan 2.

Remote Temp 1 Controls Fans 1 and 2.

Remote Temp 2 Controls Fans 1 and 2.

Maximum Speed Calculated by Local and Remote

Temperature Channels Controls Fans 1 and 2.

When Bits 5 and 6 of Config Register 1 are both set to 1, it offers

increased flexibility. The local and remote temperature channels

can have independently programmed control loops with different

control parameters. Whichever control loop calculates the fastest fan

speed based on the temperature being measured, drives the fans.

Figure 9 shows how the fan’s PWM duty cycle is determined by

two independent control loops. This is the type of Auto Mode Fan

Behavior seen when Bits 5 and 6 of Config Register 1 are set to 11.

Figure 9a shows the control loop for the Local Temperature chan-

nel. Its TMIN value has been programmed to 20

°C, and its TRANGE

value is 40

°C. The local temperature’s TMAX will thus be 60°C.

Figure 9b shows the control loop for the Remote Temperature chan-

nel. Its TMIN value has been set to 0

°C, while its TRANGE = 80°C.

Therefore, the Remote Temperature’s TMAX value will be 80

°C.

Consider if both temperature channels measure 40

°C. Both control

loops will calculate a PWM duty cycle of 66%. Therefore, the fan

will be driven at 66% duty cycle.

If both temperature channels measure 20

°C, the local channel will

calculate 33% PWM duty cycle, while the Remote 1 channel will

calculate 50% PWM duty cycle. Thus, the fans will be driven at

50% PWM duty cycle. Consider the local temperature measuring

°C while the Remote 1 temperature is measuring 70°C. The

PWM duty cycle calculated by the local temperature control loop

will be 100% (since the temperature = TMAX). The PWM duty cycle

calculated by the Remote 1 temperature control loop at 70

°C will

be approximately 90%. So the fan will run full-speed (100% duty

cycle). Remember, that the fan speed will be based on the fastest

speed calculated, and is not necessarily based on the highest

temperature measured. Depending on the control loop param-

eters programmed, a lower temperature on one channel, may

actually calculate a faster speed, than a higher temperature on

the other channel.

LOCAL TEMPERATURE – C

100

TMIN

TMAX = TMIN + TRANGE

REMOTE TEMPERATURE – C

100

TMIN

T R

TMAX = TMIN + TRANGE

Figure 9. Max Speed Calculated by Local and Remote

Temperature Control Loops Drives Fan

PROGRAMMING THE AUTOMATIC FAN SPEED

CONTROL LOOP

1. Program a value for TMIN.

2. Program a value for the slope TRANGE.

3. TMAX = TMIN + TRANGE.

4. Program a value for Fan Spin-up Time.

5. Program the desired Automatic Fan Speed Control Mode

Behavior, i.e., which temperature channel controls the fan.

6. Select Automatic Fan Speed Control Mode by setting Bit 7

of Configuration Register 1.

OTHER CONTROL LOOP PARAMETERS

Having programmed all the above loop parameters, are there

any other parameters to worry about?

TMIN was defined as the temperature at which the fan switched

on and ran at minimum speed. This minimum speed is 33% duty

cycle by default. If the minimum PWM duty cycle is programmed

to 33%, the fan control loops will operate as previously described.

ADM1031 Datasheet(PDF) 13 Page - Analog Devices

ADM1031 Datasheet(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL