MAX6639AEE+ Datasheet MAX6639ATE+T, MAX6639EVKIT+, MAX6639FATE+ | P13-P15

Mask Register (03h)

This register masks the ALERT, OT, THERM, and

FANFAIL outputs. A 1 prevents the corresponding fail-

ures from being asserted on these outputs. The mask

bits do not affect the status register.

Global Configuration Register (04h)

The global configuration register controls the shutdown

mode, power-on reset, SMBus timeout, and tempera-

ture channel 2 source select:

• D7: Run/Standby. Normal operation is run (0).

Setting this bit to 1 suspends conversions and puts

the MAX6639 into low-power sleep mode.

• D6: Software POR. Writing a 1 resets all registers to

their default values.

• D5: SMBus Timeout Disable. Writing a zero enables

SMBus timeout for prevention of bus lockup. When

the timeout function is enabled, the SMBus interface

is reset if SDA or SCL remains low for more than

74ms (typ).

• D4: Temperature Channel 2 Source. Selects either

local or remote 2 as the source for temperature chan-

nel 2 register data. Writing a zero to this bit selects

remote 2 for temperature channel 2.

• D3: PWM Output Frequency Range. Selects either

the 20Hz to 100Hz range or the 5kHz to 25kHz range

for the PWM outputs (see Table 9).

Extended Temperature Registers (05h and 06h)

These registers contain the extended temperature data

from channels 1 and 2. Bits D[7:5] contain the 3 LSBs

of the temperature data. The bit values are 0.5°C,

0.25°C, and 0.125°C. When bit 0 is set to 1, a diode

fault has been detected.

Channel 1 and Channel 2 ALERT, OT, and THERM

Limits (08h Through 0Dh)

These registers contain the temperatures above which

the ALERT, THERM, and OT status bits set and outputs

assert (for the temperature channels that are not

masked). The data format is the same as that of the

channel 1 and channel 2 temperature registers: the

LSB weight is +1°C and the MSB is +128°C.

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

Maxim Integrated 13

MAX6639/MAX6639F

READ/

WRITE

NO.

ADDRESS

POR

STATE

FUNCTION D7 D6 D5 D4 D3 D2 D1 D 0

W 26h

0011

1100

Fan 1 target

duty cycle

MSB——————LS B

R 27h

0000

Fan 2 current

duty cycle

MSB——————LS B

W 27h

0011

1100

Fan 2 target

duty cycle

MSB——————LS B

R/W 28h

0100

000

Channel 1

minimum

fan-start

temperature

MSB——————LS B

R/W 29h

0100

0000

Channel 2

minimum

fan-start

temperature

MSB——————LS B

R 3Dh

0101

1000

Read device

01011000

R 3Eh

0100

1101

Read

manufacturer

01001101

R 3Fh

0000

Read device

revision

00000000

Table 4. Register Map (continued)

Fan 1 and 2 Configuration 1 (10h and 14h)

The following registers control the modes of operation

of the MAX6639:

• D7: PWM Mode. D7 = 1 sets the fan into manual

PWM duty-cycle control mode. Write the target duty

cycle in the fan duty-cycle register. D7 = 0 puts the

fan into RPM control mode. To set RPM manually, set

both fan-control temperature channels (bits D2 and

D3) to zero and write the desired tachometer count

into the TACH count register.

• D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4]

sets the time between increments of the duty cycle.

Each increment is 1/120 of the duty cycle. By adjust-

ing the rate-of-change, audibility of fan-speed

changes can be traded for response time. Table 5

shows the effect of D[6:4] and, for reference, the time

required for the fan speed to change from 33% to

100% duty cycle as a function of the rate-of-change

bits.

• D[3:2]: Temperature Channel(s) for Fan Control.

Selects the temperature channel(s) that control the

PWM output when the MAX6639 is in automatic RPM

control mode (PWM mode bit is zero). If two chan-

nels are selected, the fan goes to the higher of the

two possible speeds. If neither channel is selected,

then the fan is in manual RPM mode and the speed

is forced to the value written to the target tach count

• D[1:0]: RPM Range. Scales the tachometer counter

by setting the maximum (full-scale) value of the RPM

range to 2000, 4000, 8000, or 16,000. (Table 3

shows the internal clock frequency as a function of

the range.)

