Automatic PWM Fan-Speed Controllers with
Overtemperature Output
MAX6643
1, 15
2, 3
4
5
6
—
7
8
—
9
10, 11
PIN
MAX6644
1, 15
2, 3
4
5
—
—
7
—
6, 8
9
10, 11
Pin Description
MAX6645
—
—
1
2
—
—
4
—
3, 5
6
7, 8
NAME
FUNCTION
TH1, TH2
TL2, TL1
FANFAIL
High-Temperature Threshold Inputs. Connect to VDD, GND, or
leave unconnected to select the upper fan-control trip
temperature (THIGH), in 5°C increments. See Table 1.
Low-Temperature Threshold Inputs. Connect to VDD, GND, or
leave unconnected to select the lower fan-control trip
temperature (TLOW), in 5°C increments. See Table 2.
Fan-Fail Alarm Output. FANFAIL is an active-low, open-drain
output. If the FAN_IN_ detects a fan failure, the FANFAIL output
asserts low.
TACHSET
FAN_IN_ Control Input. TACHSET controls what type of fan-fail
condition is being detected. Connect TACHSET to VDD, GND,
or leave floating to set locked rotor, current sense, or
tachometer configurations (see Table 3).
FULLSPD
Active-High Logic Input. When pulled high, the fan runs at
100% duty cycle.
FULLSPD Active-Low Logic Input. When pulled low, the fan runs at 100%
duty cycle.
GND
Ground
DXP
DXP2, DXP1
Combined Current Source and A/D Positive Input for Remote
Diode. Connect to anode of remote diode-connected
temperature-sensing transistor. Connect to GND if no remote
diode is used. Place a 2200pF capacitor between DXP_ and
GND for noise filtering.
OT
Active-Low, Open-Drain Overtemperature Output. When OT
threshold is exceeded, OT pulls low.
FAN_IN2,
FAN_IN1
Fan-Sense Input. FAN_IN_ can be configured to monitor either a
fan’s logic-level locked-rotor output, tachometer output, or sense-
resistor waveform to detect fan failure. The MAX6643’s FAN_IN_
input can monitor only tachometer signals. The MAX6644 and the
MAX6645 can monitor any one of the three signal types as
configured using the TACHSET input.
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