LM56
Functional Description
01289315
Pin Descriptions
This is the positive supply voltage pin. This pin
should be bypassed with a 0.1 µF capacitor to
ground.
GND This is the ground pin.
V
REF
This is the 1.250V bandgap voltage reference output
pin. In order to maintain trip point accuracy this pin
should source a 50 µA load.
V
TEMP
This is the temperature sensor output pin.
OUT1 This is an open collector digital output. OUT1 is
active LOW. It goes LOW when the temperature is
greater than T
1
and goes HIGH when the tempera-
ture drops below T
1
– 5˚C. This output is not intended
to directly drive a fan motor.
OUT2 This is an open collector digital output. OUT2 is
active LOW. It goes LOW when the temperature is
greater than the T
2
set point and goes HIGH when
the temperature is less than T
2
– 5˚C. This output is
not intended to directly drive a fan motor.
This is the input pin for the temperature trip point
V
T1
voltage for OUT1.
This is the input pin for the low temperature trip point
V
T2
voltage for OUT2.
V
+
01289316
V
T1
= 1.250V x (R1)/(R1 + R2 + R3)
V
T2
= 1.250V x (R1 + R2)/(R1 + R2 + R3)
where:
(R1 + R2 + R3) = 27 kΩ and
V
T1 or T2
= [6.20 mV/˚C x T] + 395 mV therefore:
R1 = V
T1
/(1.25V) x 27 kΩ
R2 = (V
T2
/(1.25V) x 27 k)Ω–R1
R3 = 27 kΩ − R1 − R2
7
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