MPC5744 ADC 采样通道第一次切换时结果偏小

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MPC5744 ADC 采样通道第一次切换时结果偏小

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xaing_wang
Contributor I

大家好,

   我们电机控制系统是低端3电阻采样,使用MPC5744,CTU控制一个控制周期采样其中两相电流,在扇区切换,需要切换ADC通道的时候,出现了一个问题,切换的这个通道采样值偏低,导致q轴电流出现凸起波动,第二个控制周期采样的相电流和后面采样的相电流差值就比较均匀。如下图所示第一行曲线是实际q轴电流,第二行曲线是采样的两个电流AD值,第三个是扇区,q轴电流每一个凸起地方都是ADC通道切换地方,最后一个凸起地方对应的AD采样通道切换的AD结果明显出现偏低,图形放大后可以看到,与后一个控制周期电流AD相差大约60个AD值,正常大约20个AD,如图二所示。

请问各位NXP专家,CTU 的CMD list ADC通道在从采样ADC0 通道0+和ADC1通道2同步采样  切换为  ADC0通道0+ADC1通道3同步采样,切换之后ADC1 通道3的采样结果是否会偏小呢?怎么避免偏小,保证采样准确呢?已经确认了切换成功了,通过下图电流波形也可与看出来。以上通道是只是举例子。

q轴电流凸起.jpg实际采样结果偏差.jpg

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PetrS
NXP TechSupport
NXP TechSupport

Hi,

please try to use English to describe the issue. From the translator I understand the measurement of one phase on ADC1 looks little bit low. It could be fine if you can share the ADC circuitry you have. Also compare ADC measurement with real phase measurement taken with scope, which I think is not shown on the pictures. If you have a possibilities try to use different ADC channels on MCU. Does anything change if the ADC channel presampling is enabled?

BR, Petr

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xaing_wang
Contributor I

Hi,Petr,thank you for your response!

The picture below is ADC circuitry,TP548、TP551、TP553 is op amp output,R529/R530/R531 is 100Ω,C524/C526/C527 is 6.8nF。And the real phase measurement signal is current,it is very low voltage,Let me try。 

微信截图_20200113131248.png

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2548903578
Contributor III

你好!

我想请问你一下 你有在ADC的代码中加入操作系统吗?

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xaing_wang
Contributor I

没有

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