MAX6641AUB92+【PDF 11/17 页】IC TEMP MONITOR SMBUS 10UMAX

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Sheet目录44

7页 8页 9页 10页 [11页]12页 13页 14页 15页

SMBus-Compatible Temperature Monitor with

Automatic PWM Fan-Speed Controller

______________________________________________________________________________________ 11

Fan Instantaneous Duty Cycle (0Ah)

Read the fan instantaneous duty-cycle register to deter-

mine the duty cycle at PWMOUT at any time. The POR

state of the fan instantaneous duty-cycle register is 00h.

Remote- and Local-Diode

Fan-Start Temperature (0Bh, 0Ch)

These registers contain the temperature threshold val-

ues at which fan control begins in automatic mode. See

the Automatic PWM Duty-Cycle Control section for

details on setting the fan-start thresholds. The POR

state of the remote- and local-diode fan-start tempera-

ture registers is 00h.

Fan Configuration (0Dh)

The fan-configuration register controls the hysteresis

level, temperature step size, and whether the remote or

local diode controls the PWMOUT signal; see Table 1.

Set bit D7 of the fan-configuration register to zero to set

the hysteresis value to 5癈. Set bit D7 to 1 to set the

hysteresis value to 10癈. Set bit D6 to zero to set the

fan-control temperature step size to 1癈. Set bit D6 to 1

to set the fan-control temperature step size to 2癈. Set

bit D5 to 1 to control the fan with the remote-diodes

temperature reading. Set bit D4 to 1 to control the fan

with the local-diodes temperature reading. If both bits

D5 and D4 are high, the device uses the highest PWM

value. If both bits D5 and D4 are zero, the MAX6641

runs in manual fan-control mode where only the value

written to the fan-target duty-cycle register (09h) con-

trols the PWMOUT duty cycle. In manual fan-control

mode, the value written to the fan-target duty-cycle reg-

ister is not limited by the value in the maximum duty-

cycle register. It is, however, clipped to 240 if a value

above 240 is written. The POR state of the fan-configu-

ration register is 00h.

Duty-Cycle Rate of Change (0Eh)

Bits D7, D6, and D5 of the duty-cycle rate-of-change

cycle. Each increment is 2/240 of the duty cycle; see

Table 3. This allows the time from 33% to 100% duty

cycle to be adjusted from 5s to 320s. The rate-of-

change control is always active in manual mode. To

make instant changes, set bits D7, D6, D5 = 000. The

POR state of the duty-cycle rate-of-change register is

A0h (1s time between increments).

Duty-Cycle Step Size (0Fh)

Bits D7D4 of the duty-cycle step-size register change

the size of the duty-cycle change for each temperature

step. The POR state of the duty-cycle step-size register

is 50h; see Table 4.

PWM Frequency Select (10h)

Set bits D7, D6, and D5 (select A, select B, and select

C) in the PWM frequency-select register to control the

PWMOUT frequency; see Table 5. The POR state of the

PWM frequency select register is 40h, 33Hz. The lower

frequencies are usually used when driving the fans

power-supply pin as in the Typical Application Circuit,

with 33Hz being the most common choice. The 35kHz

D7, D6, D5

TIME BETWEEN

INCREMENTS (s)

TIME FROM 33%

TO 100% (s)

000

001

0.0625

010

0.1250

011

0.2500

100

0.5000

101

1.0000

110

2.0000

160

111

4.0000

320

Table 3. Duty-Cycle Rate-of-Change

D7D4

CHANGE IN DUTY

CYCLE PER

TEMPERATURE STEP

TEMPERATURE RANGE

FOR FAN CONTROL

1?/SPAN>

TEP

T 1

0/240

N/A

2/240

80.00

4/240

40.00

6/240

26.67

8/240

20.00

1 1

10/240

16.00

12/240

13.33

111

14/240

11.43

16/240

10.00

1 1

18/240

8.89

1 1

20/240

8.00

1 11

22/240

7.27

24/240

6.67

11 1

26/240

6.15

111

28/240

5.71

1111

30/240

5.33

Table 4. Duty-Cycle Step-Size

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