MAX6651 데이터 시트보기 (PDF) - Maxim Integrated

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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 7. Alarm-Enable Register Bit Masks

BIT

NAME

7 (MSB) to 5

4

3

2

1

0 (LSB)

1 = Enabled

—

GPIO2 (MAX6651 only)

GPIO1

TACH

MIN

MAX

POR

(DEFAULT)

STATE

0

0

0

0

0

0

FUNCTION

Always 0

GPIO2 Alarm Enable/Disable (MAX6651 only)

GPIO1 Alarm Enable/Disable

Tachometer Overflow Alarm Enable/Disable

Minimum Output Level Alarm Enable/Disable

Maximum Output Level Alarm Enable/Disable

Table 8. Alarm Status Register Bit Assignments

BIT

NAME

7 (MSB) to 5

4

3

2

1

0 (LSB)

—

GPIO2 (MAX6651 only)

GPIO1

TACH

MIN

MAX

1 = Alarm condition

POR

(DEFAULT)

STATE

0

0

0

0

0

0

FUNCTION

Always 0

GPIO2 Alarm. Set when GPIO2 is low (MAX6651 only).

GPIO1 Alarm. Set when GPIO1 is low.

Tachometer Overflow Alarm

Minimum Output Level Alarm

Maximum Output Level Alarm

Table 9. Tachometer Count-Time Register

(Assumes two pulses per revolution)

REGISTER

VALUE

(KCOUNT)

0000 0000

0000 0001

0000 0010

0000 0011

COUNT

TIME

(s)

0.25

0.5

1.0

2.0

MAXIMUM

FAN SPEED

(RPS)

512

256

128

64

MINIMUM

RESOLUTION

(Hz/COUNT)

2

1

0.5

0.25

The first 6 bits of the Tachometer Count-Time Register

are always zero, and the last 2 bits set the count time

(Table 9). The count time may be determined from the

following equation:

tCOUNT = 0.25s x 2KCOUNT

where KCOUNT is the numerical value of the two 2LSBs.

The 0.25 factor has a ±10% uncertainty.

Upon power-up, the Tachometer Count Registers reset

to 00h and the Tachometer Count-Time Register sets a

1s integration time.

Digital-to-Analog Converter

When using the open-loop mode of operation, the DAC

Register sets the voltage on the low side of the fan. An

internal operational amplifier compares the feedback

voltage (VFB) with the reference voltage set by the 8-bit

DAC, and adjusts the output voltage (VOUT) until the

two input voltages are equal. The voltage at the FB pin

may be determined by the following equation:

VFB = (10 x VREF x KDAC) / 256

and the voltage across the fan is:

VFAN

–

⎛

⎝⎜

90k

10k

+ 1⎞⎠⎟

⎛

⎝⎜

KDAC

256

VREF

⎞

⎠⎟

where KDAC is the numerical value of the DAC Register

and VREF = 1.5V. The minimum feedback voltage is

limited by the voltage drop across the external MOS-

FET (RON x IFAN), and the maximum voltage is limited

by the fan’s supply voltage (VFAN). For linear opera-

12

Maxim Integrated

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