MAX6639FAEE+T Maxim Integrated Products, MAX6639FAEE+T Datasheet - Page 8

• Manufacturer Part Number: MAX6639FAEE+T
• Description: IC 2CH TEMP MONITOR 16-QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6639FAEE+T

• Function: Fan Control, Temp Monitor
• Topology: ADC, PWM Generator, Tach Counter
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 150°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
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 tempera-
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
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.
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.
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 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
Table 2. Temperature Data Byte Format
8
_______________________________________________________________________________________
TEMP (°C)
1.50
0.00
241
240
126
25
TEMP (°C)
+241
+240
+126
+25
1
0
DIGITAL OUTPUT
1111 0001
1111 0000
0111 1110
0001 1001
0000 0001
0000 0000
OT Output
THERM
when bit 6 in address 13h (fan 1) or bit 6 in address
17h (fan 2) is set.
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.
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.
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
Table 3. Tachometer Setting
FAN RPM
RANGE
16,000
2000
4000
8000
TACH1 and TACH2 Inputs
INTERNAL CLOCK
FREQUENCY (kHz)
1
2
4
8
FANFAIL
ALERT