MAX6651 View Datasheet(PDF) - Maxim Integrated

Part Name

Description

Manufacturer

MAX6651

Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface

Maxim Integrated 

MAX6650/MAX6651

Fan-Speed Regulators and Monitors

with SMBus/I2C-Compatible Interface

Table 2. Command-Byte Assignments

REGISTER

SPEED

CONFIG

GPIO DEF

DAC

ALARM ENABLE

ALARM

TACH0

TACH1

TACH2

TACH3

GPIO STAT

COUNT

COMMAND

0000 0000

0000 0010

0000 0100

0000 0110

0000 1000

0000 1010

0000 1100

0000 1110

0001 0000

0001 0010

0001 0100

0001 0110

READ

x

x

x

x

x

x

x

x

x

x

x

x

WRITE

x

x

x

x

x

—

—

—

—

—

—

x

POR (DEFAULT)

STATE

00h

0Ah

FFh

00h

00h

00h

00h

00h

00h

00h

1Fh

02h

FUNCTION

Fan speed

Configuration

GPIO definition

DAC

Alarm enable

Alarm status

Tachometer 0 count

Tachometer 1 count

Tachometer 2 count

Tachometer 3 count

GPIO status

Tachometer count time

Table 3. Fan Speed

KTACH

tTACH

KSCALE (ms)

1

4

16

0000 0000

1.0

*

*

0000 0001

1.0

*

*

0000 0010

1.5

*

*

—

—

—

—

0001 1110

16

3.9

*

0001 1111

16

4.0

1.0

0010 0000

17

4.2

1.0

—

—

—

—

0100 0000

33

8.2

2.1

—

—

—

—

1111 1000

125

31

7.8

*The minimum allowed tachometer period is 1ms.

FAN SPEED (RPS)

KSCALE

1

4

16

500

*

*

500

*

*

330

*

*

—

—

—

32

128

*

31

124

500

30

120

480

—

—

—

15.3

61.1

240

—

—

—

4

15.9

64

FAN SPEED (RPM)

KSCALE

1

4

16

30,000

*

*

30,000

*

*

20,000

*

*

—

—

—

1900

7700

*

1900

7400 30,000

1800

7200 29,000

—

—

—

910

3700 15,000

—

—

—

240

960

3830

tor that overrides the internal oscillator (see General-

Purpose Input/Output). When using an external oscillator

(fOSC), calculate the Fan-Speed Register value with fCLK

equal to fOSC. Codes above F8h (1111 1000) are

allowed, but will not significantly decrease the frequency.

Configuration-Byte Register

The Configuration-Byte Register (Table 4) adjusts the

prescaler, changes the tachometer threshold voltage,

and sets the mode of operation. The three least-signifi-

cant bits configure the prescaler division used to scale

the tachometer period. Select the prescaler value so the

fan’s full speed is achieved with a register value of

approximately 64 (0100 0000) to optimize speed range

and resolution (see the Fan Speed Register section). The

fourth bit selects the fan operating voltage.

The fifth and sixth bits configure the operating mode.

The MAX6650/MAX6651 have four modes of operation:

full-on, full-off (shutdown), closed-loop, and open-loop.

In closed-loop operation, the external microcontroller

(µC) sets the desired speed by writing an 8-bit word to

the Fan-Speed Register (see the Fan-Speed Register

section). The MAX6650/MAX6651 monitor the fan’s

tachometer output and automatically adjust the voltage

Maxim Integrated

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