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參數(shù)資料
| 型號(hào)： | LM27A |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 【3∑C Accurate, 120∑C-150∑C Factory Preset Thermostat (LM27 in Die Form) |
| 中文描述： | 【3ΣC準(zhǔn)確，120ΣC-150ΣC工廠預(yù)設(shè)溫控器（LM27在模具中） |
| 文件頁(yè)數(shù)： | 6/10頁(yè) |
| 文件大小： | 198K |
| 代理商： | LM27A |
Applications Hints
AFTER-ASSEMBLY PCB TESTING
The LM27A's V
output allows after-assembly PCB testing
by following a simple test procedure. Simply measuring the
V
output voltage will verify that the LM27A has been as-
sembled properly and that its temperature sensing circuitry is
functional. The V
output has very weak drive capability
that can be overdriven by 1.5mA. Therefore, one can simply
force the V
voltage to cause the digital output to change
state, thereby verifying that the comparator and output cir-
cuitry function after assembly. Here is a sample test proce-
dure that can be used to test a part that would have the part
number LM27-2HJ MDA, which would have a 140°C trip point.
1.
Turn on V
+
and measure V
. Then calculate the
temperature reading of the LM27A using the equation:
V
= (3.552×10
6
×(T30)
2
) +
(10.69576×10
3
×(T30)) + 1.8386V
(1)
or
(2)
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 LM27A perhaps even
touching the GND lead of the LM27A if possible. The
LM27A will sence the board temperature not the ambient
temperature.
3.
A.
B.
C.
D.
E.
Observe that OS is high.
Drive V
TEMP
to ground.
Observe that OS is now low.
Release the V
TEMP
pin.
Observe that OS is now high.
4.
A.
B.
C.
D.
E.
Observe that OS is high.
Drive V
TEMP
voltage down gradually.
When OS goes low, note the V
TEMP
voltage.
V
TEMP
Trig = V
TEMP
at OS trigger (HIGH->LOW)
Calculate Ttrig using
Equation 2
.
5.
A.
Gradually raise V
TEMP
until OS goes HIGH. Note
V
TEMP
.
Calculate T
HYST
using
Equation 2
.
B.
V
TEMP
LOADING
The V
TEMP
output has very weak drive capability (1 μA source,
40 μA sink). So care should be taken when attaching circuitry
to this pin. Capacitive loading may cause the V
output to
oscillate. Simply adding a resistor in series as shown in
Figure
1
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 re-
sistor. If an additional capacitive load is placed directly on the
LM27A output, rather than across C
LOAD
, it should be at least
a factor of 10 smaller than C
LOAD
.
TABLE 1. Resistive compensation for capacitive loading
of V
TEMP
C
LOAD
≤
100pF
1nF
10nF
100nF
≥
1μF
R (
Ω)
0
8200
3000
1000
430
20153017
a) R in series with capacitor
20153018
b) R in series with signal path
FIGURE 1. Resistor placement for capacitive loading
compensation of V
TEMP
NOISE CONSIDERATIONS
The LM27A has excellent power supply noise rejection. Listed
below is a variety of signals used to test the LM27A power
supply rejection. False triggering of the output was not ob-
served when these signals where coupled into the V+ pin of
the LM27A.
square wave 400kHz, 1Vp-p
square wave 2kHz, 200mVp-p
sine wave 100Hz to 1MHz, 200mVp-p
Testing was done while maintaining the temperature of the
LM27A one degree centigrade way from the trip point with the
output not activated.
www.national.com
6
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| LM27CIM5-2HJ/NOPB | 功能描述:恒溫器 RoHS:否 制造商:Maxim Integrated 功能: 開(kāi)路溫度: 閉合溫度: 準(zhǔn)確性:+/- 1 C 溫度范圍:- 55 C to + 125 C 電流額定值:500 uA 電壓額定值:2.7 V to 5.5 V 產(chǎn)品:Thermostats |
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