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

14 Maxim Integrated

MAX6639/MAX6639F

A C T U A L R A T E O F CH A N G E AT SPEC IF I C PW M FREQUENCIES

OR 14h D[6:4]

NOMINAL RATE

OF CHANGE (s)

100Hz (s) 50Hz (s) 33.3Hz (s) 20Hz (s)

NOMINAL TIME FROM

33% TO 100% (s)

000 0 0000 0

001 0.0625 0.06 0.06 0.06 0.05 5

010 0.125 0.13 0.12 0.12 0.15 10

011 0.25 0.25 0.26 0.24 0.25 20

100 0.5 0.5 0.5 0.51 0.5 40

101 1 1 1 0.99 1 80

110 2 2 2 1.98 2 160

111 4 4 4 3.96 4 320

Table 5. Fan Duty-Cycle Rate-of-Change

00 2000

01 4000

10 8000

11 16,000

Table 6. Fan RPM Speed

MAXIMUM RPM VALUE ACTUAL RPM

SELECTED NUMBER

OF PULSES PER

REVOLUTION

ACTUAL FAN PULSES

PER REVOLUTION

TACHOMETER COUNT

VALUE*

2000 1000 2 2 3Ch

4000 1000 2 2 78h

4000 3000 2 2 28h

4000 3000 2 4 14h

16,000 8000 4 4 3Ch

16,000 8000 4 2 78h

Table 7. RPM-to-Tachometer Count Relationship Examples

Tachometer count value = ((internal clock frequency) x 60) / actual RPM) (selected number of pulses per revolution / actual fan pulses)

Fan 1 and 2 Configuration 2a (11h and 15h)

The following registers apply to the automatic RPM con-

trol mode:

• D[7:4]: Fan RPM (Tachometer) Step-Size A.

Selects the number of tachometer counts the target

value decreases for each temperature step increase

above the fan-start temperature. Value = n + 1 (1

through 16) where n is the value of D[7:4].

• D[3:2]: Temperature Step Size. Selects the temper-

ature increment for fan control. For each temperature

step increase, the target tachometer count decreas-

es by the value selected by D[7:4] (Table 8).

• D1: PWM Output Polarity. PWM output is low at

100% duty cycle when this bit is set to zero. PWM

output is high at 100% duty cycle when this bit is set

to 1.

• D0: Minimum Speed. Selects the value of the mini-

mum fan speed (when temperature is below the fan-

start temperature in the automatic RPM control

mode). Set to zero for 0% fan drive. Set to 1 to deter-

mine the minimum fan speed by the tachometer

count value in registers 22h and 23h (fan maximum

TACH).

Fan 1 and 2 Configuration 2b (12h and 16h)

The following registers select the tachometer step sizes

and number of steps for step-size A to step-size B

slope changes (see Figure 1):

• D[7:4]: RPM (Tachometer) Step Size B. Selects

number of tachometer counts the target value

decreases for each temperature step increase after

the number of steps selected by D[3:0]. Value = n +

1 (1 through 16) where n is the value of D[7:4].

• D[3:0]: Selects the number of temperature/tachome-

ter steps above the fan-start temperature at which

step-size B begins.

Fan 1 and Fan 2 Configuration 3 (13h and 17h)

The following registers control fan spin-up, PWM output

frequency, pulse stretching, and THERM to fan full-

speed enable:

• D7: Fan Spin-Up Disable. Set to zero to enable fan

spin-up. Whenever the fan starts up from zero drive,

it is driven with 100% duty cycle for 2s to ensure that

it starts. Set to 1 to disable the spin-up function.

• D6: THERM to Full-Speed Enable. When this bit is

1, THERM going low (either by being pulled low

externally or by the measured temperature exceed-

ing the THERM limit) forces the fan to full speed. In

all modes, this happens at the rate determined by

the rate-of-change selection. When THERM is

deasserted (even if the fan has not reached full

speed), the speed falls at the selected rate-of-

change to the target speed.

• D5: Disable Pulse Stretching. Pulse stretching is

enabled when this bit is set to zero. When modulat-

ing the fan’s power supply with the PWM signal, the

PWM pulses are periodically stretched to keep the

tachometer signal available for one full revolution.

Setting this bit to 1 disables pulse stretching. The

MAX6639 still measures the fan speed but does not

stretch the pulses for measurements, so the fan’s

power supply must not be pulse modulated.

• D[1:0]: PWM Output Frequency. These bits control

the PWM output frequency as shown in Table 9.

Fan Tach Count 1 and 2 (20h and 21h)

These registers have the latest tachometer measure-

ment of the corresponding channel. This is inversely

proportional to the fan’s speed. The fan RPM range

should be set so this count falls in the 30 to 160 range

for normal fan operation.

Fan Start Tach Count/Target Tach Count

(22h and 23h)

D[7:0]: This sets the starting tachometer count for the

fan in automatic RPM mode. Depending on the setting

of the minimum duty-cycle bit, the tachometer count

has this value either at all temperatures below the fan-

start temperature or the count is zero below the fan-

start temperature and has this value when the fan-start

temperature is reached. These registers are the target

tach count when in manual RPM mode.

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

Maxim Integrated 15

MAX6639/MAX6639F

OR 15h

FAN CONTROL TEMPERATURE

STEP SIZE (°C)

00 1

01 2

10 4

11 8

Table 8. Temperature Step Size

REGISTERS

13h AND 16h

LOW-FREQUENCY

(Hz) REGISTER

04h D3 = 0

HIGH-FREQUENCY

(kHz) REGISTER

04h D3 = 1

20 5

33.33 8.33

50 12.5

100 25

Table 9. Fan PWM Frequency

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P22

MAX6639AEE+

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