MAX6651EEE datasheet(11/25 Pages) MAXIM

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Alarm Status Register if the condition that caused the

alarm is removed.

Tachometer

The Tachometer Count Registers record the number of

pulses on the corresponding tachometer input during the

period defined by the Tachometer Count-Time Register.

The MAX6651 contains three additional tachometer

inputs, which may be used to monitor additional fans. For

accurate control of multiple fans, use identical fans.

The Tachometer Count-Time Register sets the integration

time over which the MAX6650/MAX6651 count tachome-

ter pulses. The devices can count up to 255 (FFh) pulses

during the selected count time. If more than 255 pulses

occur, the IC sets the overflow alarm and the Tachometer

Count Register reports the maximum value of 255. Set

the time register so the count register will not overflow

under worst-case conditions (maximum fan speed) while

maximizing resolution. Calculate the maximum measur-

able fan speed and minimum resolution with the following

equations:

Max Fan Speed (in RPS) = 255 / (2 x tCOUNT)

Min Resolution (in RPS) = 1 / (2 x tCOUNT)

where tCOUNT is the tachometer count time; 1kHz is the

maximum allowable tachometer input frequency for the

MAX6650/MAX6651.

Fan-Speed Regulators and Monitors

with SMBus/I2C-Compatible Interface

Maxim Integrated

MAX6650/MAX6651

Table 5. GPIO Definition Register

Table 6. GPIO Status Register

BIT

POR

(DEFAULT)

STATE

MAX6650

MAX6651

STATE

FUNCTION

GPIO4 outputs a logic-low level.

N/A

(must be 1)

GPIO4

GPIO4 outputs a logic-high level or serves as an input.

GPIO3 outputs a logic-low level.

N/A

(must be 1)

GPIO3

GPIO3 outputs a logic-high level or serves as an input.

GPIO2 serves as an external clock input.

GPIO2 serves as an internal clock output.

GPIO2 outputs a logic-low level.

5:4

N/A

(must be 11)

GPIO2

GPIO2 outputs a logic-high level or serves as an input.

GPIO1 outputs a logic-high level or serves as an input.

GPIO1 serves as a

FULL ON input.

GPIO1 outputs a logic-low level.

3:2

GPIO1

GPIO1 outputs a logic-high level or serves as an input.

GPIO0 outputs a logic-high level or serves as an input.

GPIO0 serves as an

ALERT output.

GPIO0 outputs a logic-low level.

1:0

GPIO0

GPIO0 outputs a logic-high level or serves as an input.

BIT

NAME

POR

(DEFAULT

STATE)

7 (MSB) to 5

Always 0

GPIO4 (MAX6651 only)

GPIO3 (MAX6651 only)

GPIO2 (MAX6651 only)

1GPIO1

0 (LSB)

GPIO0

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