Fan-Start Temperature

The minimum fan-start temperature register contains

the temperature at which fan control begins. Note: This

applies only to automatic RPM mode. Refer to the

MAX6639 IC data sheet for more information on auto-

matic RPM mode operation.

Read the minimum fan-start temperature by pressing

the Read button (Figure 1). The value (in Celsius) is

shown to the right of the button. Change the minimum

fan-start temperature by entering the values (in Celsius)

into the edit boxes and pressing the Write buttons.

Global Configuration

The global configuration register has several functions.

Figure 2 displays the checkboxes that configure the

register. Each checkbox corresponds to a bit in the

register. Table 2 describes the function of each check-

box. Read the global configuration register by pressing

the Read button. Change the global configuration reg-

ister by checking or unchecking the desired function

checkbox and pressing the Write button.

Mask

The mask register enables or disables the

ALERT, OT,

THERM, or FANFAIL outputs. Figure 3 displays the

checkboxes that configure the register. Each checkbox

corresponds to a bit in the register. Table 3 describes

the function of each checkbox. Read the mask register

by pressing the Read button. Change the mask by

selecting or deselecting the desired masks and press-

ing the Write button.

Status

The Status (0x02) group box displays the critical and

fault conditions that occur. Each line corresponds to a

bit in the registers. See Table 4 for a list of the status

conditions.

Read the status by pressing the Read Status button

within the Status (0x02) group box.

Fan 1 and Fan 2 Configuration 1

The fan 1 Configuration 1 (0x10) and fan 2

Configuration 1 (0x14) group boxes control the modes

of operation of the fans (Figure 4). The Configuration 1

(0x14) group box is not shown, but can be accessed

by navigating to the Fan 2 tab sheet from Figure 4.

These group boxes contain four items: Mode, Rate of

Change, Control, and RPM Range.

The Mode drop-down list has two options: PWM mode

or RPM mode. Select PWM mode to control the PWM

duty cycle manually. RPM mode allows for either man-

ual or automatic control of the fan’s RPM.

The Rate of Change drop-down list sets the time

between adjustments of the duty cycle. Each adjust-

ment is 1/120 of the PWM period. By adjusting the Rate

MAX6639 Evaluation Kit

6

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Table 2. Global Configuration Register Checkboxes

BIT

NAME

STATE

DESCRIPTION

Checked

Places the MAX6639 in software standby mode

7

STOP

Unchecked*

Places the MAX6639 in operational mode

Checked

Resets all registers to their default values, including the global configuration

register. After selecting the POR checkbox, the checkbox returns to the

unchecked state.

6

POR

Unchecked*

Normal operation

Checked*

Enables the SMBus timeout

5

SMB Timeout

Enabled

Unchecked

Disables the SMBus timeout, as well as the alert response, thus providing true

Checked*

The local sensor on the MAX6639 is the source for channel 2

4

Channel 2

Source = Local

Unchecked

The remote sensor connected to DXP2 and DXN is the source for channel 2

Checked

Enables high-frequency PWM output on the MAX6639

3

High-Freq Enabled

(MAX6639 only)

Unchecked*

Enables low-frequency PWM output

2

Reserved

N/A

Not used

1

Reserved

N/A

Not used

0

Reserved

N/A

Not used

*

Power-on-reset (POR) state.