MAX6639FAEE+T Maxim Integrated Products, MAX6639FAEE+T Datasheet - Page 9

• 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

written to the duty-cycle registers (26h and 27h). In this
mode, the MAX6639 signals a fan fault when the
tachometer count is greater than the maximum tachome-
ter count value stored in the appropriate register (22h
and 23h). After the MAX6639 asserts FANFAIL, the fan
with a tachometer fault goes to full speed for 2s in an
attempt to restart the fan and then returns to the original
duty-cycle settings. Reading the status register clears
the FANFAIL status bits and the output. The MAX6639
measures the fan speed again after 2s. The MAX6639
asserts FANFAIL if it detects the fan fault again.
In RPM mode (either automatic or manual), the
MAX6639 checks for fan failure only when the duty
cycle reaches 100%. It asserts FANFAIL when the
tachometer count is greater than twice the target
tachometer count. In manual RPM mode, registers 22h
and 23h store the target tachometer count value. In
automatic RPM mode, these registers store the maxi-
mum tachometer count.
The MAX6639 adjusts fan speed by controlling the duty
cycle of a PWM signal. This PWM signal then either
modulates the DC brushless fan’s power supply or dri-
ves a speed-control input on a fan that is equipped with
one. There are three speed-control modes: PWM, in
which the PWM duty cycle is directly programmed over
the SMBus; manual RPM, in which the desired
tachometer count is programmed into a register and
the MAX6639 adjusts its duty cycle to achieve the
desired tachometer count; and automatic RPM, in
which the tachometer count is adjusted based on a
programmed temperature profile.
The MAX6639 divides each PWM cycle into 120 time
slots. Registers 26h and 27h contain the current values
of the duty cycles for PWM1 and PWM2, expressed as
the effective time-slot length. For example, the PWM1
output duty cycle is 25% when register 26h reads 1Eh
(30/120).
Enter PWM mode by setting bit 7 of the fan 1 or 2 con-
figuration 1 register (10h and 14h) to 1. In PWM control
mode, the MAX6639 generates PWM signals whose
duty cycles are specified by writing the desired values
to fan duty-cycle registers 26h and 27h. When a new
duty-cycle value is written into one of the fan duty-cycle
registers, the duty cycle changes to the new value at a
rate determined by the rate-of-change bits [6:4] in the
fan 1 or 2 configuration 1 register. The rate-of-change
of the duty cycle ranges from 000 (immediately
changes to the new programmed value) to 111
2-Channel Temperature Monitor with Dual,
_______________________________________________________________________________________
Automatic, PWM Fan-Speed Controller
Fan-Speed Control
PWM Control Mode
(changes by 1/120 every 4s). See Table 5 and the Fan
1 and 2 Configuration 1 (10h and 14h) section.
Enter manual RPM control mode by setting bits 2, 3,
and 7 of the fan 1 or 2 configuration 1 register (10h and
14h) to zero. In the manual RPM control mode, the
MAX6639 adjusts the duty cycle and measures the fan
speed. Enter the target tachometer count in register
22h for fan 1 and register 23h for fan 2. The MAX6639
compares the target tachometer count with the mea-
sured tachometer count and adjusts the duty cycle so
that the fan speed gradually approaches the target
tachometer count.
The first time manual RPM control mode is entered, the
initial PWM duty cycle is determined by the target
tachometer count:
where targetTACH is the value of the target tachometer
count in the target tach count register (22h or 23h).
If the initial duty-cycle value is over 120, the duty cycle
is 100%. If spin-up is enabled (bit 7 in registers 13h
and 17h) and the fan is not already spinning, the duty
cycle first goes to 100% and then goes to the initial
duty-cycle value. Every 2s, the MAX6639 counts the
fan’s period by counting the number of pulses stored in
registers 24h and 25h. If the count is different from the
target count, the duty cycle is adjusted.
If a nonzero rate-of-change is selected, the duty cycle
changes at the specified rate until the tachometer count
is within ±5 of the target. Then the MAX6639 gets into a
locked state and updates the duty cycle every 2s.
In the automatic RPM control mode, the MAX6639 mea-
sures temperature, sets a target tachometer count
based on the measured temperature, and then adjusts
the duty cycle so the fan spins at the desired speed.
Enter this mode by setting bit 7 of the fan 1 or 2 config-
uration 1 register (10h and 14h) to zero and selecting
the temperature channel that controls the fan speed
using bits 2 and 3 of the configuration register.
In both RPM modes (automatic and manual), the
MAX6639 implements a low limit for the tachometer
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
Initial duty cycle
Automatic RPM Control Mode
=
Manual RPM Control Mode
255
−
t
arg
2
etTACH
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