zero, the duty cycle is zero below the fan-start tempera-
ture and has this value when the fan-start temperature
is reached. A value of 240 represents 100% duty cycle.
Writing any value greater than 240 causes the fan
speed to be set to 100%. The POR state of the fan-start
duty-cycle register is 60h, 40%.
PWMOUT Max Duty Cycle (09h and 0Ah)
The PWM maximum duty-cycle register sets the maxi-
mum allowable PWM duty cycle between 2/240 (0.83%
duty cycle) and 240/240 (100% duty cycle). Any values
greater than 240 are recognized as 100% maximum
duty cycle. The POR state of the PWM maximum duty-
cycle register is F0h, 100%. In manual-control mode,
this register is ignored.
PWM Target Duty Cycle (0Bh and 0Ch)
In automatic fan-control mode, this register contains the
present value of the target PWM duty cycle, as deter-
mined by the measured temperature and the duty-
cycle step size. The actual duty cycle requires time
before it equals the target duty cycle if the duty-cycle
rate-of-change register is set to a value other than zero.
In manual fan-control mode, write the desired value of
the PWM duty cycle directly into this register. The POR
state of the fan-target duty-cycle register is 00h.
PWM1 Instantaneous Duty Cycle,
PWM2 Instantaneous Duty Cycle (0Dh, 0Eh)
These registers always contain the duty cycle of the
PWM signals presented at the PWM output.
The POR state of the PWM instantaneous duty-cycle
register is 00h.
Channel 1 and Channel 2 Fan-Start Temperature
(0Fh and 10h)
These registers contain the temperatures at which fan
control begins (in automatic mode). See the
Automatic
PWM Duty-Cycle Control
section for details on setting
the fan-start thresholds. The POR state of the channel 1
and channel 2 fan-start temperature registers is 00h.
Fan Configuration (11h)
The fan-configuration register controls the hysteresis
level, temperature step size, and whether the remote or
local diode controls the PWM2 signal (see Table 3). Set
bit D7 of the fan-configuration register to zero to set the
hysteresis value to 5°C. Set bit D7 to 1 to set the hys-
teresis value to 10°C. Set bit D6 to zero to set the fan-
control temperature step size to 1°C. Set bit D6 to 1 to
set the fan-control temperature step size to +2°C. Bits
D5 to D2 select which PWM_ channel 1 or channel 2
controls (see Table 3). If both are selected for a given
PWM_, the highest PWM value is used. If neither is
selected, the fan is controlled by the value written to the
fan-target duty-cycle register. Also in this mode, the value
written to the target duty-cycle register is not limited by
the value in the maximum duty-cycle register. It is, howev-
er, clipped to 240 if a value above 240 is written. The
POR state of the fan-configuration register is 00h.
Duty-Cycle Rate of Change (12h)
Bits D7, D6, and D5 (channel 1) and D4, D3, and D2
(channel 2) of the duty-cycle rate-of-change register set
the time between increments of the duty cycle. Each
increment is 2/240 of the duty cycle (see Table 5). This
allows the time from 33% to 100% duty cycle to be
adjusted from 5s to 320s. The rate-of-change control is
always active in manual mode. To make instant changes,
set bits D7, D6, and D5 (channel 1) or D4, D3, and D2
(channel 2) = 000. The POR state of the duty-cycle rate-
of-change register is B4h (1s between increments).
MAX6615/MAX6616
Dual-Channel Temperature Monitors and
Fan-Speed Controllers with Thermistor Inputs
______________________________________________________________________________________ 15
Table 5. Setting the Time Between Duty-
Cycle Increments
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