参数资料
型号: LM27CIM5X-ZHJ
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 温度/湿度传感器
英文描述: SOT-23, 【3∑C Accurate, 120∑C-150∑C Factory Preset Thermostat
中文描述: DIGITAL TEMP SENSOR-SINGLE TRIP POINT, 3Cel, RECTANGULAR, SURFACE MOUNT
封装: PLASTIC, SOT-23, 5 PIN
文件页数: 6/10页
文件大小: 586K
代理商: LM27CIM5X-ZHJ
Functional Description
LM27 OPTIONS
The LM27 can be factory programmed to have a trip point
anywhere in-between 120C to 150C.
Applications Hints
AFTER-ASSEMBLY PCB TESTING
The LM27’s V
TEMP output allows after-assembly PCB testing
by following a simple test procedure. Simply measuring the
V
TEMP output voltage will verify that the LM27 has been
assembled properly and that its temperature sensing cir-
cuitry is functional. The V
TEMP output has very weak drive
capability that can be overdriven by 1.5mA. Therefore, one
can simply force the V
TEMP 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 140C trip point.
1.
Turn on V
+ and measure V
TEMP. Then calculate the
temperature reading of the LM27 using the equation:
V
O = (3.552x10
6x(T30)2)+
(10.69576x10
3x(T30)) + 1.8386V
(1)
or
(2)
2.
Verify that the temperature measured in step one is
within (±3C + error of reference temperature sensor) of
the ambient/board temperature. The ambient/board tem-
perature (reference temperature) should be measured
using an extremely accurate calibrated temperature sen-
sor, 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
Section Titled Mounting Considerations)
3.
A. Observe that OS is high.
B. Drive V
TEMP to ground.
C. Observe that OS is now low.
D. Release the V
TEMP pin.
E. Observe that OS is now high.
4.
A. Observe that OS is high.
B. Drive V
TEMP voltage down gradually.
C. When OS goes low, note the V
TEMP voltage.
D. V
TEMPTrig=VTEMP at OS trigger (HIGH->LOW)
E. Calculate Ttrig using Equation (2).
5.
A. Gradually raise V
TEMP until OS goes HIGH. Note
V
TEMP.
B. Calculate T
HYST using Equation (2).
V
TEMP LOADING
The V
TEMP output has very weak drive capability (1 A
source, 40 A sink). So care should be taken when attaching
circuitry to this pin. Capacitive loading may cause the V
TEMP
output to oscillate. Simply adding a resistor in series as
shown in Figure 2 will prevent oscillations from occurring. To
determine the value of the resistor follow the guidelines
given in Table 1. The same value resistor will work for either
placement of the resistor. If an additional capacitive load is
placed directly on the LM27 output, rather than across
C
LOAD, it should be at least a factor of 10 smaller than
C
LOAD.
20030712
LM27-_ _J
20030713
LM27-_ _K
20030714
LM27-_ _L
20030715
LM27-_ _N
FIGURE 1. Output Pin Options Block Diagrams
LM27
www.national.com
5
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