TI中文支持网Part Number:TMS320F280049C
配置好DAC以后发现在主函数中初始化DAC后系统的采样都变的和以前不一样了，需要重新校准，但是把DAC注释掉以后系统的采样又恢复正常了，DAC会影响ADC的采样吗？
另外280049的DAC输出最大电压只能是2.5V吗？怎么设置成3.3V？
Green Deng：
你好，问题已经收到，我会跟其他同事沟通一下之后给你回复。
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Green Deng：
你好，采样值被影响具体是怎么样的趋势？
关于DAC的最大输出电压，可以参考TRM 中的下表。另外，DACVAL 应设置为最大值。
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C YG：
首先谢谢您的回复，我想问一下DAC的最大输出电压能达到3.3V吗？我下去再核实一下。
我实验中发现的现象是当DAC打开后，ADC的采样值整体偏大，就像被整体抬高了一样，重新校准后数值ADC采样仍然有小幅度差异。
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Green Deng：
你好，这个问题我咨询了一下美国工程师，对方希望能提供更详细一点的ADC采样差异情况，你方便上传一下启用DAC前后的ADC采样波形图吗？通过CCS的graph功能可以获得采样波形图
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C YG：
您好，波形没找到了，这是开启DAC以后的ADC采样数据，从原理图看到当Vbulk为400V时，分压应该是2.597V，ADC的寄存器值应该是3223，而实际实验测试到的值是4094.9几乎已经达到了最大值。
当Vbulk=300V时分压应该是1.948V，DAC值应该是2417，但是实验看到实际的ADC值是3196，几乎所有的值都被抬高了。
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Green Deng：
收到，我会尽快反馈
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Green Deng：
你好，对方工程师反馈如下，内容比较多，我就不一一翻译了，你看下：
Is HV_SENSE going directly to an ADC channel without op amp buffering? Please note that the voltage divider consisting of R46,48,49 & 51 would form a source resistance of (510K+510K+510K)||10K for an equivalent source resistance of ~9.9K. On top of this, there is a source capacitance of 1nF. External RC is too high so this will require a huge SH (not sure if ACQPS register with a max value of 511 can provide the minimum required sample and hold time), but for guidance, please refer to the the section in ADC "Choosing an Acquisition Window Duration" and try to plug in these external RC values to see the minimum SH required for such an external circuit. To increase the drive strength of the divided signal going into HV_SENSE and isolate the ADC input from the high impedance from the external RC, a strong recommendation is to use a unity gain buffer at HV_SENSE before feeding the signal to the ADC chaannel.
Now for DAC question: Once DAC output is enabled, a DAC internal load resistor in the order of a few Kohms will be connected. This would further complicate the input impedances that the ADC will see. If unbuffered, the internal DAC load would be another source of input impedance and the effect of this is that the ADC sampling capacitor will never have the chance to settle to its stable value since minimum SH time as discussed in section "Choosing an Acquisition Window Duration" would change.
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C YG：
好的，感谢您的回复
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Green Deng：
客气了
