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PGA281使用中遇到的问题

Other Parts Discussed in Thread: PGA281

     各位工程师,你们好!我把PGA281设置为单端输入和单端输出,供电为正负5V,原理图如下所示:

在实际电路板中,芯片为申请的样品,出现了以下问题:

测试条件:供电正常,将G4~G0全部接地,没有信号输入,其它引脚供电电压正常。

1:在焊接分压电阻之后,VOCM=2.5V,在焊接芯片之后,VOCM=1.75V,电路输出VOP=1.79V,这有可能因为什么原因导致的呢?

2:EF端一直输出3.3V,表明电路出现了问题,不知道哪里出现了问题?

麻烦各位工程师解答了!!!

  • 不知道你怎么焊接的, 难道是电烙铁的静电打坏了芯片了
    不过, 你还是先检查一下
    电路图和 PCB 板的走线是否一致,
    以及焊接质量, 有没有虚焊情况.
  • 这个是EF引脚输出为高的几种情况,通过您的描述,输入信号悬空,会导致内部运放A1,A2输出饱和。

    所以我的建议是,先检查下焊接情况,在焊接无误的前提下,正确给输入信号,看PGA281 功能是否正常。

  • 您好!在仔细检查电路之后,焊接没有问题,由于2.5V参考电压不对,我断开VOCM,将下面电路接入,作为PGA281参考电压:

    在将增益设置为1,PGA281能正常输出正弦波信号,但是信号输出的参考电压是2.2V,正弦波围绕2,2V输出,增益倍数与设定整体符合,但是误差很大,但此时给定VOCM=2.5V。有几个问题想要请教一下:

    1:我的最原始电路是不是有问题,有哪里可以修改一下?

    2;PGA281是不是不适合作为单端使用?如果不适合,我后续可能改为单端输入,差分输出。

  • 原始电路没没看出什么问题,单端输出不是不可以,单端输出的话,那么理论上幅值变为一半,或者说增益相当于配置的一半。 单端输出的还一个缺点就是不能抑制共模电压(差分输出的话共模为0),以及各种噪声,GND error带来的误差。 您参考下PGA281 关于单端输出的这部分介绍:

    Single-Ended Output
    The output stage of the PGA281 is designed for highest precision. The fully-differential output avoids grounding
    errors and noise, and delivers twice the signal amplitude compared to single-ended signals. However, if desired,
    a single-ended output (VOP or VON) can be measured, referred to the voltage at the VOCM pin. The output
    stage errors now relate to half the signal amplitude and half the signal gain. Figure 43 shows how the unused
    output is unconnected, but not disconnected from error detection. The usable voltage range for the VOCM input
    is specified in the Electrical Characteristics and must be observed; that is, the output swing (of both outputs)
    should not saturate to the supply. Separate specifications for offset voltage and drift indicate higher offset voltage
    at lower gains because some error sources are not cancelled in the output stage connected in single-ended
    mode. Note that the gain is one-half of the gain set in reference to the gain table (see Table 1).