MAX6639 datasheet(14/22 Pages) MAXIM | 2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller

Part #	MAX6639

Description	2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller

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Manufacturer	MAXIM [Maxim Integrated Products]

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Fan 1 and 2 Configuration 1 (10h and 14h)

The following registers control the modes of operation

of the MAX6639:

• D7: PWM Mode. D7 = 1 sets the fan into manual

PWM duty-cycle control mode. Write the target duty

cycle in the fan duty-cycle register. D7 = 0 puts the

fan into RPM control mode. To set RPM manually, set

both fan-control temperature channels (bits D2 and

D3) to zero and write the desired tachometer count

into the TACH count register.

• D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4]

sets the time between increments of the duty cycle.

Each increment is 1/120 of the duty cycle. By adjust-

ing the rate-of-change, audibility of fan-speed

changes can be traded for response time. Table 5

shows the effect of D[6:4] and, for reference, the

time required for the fan speed to change from 33%

to 100% duty cycle as a function of the rate-of-

change bits.

• D[3:2]: Temperature Channel(s) for Fan Control.

Selects the temperature channel(s) that control the

PWM output when the MAX6639 is in automatic RPM

control mode (PWM mode bit is zero). If two chan-

nels are selected, the fan goes to the higher of the

two possible speeds. If neither channel is selected,

then the fan is in manual RPM mode and the speed

is forced to the value written to the target tach count

register 22h or 23h.

• D[1:0]: RPM Range. Scales the tachometer counter

by setting the maximum (full-scale) value of the RPM

range to 2000, 4000, 8000, or 16,000. (Table 3

shows the internal clock frequency as a function of

the range.)

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

14

______________________________________________________________________________________

ACTUAL RATE OF CHANGE AT SPECIFIC PWM FREQUENCIES

REGISTER 10h

OR 14h D[6:4]

NOMINAL RATE

OF CHANGE (s)

100Hz (s)

50Hz (s)

33.3Hz (s)

20Hz (s)

NOMINAL TIME FROM

33% TO 100% (s)

000

0

0000

0

001

0.0625

0.06

0.05

5

010

0.125

0.13

0.12

0.15

10

011

0.25

0.26

0.24

0.25

20

100

0.5

0.51

0.5

40

101

1

0.99

1

80

110

2

1.98

2

160

111

4

3.96

4

320

Table 5. Fan Duty-Cycle Rate-of-Change

REGISTER 10h OR 14h

FAN MAXIMUM RPM VALUE

00

2000

01

4000

10

8000

11

16,000

Table 6. Fan RPM Speed

MAXIMUM RPM VALUE

ACTUAL RPM

SELECTED NUMBER

OF PULSES PER

REVOLUTION

ACTUAL FAN PULSES

PER REVOLUTION

TACHOMETER COUNT

VALUE*

2000

1000

2

3Ch

4000

1000

2

78h

4000

3000

2

28h

4000

3000

2

4

14h

16,000

8000

4

3Ch

16,000

8000

4

2

78h

Table 7. RPM-to-Tachometer Count Relationship Examples

*Tachometer count value = ((internal clock frequency) x 60) / actual RPM) (selected number of pulses per revolution / actual fan pulses)

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