MAX6639AEE+ Datasheet MAX6639ATE+T, MAX6639EVKIT+, MAX6639FATE+ | P7-P9

SMBus Digital Interface

From a software perspective, the MAX6639 appears as

a set of byte-wide registers. This device uses a stan-

dard SMBus 2-wire/I

C-compatible serial interface to

access the internal registers.

The MAX6639 features an address select input (ADD)

that allows the MAX6639 to have three unique addresses

(see Table 1).

The MAX6639 employs four standard SMBus protocols:

write byte, read byte, send byte, and receive byte

(Figures 1, 2, and 3). The shorter receive byte protocol

allows quicker transfers, provided that the correct data

tion. Use caution with the shorter protocols in multimas-

ter systems, since a second master could overwrite the

command byte without informing the first master.

Table 4 details the register addresses and functions,

whether they can be read or written to, and the power-

on reset (POR) state. See Tables 5–9 for all other regis-

ter functions and the

section.

Temperature Reading

Temperature data can be read from registers 00h and

01h. The temperature data format for these registers is

8 bits, with the LSB representing 1°C (Table 2) and the

MSB representing +128°C. The MSB is transmitted first.

Three additional temperature bits provide resolution

down to 0.125°C and are in the channel 1 extended

temperature (05h) and channel 2 extended temperature

(06h) registers. All values below 0°C clip to 00h.

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

Maxim Integrated 7

MAX6639/MAX6639F

SCL

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

AB CD

HIJ

SDA

SU:STA

HD:STA

LOW

HIGH

SU:DAT

SU:STO

BUF

LMK

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

Figure 2. SMBus Write Timing Diagram

SCL

AB CD

FG H

SDA

SU:STA

HD:STA

LOW

HIGH

SU:DAT

HD:DAT

SU:STO

BUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = MASTER PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO SLAVE

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

Figure 3. SMBus Read Timing Diagram

ADD INPUT STATE I

C SLAVE ADDRESS

BINARY

EQUIVALENT

5Eh 0101 111

Floating 5Ch 0101 110

GND 58h 0101 100

Table 1. I

C Slave Address

The MAX6639 employs a register lock mechanism to

avoid getting temperature results from the temperature

pled at two different time points. Reading the extended

ture register for at least 0.25s, unless there is a temper-

ature register read before the scheduled update. This

allows enough time to read the main register before it is

updated, thereby preventing reading the temperature

temperature register data from a different conversion.

The MAX6639 measures the temperature at a fixed rate

of 4Hz immediately after it is powered on. Setting bit 7

of the configuration register (04h) shuts down the tem-

perature measurement cycle.

Output

When a measured temperature exceeds the corre-

sponding OT temperature threshold and OT is not

masked, the associated OT status register bit sets and

the OT output asserts. If OT for the respective channel

is masked, the OT status register sets, but the OT out-

put does not assert. To deassert the OT output and the

associated status register bit, either the measured tem-

perature must fall at least 5°C below the trip threshold

or the trip threshold must be increased to at least 5°C

above the current measured temperature.

THERM

When a measured temperature exceeds the corre-

sponding THERM temperature threshold and THERM is

not masked, the associated THERM status register bit

is set and the THERM output asserts. If THERM for the

respective channel is masked, the THERM status regis-

ter is set, but the THERM output does not assert. To

deassert the THERM output and the associated status

at least 5°C below the trip threshold or the trip threshold

must be increased to at least 5°C above the current

measured temperature. Asserting THERM internally or

externally forces both PWM outputs to 100% duty cycle

when bit 6 in address 13h (fan 1) or bit 6 in address

17h (fan 2) is set.

ALERT

The ALERT output asserts to indicate that a measured

temperature exceeds the ALERT trip threshold for that

temperature channel. The status bit and the ALERT out-

put clear by reading the ALERT status register. If the

ALERT status bit is cleared, but the temperature still

exceeds the ALERT temperature threshold, ALERT

reasserts on the next conversion, and the status bit sets

again. A successful alert response protocol clears

ALERT but does not affect the ALERT status bit.

TACH1 and TACH2 Inputs

To measure the fan speed, the MAX6639 has two

tachometers. Each tachometer has an accurate internal

clock to count the time elapsed in one revolution.

Therefore, it is counting the time between two tachome-

ter pulses for a fan with four poles. When the PWM sig-

nal is used to directly modulate the fan’s power supply,

the PWM frequency is normally in the 20Hz to 100Hz

range. In this case, the time required for one revolution

may be longer than the PWM on-time. For this reason,

the PWM pulses are periodically stretched to allow

tachometer measurement over a full revolution. Turn off

pulse stretching by setting bit 5 of register 13h or regis-

ter 17h when using a 4-wire fan.

The tachometer count is inversely proportional to the

fan’s RPM. The tachometer count data is stored in regis-

ter 20h (for TACH1) and register 21h (for TACH2).

Reading a value of 255 from the TACH count register

means the fan’s RPM is zero or too slow for the range.

Reading a value of zero in the TACH count register

means the fan’s RPM is higher than the range selected.

Table 2 shows the fan’s available RPM ranges. Use reg-

isters 10h or 14h to select the appropriate RPM range for

the fan being used.

