Rainbow-electronics MAX6661 Manual de usuario descargar pdf (Pagina 17)

8415Hz is divided down from the MAX6661 internal

clock, and has a ±25°C tolerance.

1) Determine the fan’s maximum tachometer frequency:

(TACH)

Hz = (rpm/60s / min) ✕ number of poles

Where poles = number of pulses per revolution.

Most fans are two poles; therefore, they have two

pulses per revolution.

2) Set the programmable FTD so that the frequency of

the fan tachometer divided by the prescaler value in

the FCD register falls in the 33Hz to 66Hz range.

3) Determine the value required for the fan FS register:

FS = 8415 / (f

TACH

✕ P)

Where P is the prescaler division ratio of the FCD

Example: Fan A has a 2500rpm rating and 2 poles:

TACH

= 2500 / 60 ✕ 2 = 83.4Hz

MAX6661

Remote Temperature-Controlled Fan-Speed

Regulator with SPI-Compatible Interface

______________________________________________________________________________________ 17

TEMP DATA

FAN GAIN (FG)

8°C, 16°C, 32°C

RANGE

FAN-SPEED

CONTROL

1 TO 63

REF FREQ

8415Hz

FAN FULL

SCALE (FS)

127 TO 255

COUNTER

FAN

TACHOMETER

PERIOD (FTP)

FAN

TACHOMETER

PERIOD LIMIT (FTPL)

COMPARATOR

FAN TACHOMETER

DIVISOR (FTD)

1, 2, 4, 8

FAN OPEN/CLOSED

LOOP

UP/DOWN

DRIVER

DAC

FAN FAIL

FAN

TACH

FAN

TACH IN

Figure 7. MAX6661 Fan Loop Functional Diagram

COMMAND READ LIMIT/FAILURE REGISTER

Label

(MSB)

Data Bit

POR State 1 1 1 1 1 1 1 1

Table 11. Fan Tachometer Period Limit (RFTCL/WWFTCL)

Note: The fan tachometer period limit register is programmed with the maximum speed that is compared against the value in the FS

1 2 ... 12 13 14 15 16 17 18 19

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Rainbow-electronics MAX6661 Manual de usuario Pagina 17

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