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MAX6639 Datasheet(PDF) 8 Page - Maxim Integrated Products

Part No. MAX6639
Description  2-Channel Temperature Monitor with Dual, Automatic, PWM Fan-Speed Controller
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Manufacturer  MAXIM [Maxim Integrated Products]
Direct Link  https://www.maximintegrated.com/en.html
Logo MAXIM - Maxim Integrated Products

MAX6639 Datasheet(HTML) 8 Page - Maxim Integrated Products

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Three additional temperature bits provide resolution
down to 0.125
°C and are in the channel 1 extended
temperature (05h) and channel 2 extended tempera-
ture (06h) registers. All values below 0°C clip to 00h.
The MAX6639 employs a register lock mechanism to
avoid getting temperature results from the temperature
register and the extended temperature register sam-
pled at two different time points. Reading the extended
register stops the MAX6639 from updating the temper-
ature register for at least 0.25s, unless there is a tem-
perature register read before the scheduled update.
This allows enough time to read the main register
before it is updated, thereby preventing reading the
temperature register data from one conversion and the
extended 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.
OT 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
register bit, either the measured temperature must fall
at least 5
°C below the trip threshold or the trip thresh-
old 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.
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
8
_______________________________________________________________________________________
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


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