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LM358: hardware issue

Part Number: LM358

 您好,有个问题请教下,

1KVIN+和1KVIN-是加了600V电压


5V2和5V2GND是金升阳的电源模块隔离出来的


我把R236去掉了,跟后级断开了


老批次的358,输出1.2V(1脚和4脚)。新批次的358,输出0.5V左右

  • What are the voltages at pins 2,3,5,6,7?

  • 1脚对4脚,2脚对4脚,3脚对4脚,5脚对4脚,6脚对4脚,7脚对4脚的电压分别为-4.6mV,-6.4mV,-0.536V,0.59V,-0.666V,-0.568V,thanks

  • Negative voltages at the inputs are outside the valid common-mode range (see section 6.3 of the datasheet), so correct operation cannot be guaranteed.

    Furthermore, voltages below −0.3 V are outside the absolute maximum ratings (section 6.1), so the device can be damaged.

    You need a different circuit that scales down both inputs voltage into the valid range before the arrive at the opamp inputs. At a minimum, the reference voltage (the lower end of R232) should not be GND but be high enough to avoid negative voltages.

  • LM358硬件问题

    一、问题说明

        在使用LM358时发现,同一型号不同批次的器件焊接至PCB,功能出现异常。原理示意图如下,特别说明,电池与运放不共地。

    使用墨西哥批次358,各节点电压

    图1.墨西哥批次358

    使用马来西亚批次358,各节点电压

    图2. 马来西亚批次358

     

    二、TI答复

    TI技术人员针对图2进行答复,如下:

    1.输入端的负电压在有效的共模范围之外(见数据表第6.3),因此不能保证正确的操作。

    2.此外,低于- 0.3 V的电压超出绝对最大额定值(6.1),因此设备可能会损坏。

    3.您需要一个不同的电路,在到达运放输入之前将两个输入电压降至有效范围。至少,参考电压(R232的下端)不应该是GND,但应该足够高以避免负电压

    三、疑问

       针对答复,有几处不明确的地方,还请指教

    1. 答复1中的输入端共模电压是否指的是 (-0.673+0.615/2=-0.029<0,因此不能保证芯片正常工作
    2. 答复2中的低于-0.3V的电压是否指的是6脚的-0.673V
    3. 针对图1中的墨西哥批次358,输入端共模电压是否是 (628+0.629/2=0.6285,是否可以理解处在共模范围之内。若在范围之内,图1中的电路是否还存在不合理之处。

     

  • (I am not a TI employee.)

    1. The datasheet specifies common-mode voltage limits because it assumes that the circuit has proper negative feedback that results in both inputs having the same voltage. But these limits apply to both input pins, individually.

    2. The voltage at pin 6 indeed exceeds the limits.

    3. The voltages in the first image are correct.