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ヒント:複数の語句はコンマで区切ってください
Date
入力例:08/09/2022
Date
入力例:08/09/2022
Global
China (简体中文)
Japan (日本語)
Korea (한국어)
Taiwan (繁體中文)
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Error sources
Power supply rejection error
Error sources
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Power supply rejection error
Hello, and welcome to the TI Precision Labs series on Current Sense amplifiers. My name is Benjamin Damkroger, and I'm a product marketing engineer in the Current position-sensing product line. In this video, we will take a closer look at power supply rejection error. In previous videos, we introduced the Root Sum of Squares, or RSS, total error equation for Current sense amplifier circuits, as shown here. Note that not all error terms may be shown. Most common error sources that are specified in typical data sheets include the following-- Input Offset Voltage, or VOS; common mode rejection ratio, or CMRR; and Power Supply Rejection Ratio, or PSRR. These errors are given in the electrical characteristics table of a device datasheet, as shown here. The rest of this video will focus on PSRR. Power supply rejection ratio is a measure of the change in devices' offset voltage-- Vos, induced by change in the amplifier supply voltage, VS. Everything else kept the same, when amplifier supply voltage changes from VSDS, the test power supply voltage given in the device electrical characteristics table, to VS-sys, the power supply voltage in an applied system, its input offset voltage changes from VOS1 to VOS2. This change is characterized by PSRR. The smaller the change in VOS, the better the PSRR spec. The equation to calculate PSRR error is shown here. It is simply the ratio of the change in VOS caused by the change of the power supply relative to the ideal shunt voltage. V Shunt_Ideal is the product of the load current and the ideal shunt resistor value, ignoring the tolerance and temperature drift of the resistor itself, which will be discussed in other videos. In device data sheets, you will find this specified either linearly, in microvolt per volt, or logarithmically, in decibels. Note that the worst case value depends on how it is specified. Let's calculate the PSRR error in an example system with a nominal load current of 20 amps and ideal shunt resistance of 1 milliohm. We'll pick the INA195 as our amplifier. The ideal shunt voltage is equal to load current times shunt resistance, which results in 20 millivolts. The supply voltage utilized in the system is 15 volts. As mentioned, if the PSRR is specified logarithmically, first it needs to be converted to a linear specification. But in this case, it is already specified linearly. Using our PSRR error equation, we calculate that the resulting error is 1.5%. The first thing most engineers will ask is, how do we make it better and minimize this error? There are two possible ways to approach this. First, you can increase the shunt voltage, which means increasing the shunt resistance. Second, you can make the PSRR spec better, which requires selecting a different device. Increasing the shunt resistance may or may not be feasible due to cost, board space, or power dissipation concerns. So let's consider option two, selecting a different device with a better PSRR spec. Let's take the same example we looked at previously, but substitute a device with improved PSRR, the INA214 at 10 microvolts per volt. As you can see, this results in an error of only 0.5%. The other factor in the numerator is the major contributor to this error. The offset is specified at a supply of 5 volts, so by using a 15-volt system supply, that delta of 10 volts is greater than in the case of the INA195, where the corresponding delta is 3 volts. Had we used the same 3-volt supply voltage delta, the PSRR error would have only been 0.15%, a 10 times improvement over INA195. Let's take a minute to summarize what we learned in this video. First, power supply rejection ratio is a measure of the change in the device's offset voltage induced by change in the amplifier's supply voltage. Secondly, power supply rejection error is calculated with respect to the ideal shunt voltage. Thirdly, power supply rejection error is proportional to the supply voltage delta. And lastly, to reduce PSRR error, you can either increase V SHUNT by increasing R SHUNT, or improve the PSRR spec by selecting a different device. That concludes this video. Thank you for watching. Please try the quiz to check your understanding of the content. For more information and videos on Current sense amplifiers, please visit ti.com/currentsense.
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説明
2019年 12月 26日
Learn more about power supply rejection error and how to minimize its effects in a current sensing application.
Download webinar slides
current-sense-amplifiers-power-supply-rejection-error-presentation-quiz.pdf
追加情報
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09:58
1
Introduction to different error sources
08:12
2
Offset error
12:21
3
Gain error
10:35
4
Common-mode rejection ratio
11:47
5
Temperature error
05:16
6
Power supply rejection error
05:39
7
Shunt resistor tolerance error
09:48
8
Output swing
17:10
9
Input filter error
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