参数资料
| 型号： | AS8501-ASOT |
| 厂商： | ams |
| 文件页数： | 29/41页 |
| 文件大小： | 0K |
| 描述： | IC CURRENT MEASURE SOLAR 16-SOIC |
| 标准包装： | 1,500 |
| 类型： | 数据采集系统（DAS） |
| 输入类型： | 模拟，数字 |
| 输出类型： | 模拟，数字 |
| 接口： | 串行 |
| 电流 - 电源： | 5mA |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 16-SOIC |
| 包装： | 带卷 (TR) |
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AS8501 - Data Sheet
austriamicrosystems
Revision 1.1, 04-April-06
www.austriamicrosystems.com
Page 34 of 40
9
General application hints
Since the AS8501 is optimised for low voltage applications extreme care should be taken that the signal is not disturbed by influences like bad ground
reference, external noise pick-up, thermal EMFs generated at the transition of different materials or ground loops. The influence of these error sources
can be quite high and they may completely shadow the excellent properties of the device if not handled properly. The following sections are supposed
to supply additional informations to the design engineer how to get around some of these problems.
9.1
Ground connection, analog common
The analog common terminal where all voltages are referring to is RSHL. All ground lines of the external circuitry of VBAT, ETS and ETR as well as the
voltage sense line of the low ohmic current sensing resistor should be connected to each other in a star like ground point. It is recommended that this
point is as close as possible situated to the low side sense terminal of the current sensing resistor. It should also be connected to the VSS and VSSD
terminal, but the return line of both must leave this point separately. Also the power decoupling capacitors should be connected to the analog common.
To give an example of the magnitude of possible errors consider that the ground return of the power supply is not connected properly and 5 mm of a
copper track 35m thick and 0.1 mm wide are within the measuring circuit with a current flow of 5 mA. This will result in an offset of 120 V which is
more than 500 times higher than the typical offset of the ASSP. In addition the current fluctuations will act as an extra noise voltage which is also way
above that of the device itself.
9.2
Thermal EMF
another major source of error for low level measurements are thermal voltages (electromotive force, thermal EMF) or Seebeck voltages which are
principally produced by any junction of two dissimilar materials. On PC-boards pairs of dissimilar materials may consist of the copper tracks and the
solder, the leads of different components or different materials used in the construction within the components. Any temperature difference between
two connection produces a voltage which is superimposed to the measuring voltage.
A number of strategies are known to detect or minimise their influence on the measuring result:
-
in cases were a current has to be measured directly or a current is to be used to activate a resistive sensor (like
Ohm-meter or temperature measurement with RTDs, NTC or PTC) a switch in the circuit could be used to interrupt or invert the current thus
producing a current change dI. In the difference of the two voltage states dU the EMFs as well as the Offset voltages of the amplifier are fully
eliminated. For resistance measurements this method is known as ‘true Ohm’ measurement.
-
in applications were this is not possible and the problematic device (i.e. the input resistor of an amplifier) can be located it may help to place a
dummy device of the same type in the circuit as close and thermally connected as good as possible to compensate the influence of the first one.
-
Since the thermal EMFs are proportional to the temperature difference it is important to maintain a homogeneous temperature distribution in the
vicinity of the sensitive area. This is possible by keeping this area as small as possible, by avoiding any heat sources nearby or by increasing the
heat conductivity of the substrate, i.e. wide and thick copper tracks, multilayer board or even metal substrate.
-
The best solution of all however is to avoid the thermal EMFs by using only components which are matched to the copper world which means
that their thermo-electrical power against copper is zero. This is specially important for current measurements in the range of 10- 1000A. In this
case the resistance value has to be very low (down to 100Ohms) to limit the measuring power and avoid an overheating of the sensing resistor.
On the other hand the voltages to be detected are extremely low if a high resolution is required. If for instance a current of 10 mA has to be
measured with a 100Ohm resistor, the resolution of the measuring system must be better than 1V and the error voltages due to thermal EMFs
must be below this limit. Quite often people are trying to use the well known Konstantan (CuNi44) for current sensing resistors. This is a bad
choice since the thermal EMF versus copper is very high.
With –40V/deg already a temperature difference of
2.5 K is enough to produce an error which is 100 times lager than the required resolution. Or vice versa a temperature fluctuation of only 1/100 K
produces a ‘thermal noise’ which is equivalent to the required resolution.
With such materials and high currents of 10A and above the other thermoelectric effect, the so called Peltier-effect, can also play an important
role. Under current flow this effect generates heat in one junction and destroys the same amount of heat in the other junction. The amount of
heat is proportional to the current and its direction. The result is a temperature difference which in turn generates a thermal EMF proportional to it.
Finally this means that such a resistor produces its own error voltage and it is never possible to measure better than 1-2% with such badly
matched materials. The precision resistance materials Manganin, Zeranin and Isaohm are perfectly matched to the copper world and resistors
made from these materials can achieve the high quality that is necessary for low
ams
AG
Technical
content
still
valid
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相关代理商/技术参数 |
参数描述 |
|---|---|
| AS8501-ASOU | 功能描述:IC DATA ACQ 16-SOIC RoHS:是 类别:集成电路 (IC) >> 接口 - 传感器和探测器接口 系列:- 其它有关文件:Automotive Product Guide 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:74 系列:- 类型:触控式传感器 输入类型:数字 输出类型:数字 接口:JTAG，串行 电流 - 电源:100µA 安装类型:表面贴装 封装/外壳:20-TSSOP（0.173"，4.40mm 宽） 供应商设备封装:20-TSSOP 包装:管件 |
| AS8501T&R | 制造商:AMSCO 制造商全称:austriamicrosystems AG 功能描述:High precision voltage and current measurement sensor interface |
| AS8501TR | 制造商:AMSCO 制造商全称:austriamicrosystems AG 功能描述:High precision voltage and current measurement sensor interface |
| AS8501TUB | 制造商:AMSCO 制造商全称:austriamicrosystems AG 功能描述:High precision voltage and current measurement sensor interface |
| AS85049-32-1 | 制造商:GLENAIR 制造商全称:Glenair, Inc. 功能描述:90° Adapter, Non-Environmental, RFI |
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