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MAX6640 Datasheet(PDF) 10 Page - Maxim Integrated Products

Part No. MAX6640
Description  2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com
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MAX6640 Datasheet(HTML) 10 Page - Maxim Integrated Products

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TMIN. If bit 0 is equal to zero, the fan will be 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 MAX6640 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.
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.
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 MAX6640 into low-power sleep mode.
• D6: Software POR. Writing a 1 resets all registers to
their default values.
2-Channel Temperature Monitor with Dual
Automatic PWM Fan-Speed Controller
10
______________________________________________________________________________________
TACHMAX
TACH
0xFFh
TACHMIN
TEMPERATURE
TB
TMIN-5
TMIN
TACHB+1
TACHA+1
Figure 4. Tachometer Target Calculation
RPM
0
RPMMAX
RPMMIN
TEMPERATURE
TMIN-5
TMIN
TB
TACHA+1
TACHB+1
Figure 5. RPM Target Calculation


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