- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385936 > TMP12FS (Analog Devices, Inc.) Airflow and Temperature Sensor PDF資料下載
參數(shù)資料
| 型號： | TMP12FS |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Airflow and Temperature Sensor |
| 中文描述： | 氣流和溫度傳感器 |
| 文件頁數(shù)： | 10/14頁 |
| 文件大?。?/td> | 446K |
| 代理商： | TMP12FS |
TMP12
REV. 0
–10–
Understanding Error Sources
The accuracy of the VPTAT sensor output is well characterized
and specified, however preserving this accuracy in a thermal
monitoring control system requires some attention to minimiz-
ing the various potential error sources. The internal sources of
setpoint programming error include the initial tolerances and
temperature drifts of the reference voltage VREF, the setpoint
comparator input offset voltage and bias current, and the hyster-
esis current scale factor. When evaluating setpoint programming
errors, remember that any VREF error contribution at the com-
parator inputs is reduced by the resistor divider ratios. Each
comparator’s input bias current drops to less than 1 nA (typ)
when the comparator is tripped. This change accounts for some
setpoint voltage error, equal to the change in bias current multi-
plied by the effective setpoint divider ladder resistance to ground.
The thermal mass of the TMP12 package and the degree of
thermal coupling to the surrounding circuitry are the largest fac-
tors in determining the rate of thermal settling, which ultimately
determines the rate at which the desired temperature measure-
ment accuracy may be reached (see graph in Figure 3). Thus,
one must allow sufficient time for the device to reach the final
temperature. The typical thermal time constant for the SOIC
plastic package is approximately 70 seconds in still air. There-
fore, to reach the final temperature accuracy within 1%, for a
temperature change of 60 degrees, a settling time of 5 time con-
stants, or 6 minutes, is necessary. Refer to Figure 4.
External error sources to consider are the accuracy of the external
programming resistors, grounding error voltages, and thermal gra-
dients. The accuracy of the external programming resistors directly
impacts the resulting setpoint accuracy. Thus, in fixed-temperature
applications the user should select resistor tolerances appropriate
to the desired programming accuracy. Since setpoint resistors are
typically located in the same air flow as the TMP12, resistor tem-
perature drift must be taken into account also.
This effect can be
minimized by selecting good quality components, and by keep-
ing all components in close thermal proximity. Careful circuit
board layout and component placement are necessary to mini-
mize common thermal error sources. Also, the user should take
care to keep the bottom of the setpoint programming divider
ladder as close to GND (Pin 4) as possible to minimize errors
due to IR voltage drops and coupling of external noise sources.
In any case, a 0.1
μ
F capacitor for power supply bypassing is
always recommended at the chip
.
Safety Considerations in Heating and Cooling System Design
Designers should anticipate potential system fault conditions
that may result in significant safety hazards which are outside
the control of and cannot be corrected by the TMP12-based cir-
cuit. Governmental and Industrial regulations regarding safety
requirements and standards for such designs should be observed
where applicable.
Self-Heating Effects
In some applications the user should consider the effects of self-
heating due to the power dissipated by the open-collector outputs,
which are capable of sinking 20 mA continuously. Under full load,
the TMP12 open-collector output device is dissipating:
P
DISS
= 0.6
V
0.020
A
= 12
mW
which in a surface-mount SO package accounts for a tempera-
ture increase due to self-heating of:
T
=
P
DISS
JA
=
0.012
W
158
°
C/W
= 1.9
°
C
This increase is for still air, of course, and will be reduced at
high airflow levels. However, the user should still be aware that
self-heating effects can directly affect the accuracy of the
TMP12. For setpoint 2, self-heating will add to the setpoint
temperature (that is, in the above example the TMP12 will
switch the setpoint 2 output off 1.9 degrees early). Self-heating
will not affect the temperature at which setpoint 1 turns on, but
will add to the hysteresis. Several circuits for adding external
driver transistors and other buffers are presented in following
sections of this data sheet. These buffers will reduce self-heating
and improve accuracy.
Buffering the Voltage Reference
The reference output VREF is used to generate the temperature
setpoint programming voltages for the TMP12. Since the hyster-
esis is set by the reference current, external circuits which draw
current from the reference will increase the hysteresis value.
5
6
7
8
OP193
VREF
SET
HIGH
SET
LOW
GND
V+
HEATER
1
2
3
4
TMP12
130k
+5V
~1.5V
200k
5k
NC
NC
+5V
+5V
1uF
300k
10k
0.1UF
VPTAT
OVER
UNDER
Figure 22. An Analog Measurement Circuit for VPTAT
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| TMP12GBC | Airflow and Temperature Sensor |
| TMP17 | Low Cost, Current Output Temperature Transducer |
| TMP17FS | Low Cost, Current Output Temperature Transducer |
| TMP17GS | Low Cost, Current Output Temperature Transducer |
| TMP320C40KGDC | Floating-Point Digital Signal Processor Known Good Die(6個通訊口，獨立的智能DMA協(xié)處理器) |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| TMP12FS-REEL | 制造商:Analog Devices 功能描述:Temp Sensor Digital Serial (3-Wire) 8-Pin SOIC T/R |
| TMP12FSZ | 制造商:Analog Devices 功能描述:Temp Sensor Digital Serial (3-Wire) 8-Pin SOIC |
| TMP12GBC | 制造商:AD 制造商全稱:Analog Devices 功能描述:Airflow and Temperature Sensor |
| TMP130 | 制造商:TRUMPOWER 制造商全稱:Tumbler Technologies + TRUMPower 功能描述:130 WATT MEDICAL POWER ADAPTERS |
| TMP130-05 | 制造商:TRUMPOWER 制造商全稱:Tumbler Technologies + TRUMPower 功能描述:130 WATT MEDICAL POWER ADAPTERS |
發(fā)布緊急采購，3分鐘左右您將得到回復。