Rainbow-electronics MAX6640 Bedienungsanleitung PDF herunterladen (Seite 14)

MAX6640

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

Selects the temperature channel(s) that control the

PWM output when the MAX6640 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

• 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 2

shows the internal clock frequency as a function of

the range.)

Fan 1 and 2 Configuration 2a (11h and 15h)

The following registers apply to the automatic RPM

control mode:

• D[7:4]: Fan RPM (Tachometer) Step-Size A.

Selects the number of tachometer counts the target

value decreases for each temperature step increase

above the fan-start temperature. Value = n + 1 (1

through 16) where n is the value of D[7:4].

• D[3:2]: Temperature Step Size. Selects the temper-

ature increment for fan control. For each temperature

step increase, the target tachometer count decreas-

es by the value selected by D[7:4] (Table 7).

• D1: PWM Output Polarity. PWM output is low at

100% duty cycle when this bit is set to zero. PWM

output is high at 100% duty cycle when this bit is set

to 1.

• D0: Minimum Speed. Selects the value of the mini-

mum fan speed (when temperature is below the fan-

start temperature in the automatic RPM control

mode). Set to zero for 0% fan drive. Set to 1 to deter-

mine the minimum fan speed by the tachometer

count value in registers 22h and 23h (fan maximum

TACH).

2-Channel Temperature Monitor with Dual

Automatic PWM Fan-Speed Controller

14 ______________________________________________________________________________________

A C T U A L R A T E O F CH A N G E AT SPEC IF I C PW M FREQUENCIES

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 0.06 0.06 0.05 5

010 0.125 0.13 0.12 0.12 0.15 10

011 0.25 0.25 0.26 0.24 0.25 20

100 0.5 0.5 0.5 0.51 0.5 40

101 1 1 1 0.99 1 80

110 2 2 2 1.98 2 160

111 4 4 4 3.96 4 320

Table 4. Fan Duty-Cycle Rate-of-Change

D[1:0] FAN MAXIMUM RPM VALUE

00 2000

01 4000

10 8000

11 16,000

Table 5. 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 2 3Ch

4000 1000 2 2 78h

4000 3000 2 2 28h

4000 3000 2 4 14h

16,000 8000 4 4 3Ch

16,000 8000 4 2 78h

Table 6. 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)

1 2 ... 9 10 11 12 13 14 15 16 17 18 19 20 21 22

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