LM56
Functional Description
1289315
Pin Descriptions
V
+
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 temperature 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 tem-
perature is less than T
2
– 5°C. This output is not in-
tended to directly drive a fan motor.
V
T1
This is the input pin for the temperature trip point volt-
age for OUT1.
V
T2
This is the input pin for the low temperature trip point
voltage for OUT2.
1289316
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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