MAX6664AEE+T【PDF 11/24 页】IC TEMP MON FAN CNTRL 16-QSOP

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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

Temperature Monitors and

PWM Fan Controllers

______________________________________________________________________________________ 11

Automatic Fan-Control Mode

Automatic fan-speed control is selected by setting bits

[7:5] of configuration register 1 (00h) to 100 (to control

speed based on the remote temperature) or 101 (to

control speed based on both remote and local temper-

ature). Program a threshold, or starting temperature

TMIN, and the desired temperature range, T

RANGE

, into

the local temp T

MIN

RANGE

temperature and into the remote temp T

MIN

RANGE

11). If the fan control responds to both local and remote

temperatures, the higher PWM duty cycle has priority.

When the temperature exceeds T

MIN

, the fan is

enabled at a minimum duty cycle programmed in bits

[3:0] of the fan-speed configuration register (22h). The

duty cycle increases in proportion to the temperature

difference and reaches 100% at a temperature equal to

MIN

+ T

RANGE

). A hysteresis of 5癈 is built into the

MIN

set point to prevent the fan from starting and stop-

ping when the temperature is at the set point.

Spin-Up

To ensure proper fan startup, the MAX6653/MAX6663/

MAX6664 can be set to drive the fan to 100% duty

cycle for a short period on startup, and then revert to

the correct duty cycle. The spin-up time is programmed

by bits [2:0] in the fan characteristics register (20h).

The spin-up feature can be disabled by setting bit 7 of

the fan-filter register (23h) to 1; POR value is zero.

Table 12 shows programming of the spin-up time.

Fan-Filter Mode

When the MAX6653/MAX6663/MAX6664 are used for

automatic fan-speed control, the fan-filter mode helps

minimize the audible effects of varying fan speeds. The

fan-filter mode limits the rate at which fan speed can

change. Each time a new temperature measurement is

made, the fan-filter mode allows the PWM duty cycle to

increment by a selectable amount. The duty cycle can

change by 1/240, 2/240, 4/240, or 8/240 (0.416%,

0.833%, 1.667%, or 3.333%) of the PWM period after

each temperature-monitoring cycle. This prevents sud-

den changes in fan speed, even when temperature

changes suddenly.

The filter mode is set by bit 0 of the fan-filter register

(23h). To enable the fan-filter mode, write a 1 to this bit.

Bits [6:5] of the same register control the size of the

PWM steps.

Note that the rate of change depends on both the value

selected by the fan-filter bits and on the temperature

BITS [3:0] OF FAN-SPEED

CONFIGURATION REGISTER (22h)

BIT 3

BIT 2

BIT 1

BIT 0

% DUTY

CYCLE (%)

100

Table 9. Setting PWM Duty Cycle

Table 10. T

RANGE

Fan-Control Temperature

Range Bits [2:0] T

MIN

RANGE

Registers

(24h and 25h)POR = 001

BIT 2

BIT 1

BIT 0

TEMPERATURE

RANGE (?/SPAN>C)

Table 11.T

MIN

Fan-Control Start

Temperature; Bits [7:3] T

MIN

RANGE

Registers (24hPOR = 01000 and

25hPOR = 01100

BIT 7

BIT 6

BIT5

BIT 4

BIT3

MSB = +64癈

LSB = +4癈

Min threshold = 0癈

Max threshold = +127癈

LSB/step size = +4癈

POR = +48癈 or 01100b

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