LM27 datasheet(6/17 Pages) TI1

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1.8386 - VTEMP

3.552 x 10

-6

T = -1475.49 + 2.2668 x 10

6 +

LM27__L

V+

VTEMP

GND

HYST

REF

TEMP

SENSOR

V+

LM27__N

V+

VTEMP

GND

HYST

REF

TEMP

SENSOR

V+

LM27__J

V+

VTEMP

GND

HYST

REF

TEMP

SENSOR

LM27__K

V+

VTEMP

GND

HYST

REF

TEMP

SENSOR

LM27

SNIS124D – AUGUST 2002 – REVISED JULY 2013

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FUNCTIONAL DESCRIPTION

LM27 OPTIONS — Output Pin Options Block Diagrams

Figure 1. LM27-_ _J

Figure 2. LM27-_ _K

Figure 3. LM27-_ _L

Figure 4. LM27-_ _N

The LM27 can be factory programmed to have a trip point anywhere in-between 120°C to 150°C.

Applications Hints

AFTER-ASSEMBLY PCB TESTING

The LM27's VTEMP output allows after-assembly PCB testing by following a simple test procedure. Simply

measuring the VTEMP output voltage will verify that the LM27 has been assembled properly and that its

temperature sensing circuitry is functional. The VTEMP output has very weak drive capability that can be

overdriven by 1.5mA. Therefore, one can simply force the VTEMP voltage to cause the digital output to change

state, thereby verifying that the comparator and output circuitry function after assembly. Here is a sample test

procedure that can be used to test the LM27CIM5X-2HJ which has a 140°C trip point.

1. Turn on V+ and measure VTEMP. Then calculate the temperature reading of the LM27 using the equation:

VO = (−3.552×10

−6×(T−30)2) + (−10.69576×10−3×(T−30)) + 1.8386V

(2)

(3)

2. Verify that the temperature measured in step one is within (±3°C + error of reference temperature sensor) of

the ambient/board temperature. The ambient/board temperature (reference temperature) should be

measured using an extremely accurate calibrated temperature sensor, which is in close proximity to and

mounted on the same PCB as the LM27 perhaps even touching the GND lead of the LM27 if possible. The

LM27 will sence the board temperature not the ambient temperature (see MOUNTING CONSIDERATIONS)

(a) Observe that OS is high.

(b) Drive VTEMP to ground.

(d) Release the VTEMP pin.

(e) Observe that OS is now high.

(a) Observe that OS is high.

(b) Drive VTEMP voltage down gradually.

(d) VTEMPTrig = VTEMP at OS trigger (HIGH->LOW)

(e) Calculate Ttrig using Equation 3.

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