Rainbow Electronics MAX6670 - Manual (Page 4)

MAX6668/MAX6670
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.
Remote Temperature Switches with Integrated
Fan Controller/Driver
4 _______________________________________________________________________________________
Pin Description
PIN
MAX6668 MAX6670
NAME FUNCTION
1 1 PGND Power Ground. PGND is the power ground for the FANOUT power MOSFET switch.
2 5 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
6 8 V DD Positive Power Supply
8 10 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
°C hysteresis, to V
DD for
12 °C hysteresis, or leave floating for 8°C hysteresis.