Detailed Description

The MAX6668/MAX6670 are simple fan controllers/dri-

vers that turn on an internal power transistor when the

sensed temperature of an external P-N junction

exceeds a factory-set threshold. By connecting a small

(up to +12V/250mA nominal) cooling fan to FANOUT, a

simple on/off fan-control system is created. Do not con-

nect the fan to a power supply of higher than 12V nomi-

nal, 15V maximum.

FANOUT Driver and FORCEON Controller

FANOUT Fan-Driver Output

FANOUT is an open-drain output that sinks greater than

250mA of current to turn on the fan, either when the fan

trip threshold is exceeded or the fan is forced on by dri-

ving FORCEON low.

FORCEON Fan-Control Input

Drive FORCEON low to turn on the fan when the

MAX6670’s remote-sensing junction temperature is less

than the fan trip threshold temperature. This overrides

the internal control circuitry and allows for an external

device to activate the fan.

Overtemperature Alarm Outputs

WARN Output (MAX6670 Only)

WARN is an active-low, open-drain digital output that

indicates when the external P-N junction’s temperature

exceeds 15°C above the fan trip threshold. The WARN

output serves as a warning that the system temperature

has continued to rise well above the fan activation tem-

perature.

OT Output (MAX6670 Only)

OT is an active-low, open-drain digital output that indi-

cates when the external P-N junction’s temperature

exceeds 30°C above the fan trip threshold. OT serves

as a thermal shutdown output to the system in case of

excessive temperature rise.

Hysteresis Input

The temperature comparator has hysteresis to prevent

small temperature changes near the threshold temper-

ature from causing the fan to turn on and off repeatedly

over short periods of time. The FANOUT pin goes

active and powers the fan when the external P-N junc-

tion’s temperature exceeds the factory-programmed

Remote Temperature Switches with Integrated

Fan Controller/Driver

4

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Pin Description

PIN

MAX6668

MAX6670

NAME

FUNCTION

1

1

PGND

Power Ground. PGND is the power ground for the FANOUT power MOSFET switch.

25

FORCEON

Fan-Control Input. Drive FORCEON high for normal operation. Drive FORCEON low

to force fan on.

3

3

DXP

Current Source Positive Input. Connect to the anode of the external diode-

connected transistor. Do not leave DXP floating. Connect a 2200pF capacitor

between DXP and DXN for noise filtering.

4

4

DXN

Current Sink Negative Input. Connect to the cathode of the external diode-

connected transistor. DXN is internally biased to a diode voltage drop.

5, 7

7

GND

Ground

68

Positive Power Supply

810

FANOUT

Fan-Drive Output. FANOUT is an open-drain power MOSFET that sinks up to 250mA

current to turn on the fan when the sensed temperature exceeds the fan trip

threshold or the fan is forced on by driving FORCEON low.

—

2

WARN

Temperature Warning Output. WARN is an open-drain output that goes low when

the sensed junction temperature is 15

°C higher than the fan trip threshold.

—

6

OT

Overtemperature Output. OT is an open-drain output that goes low when the sensed

junction temperature is 30

°C higher than the fan trip threshold.

—

9

HYST

Hysteresis Control Input. HYST is a three-level logic input for controlling the fan-

drive comparator’s hysteresis. Connect HYST to GND for 4

12

°C hysteresis, or leave floating for 8°C hysteresis.