LM56
Functional Description
DS012893-15
1.0 PIN DESCRIPTION
V
+
This is the positive supply voltage pin. This pin
should be bypassed with 0.1 µF capacitor to
ground.
GND
V
REF
This is the ground pin.
This is the 1.250V bandgap voltage reference out-
put pin. In order to maintain trip point accuracy this
pin should source a 50 µA load.
This is the temperature sensor output pin.
This is an open collector digital output. OUT1 is ac-
tive 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 in-
tended to directly drive a fan motor.
This is an open collector digital output. OUT2 is ac-
tive 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
voltage for OUT1.
This is the input pin for the low temperature trip
point voltage for OUT2.
V
TEMP
OUT1
OUT2
DS012893-16
V
T1
V
T2
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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