MAX6653/MAX6663/MAX6664
Temperature Monitors and
PWM Fan Controllers
10 ______________________________________________________________________________________
INT is an open-drain digital output that reports the sta-
tus of temperature interrupt limits and fan out-of-limit
conditions. Set bit 1 of configuration register 1 (00h) to
1 to enable INT output or reset this bit to zero to disable
the INT output function. Status register 1 contains sta-
tus information for the conditions that cause INT to
assert. Reading status register 1 resets INT, but INT is
reasserted if the fault condition still exists. Connect a
10kΩ pullup resistor between INT and V
CC
.
SDL and SDR are open-drain digital outputs on the
MAX6653 that can be used to shut the system down
based on the local (die) temperature of the MAX6653 or
the temperature of the remote sensor, respectively. The
trip thresholds for SDL and SDR are normally set above
the THERM and INT limits. Their power-up values are
set by the CRIT1 and CRIT0 pins, as shown in Table 1.
Fan-Speed Control
The MAX6653/MAX6663/MAX6664 fan-control section
can operate in one of three modes depending on the set-
ting of bit 7 to bit 5 of configuration register 1 (00h).
Regardless of the mode of operation, the PWM output fre-
quency is programmable, and the fan speed is measured
with the result stored in the fan-speed register (08h).
PWM Output Frequency
The PWM output frequency is programmed by bit 5, bit
4, and bit 3 of the fan characteristics register (20h),
regardless of the mode of operation. See Table 7.
Fan-Control Mode
The mode of fan-speed control operation is set by bit 7,
bit 6, and bit 5 in configuration register 1 (00h), as
shown in Table 8.
PWM Duty-Cycle Fan-Control Mode
Bits [3:0] of the fan-speed configuration register set the
PWM duty cycle. See Table 9 for more details.
RPM Select Fan-Control Mode
In RPM select mode, the MAX6653/MAX6663/MAX6664
adjust their PWM output duty cycle to match a selected
fan speed measured by a tachometer count value. Before
selecting this mode by setting bits [7:5] of configuration
register 1 (00h) to 0x1, the desired tachometer count
value should be written to the fan tachometer high-limit
register (10h). In this mode, the MAX6653/MAX6663/
MAX6664 are not able to detect underspeed fan faults
because the fan tachometer high-limit register (10h) func-
tions as the target tachometer count.
The MAX6653/MAX6663/MAX6664 detect fan stall
faults by comparing the fan-speed reading to the full-
scale constant of 254 (FEh). Therefore, the
MAX6653/MAX6663/MAX6664 signal a fan fault when
the fan-speed reading is 255 (FFh). Note that the RPM
mode cannot be used for speeds below 10% of the
fan’s maximum speed. It is important to verify that a fan
works properly at lower RPM values if a low-RPM oper-
ation in this mode is desired.
configuration register (22h).
Program the desired fan speed by writing to the fan tachometer high-limit register
(10h). This value should be written after selecting the RPM mode. The
spin at the programmed speed.
temperatures. See the Automatic Fan-Control Mode section.
