MAX6641AUB96+ Maxim Integrated Products, MAX6641AUB96+ Datasheet - Page 13

• Manufacturer Part Number: MAX6641AUB96+
• Description: IC TEMP MONITOR SMBUS 10UMAX
• Manufacturer: Maxim Integrated Products

Specifications of MAX6641AUB96+

• Function: Fan Control, Temp Monitor
• Topology: ADC, PWM Generator, Tach Counter
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Full Temp Accuracy: +/- 4 C
• Digital Output - Bus Interface: Serial (2-Wire)
• Digital Output - Number Of Bits: 8 bit
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The frequency-select register controls the frequency of
the PWM signal. When the PWM signal modulates the
power supply of the fan, a low PWM frequency (usually
33Hz) should be used to ensure the circuitry of the
brushless DC motor has enough time to operate. When
driving a fan with a PWM-to-DC circuit, as in Figure 6,
the highest available frequency (35kHz) should be
used to minimize the size of the filter capacitors. When
using a fan with a PWM control input, the frequency
should normally be high as well, although some fans
have PWM inputs that accept low-frequency drive.
The duty cycle of the PWM can be controlled in two ways:
1) Manual PWM control by setting the duty cycle of
2) Automatic PWM control by setting the duty cycle
Setting bits D5 and D4 to zero in the fan-configuration
register (0Dh) enables manual PWMOUT control. In this
mode, the duty cycle written to the fan-target duty-
cycle register controls the PWMOUT duty cycle. The
value is clipped to a maximum of 240, which corre-
sponds to a 100% duty cycle. Any value above that is
limited to the maximum duty cycle. In manual control
mode, the value of the maximum duty-cycle register is
ignored and does not affect the duty cycle.
In the automatic control mode, the duty cycle is con-
trolled by the local or remote temperature, according to
the settings in the control registers. Below the value of
the fan-start temperature threshold (set by registers 03h
and 04h), the duty cycle is equal to the fan-start duty
cycle. Above the fan-start temperature, the duty cycle
increases by one duty-cycle step each time the tempera-
ture increases by one temperature step. Below the fan-
start temperature, the duty cycle is either 0% or it is
equal to the fan-start duty cycle, depending on the value
of bit D3 in the configuration byte register. See Figure 8.
The target duty cycle is calculated based on the follow-
ing formula:
For temperature > fan-start temperature:
where:
DC = DutyCycle
the fan directly through the fan-target duty-cycle
register (09h).
based on temperature.
SMBus-Compatible Temperature Monitor with
DC
FSDC
Automatic PWM Duty-Cycle Control
______________________________________________________________________________________
Manual PWM Duty-Cycle Control
Automatic PWM Fan-Speed Controller
(
T
-
FST
)
DCSS
TS
FSDC = FanStartDutyCycle
T = Temperature
FST = FanStartTemperature
DCSS = DutyCycleStepSize
TS = TempStep
Duty cycle is recalculated after each temperature con-
version if temperature is increasing. If the temperature
begins to decrease, the duty cycle is not recalculated
until the temperature drops by 5 C from the last peak
temperature. The duty cycle remains the same until the
temperature drops 5 C from the last peak temperature
or the temperature rises above the last peak tempera-
ture. For example, if temperature goes up to +85 C and
starts decreasing, duty cycle is not recalculated until
the temperature reaches +80 C or the temperature
rises above +85 C. If temperature decreases further,
the duty cycle is not updated until it reaches +75 C.
For temperature < fan-start temperature and bit D3 of
the configuration byte register = 0:
For temperature < fan-start temperature and bit D3 of
the configuration byte register = 1:
Once the temperature crosses the fan-start tempera-
ture threshold, the temperature has to drop below the
fan-start temperature threshold minus the hysteresis
before the duty cycle returns to either 0% or fan-start
duty cycle. The value of the hysteresis is set by D7 of
the fan-configuration register.
Figure 8. Automatic PWM Duty Control
DUTY CYCLE
FAN START
DUTY CYCLE
Dutycycle = FanStartDutyCycle
REGISTER 02H,
BIT D3 = 1
TEMPERATURE
DutyCycle = 0
FAN START
REGISTER 02H,
BIT D3 = 0
TEMP
STEP
TEMPERATURE
DUTY CYCLE
STEP SIZE
13