FANFAIL

The FANFAIL output asserts to indicate that one of the

fans has failed or is spinning slower than the required

speed. The MAX6639 detects fan fault depending on the

fan-control mode. In PWM mode, the MAX6639 pro-

duces a square wave with a duty cycle set by the value

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

8 Maxim Integrated

MAX6639/MAX6639F

TEMP (°C) TEMP (°C) DIGITAL OUTPUT

241 +241 1111 0001

240 +240 1111 0000

126 +126 0111 1110

25 +25 0001 1001

1.50 1 0000 0001

0.00 0 0000 0000

Table 2. Temperature Data Byte Format

FAN RPM

RANGE

INTERNAL CLOCK

FREQUENCY (kHz)

2000 1

4000 2

8000 4

16,000 8

Table 3. Tachometer Setting

written to the duty-cycle registers (26h and 27h). In this

mode, the MAX6639 signals a fan fault when the

tachometer count is greater than the maximum tachome-

ter count value stored in the appropriate register (22h

and 23h). After the MAX6639 asserts FANFAIL, the fan

with a tachometer fault goes to full speed for 2s in an

attempt to restart the fan and then returns to the original

duty-cycle settings. Reading the status register clears

the FANFAIL status bits and the output. The MAX6639

measures the fan speed again after 2s. The MAX6639

asserts FANFAIL if it detects the fan fault again.

In RPM mode (either automatic or manual), the

MAX6639 checks for fan failure only when the duty

cycle reaches 100%. It asserts FANFAIL when the

tachometer count is greater than twice the target

tachometer count. In manual RPM mode, registers 22h

and 23h store the target tachometer count value. In

automatic RPM mode, these registers store the maxi-

mum tachometer count.

Fan-Speed Control

The MAX6639 adjusts fan speed by controlling the duty

cycle of a PWM signal. This PWM signal then either

modulates the DC brushless fan’s power supply or dri-

ves a speed-control input on a fan that is equipped with

one. There are three speed-control modes: PWM, in

which the PWM duty cycle is directly programmed over

the SMBus; manual RPM, in which the desired

tachometer count is programmed into a register and

the MAX6639 adjusts its duty cycle to achieve the

desired tachometer count; and automatic RPM, in

which the tachometer count is adjusted based on a

programmed temperature profile.

The MAX6639 divides each PWM cycle into 120 time

slots. Registers 26h and 27h contain the current values

of the duty cycles for PWM1 and PWM2, expressed as

the effective time-slot length. For example, the PWM1

output duty cycle is 25% when register 26h reads 1Eh

(30/120).

PWM Control Mode

Enter PWM mode by setting bit 7 of the fan 1 or 2 con-

figuration 1 register (10h and 14h) to 1. In PWM control

mode, the MAX6639 generates PWM signals whose

duty cycles are specified by writing the desired values

to fan duty-cycle registers 26h and 27h. When a new

duty-cycle value is written into one of the fan duty-cycle

registers, the duty cycle changes to the new value at a

rate determined by the rate-of-change bits [6:4] in the

fan 1 or 2 configuration 1 register. The rate-of-change

of the duty cycle ranges from 000 (immediately

changes to the new programmed value) to 111

(changes by 1/120 every 4s). See Table 5 and the

Fan

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

section.

Manual RPM Control Mode

Enter manual RPM control mode by setting bits 2, 3,

and 7 of the fan 1 or 2 configuration 1 register (10h and

14h) to zero. In the manual RPM control mode, the

MAX6639 adjusts the duty cycle and measures the fan

speed. Enter the target tachometer count in register

22h for fan 1 and register 23h for fan 2. The MAX6639

compares the target tachometer count with the mea-

sured tachometer count and adjusts the duty cycle so

that the fan speed gradually approaches the target

tachometer count.

The first time manual RPM control mode is entered, the

initial PWM duty cycle is determined by the target

tachometer count:

where targetTACH is the value of the target tachometer

count in the target tach count register (22h or 23h).

If the initial duty-cycle value is over 120, the duty cycle

is 100%. If spin-up is enabled (bit 7 in registers 13h

and 17h) and the fan is not already spinning, the duty

cycle first goes to 100% and then goes to the initial

duty-cycle value. Every 2s, the MAX6639 counts the

fan’s period by counting the number of pulses stored in

registers 24h and 25h. If the count is different from the

target count, the duty cycle is adjusted.

If a nonzero rate-of-change is selected, the duty cycle

changes at the specified rate until the tachometer count

is within ±5 of the target. Then the MAX6639 gets into a

locked state and updates the duty cycle every 2s.

Automatic RPM Control Mode

In the automatic RPM control mode, the MAX6639 mea-

sures temperature, sets a target tachometer count

based on the measured temperature, and then adjusts

the duty cycle so the fan spins at the desired speed.

Enter this mode by setting bit 7 of the fan 1 or 2 config-

uration 1 register (10h and 14h) to zero and selecting

the temperature channel that controls the fan speed

using bits 2 and 3 of the configuration register.

In both RPM modes (automatic and manual), the

MAX6639 implements a low limit for the tachometer

counts. This limits the maximum speed of the fan by

ensuring that the fan’s tachometer count does not go

lower than the tachometer count specified by bits 5

through 0 of register 24h for fan 1 and register 25h for

fan 2. Typical values for the minimum tachometer count

Initial duty cycle

t etTACH

arg

−255

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

Maxim Integrated 9

MAX6639/MAX6639F

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

MAX6639AEE+

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Board Mount Temperature Sensors 2Ch Temperature Monito

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