MAX6639(2005) Просмотр технического описания (PDF) - Maxim Integrated

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MAX6639
(Rev.:2005)

2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller

Maxim Integrated 

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

TACH

0xFFh

TMIN-5 TMIN

TACHMAX

TACHA+1

TB

TEMPERATURE

RPM

RPMMAX

TACHB+1

TACHA+1

TACHMIN

TACHB+1

Figure 4. Tachometer Target Calculation

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

are 30h to 60h. Set the value to correspond to the full-

rated RPM of the fan. See Figure 4.

Figure 5 shows how the MAX6639 calculates the target

tachometer value based on the measured temperature.

At TMIN, the fan spins at a minimum speed value corre-

sponding to the maximum tachometer count value

stored in register 22h or 23h. Bit 0 of register 11h (fan

1) and register 15h (fan 2) selects the behavior below

TMIN. If bit 0 is equal to zero, the fan is completely off

below TMIN. When the temperature is falling, it must

drop 5°C below TMIN before the fan turns off. If bit 0 is

set to 1, the fan does not turn off below TMIN, but

instead stays at the maximum tachometer count in reg-

ister 22h or 23h.

When the measured temperature is higher than TMIN,

the MAX6639 calculates the target tachometer count

value based on two linear equations. The target

tachometer count decreases by the tach step size

value stored in bits 7 through 4 of registers 11h and

15h each time the measured temperature increases by

the temperature step size value stored in bits 2 and 3 of

registers 11h and 15h. As the measured temperature

continues to increase, a second tachometer step size

goes into effect. Bits 3 through 0 of register 12h and

16h select the number temperature/PWM steps after

which the new step size takes effect. The new step size

is selected by bits 7 to 4 of registers 12h and 16h.

RPMMIN

0

TMIN-5

TMIN

TEMPERATURE

TB

Figure 5. RPM Target Calculation

Register Descriptions

Channel 1 and Channel 2 Temperature Registers

(00h and 01h)

These registers contain the results of temperature mea-

surements. The MSB has a weight of +128°C and the

LSB +1°C. Temperature data for remote diode 1 is in

the channel 1 temperature register. Temperature data

for remote diode 2 or the local sensor (selectable by bit

4 in the global configuration register) is in the channel 2

temperature register. 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. The channel 1

and channel 2 temperature registers do not update

until at least 250ms after the access of the associated

extended temperature registers. All values below 0°C

return 00h.

Status Register (02h)

A 1 indicates that an ALERT, THERM, OT, or fan fault has

occurred. Reading this register clears bits 7, 6, 1, and 0.

Reading the register also clears the ALERT and

FANFAIL outputs, but not the THERM and OT outputs. If

the fault is still present on the next temperature measure-

ment cycle, any cleared bits and outputs are set again.

A successful alert response clears the values on the out-

puts but does not clear the status register bits. The

ALERT bits assert when the measured temperature is

higher than the respective thresholds. The THERM and

OT outputs behave like comparators with 5°C hysteresis.

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.

10 ______________________________________________________________________________________

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