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LM358 / about negative input voltage

Sho Ogane
Genius 5575 points

Other Parts Discussed in Thread: LM358

Hi all.

My customer use the LM358 with voltage follower.
They input negative voltage to IN+.
Using condition is the following
・Vcc+=15V,Vcc-=-15V
Please tell me the lower limit of the negatve voltage.
And is the IC broken?

Best Regards,
Sho
0743.LM358.pdf

  • 0
    TI__Guru 64896 points
    Hello Sho,

    The lower input voltage would be -15.3V, or 300mV below V- ('GND' pin). Going further can cause a malfunction or cause latching or damage to the substrate of the device if the current is not limited.

    However, in your schematic, there should be a current limiting resistor (1k min) between the output and the clamping diodes. If the input is outside the 0 to 3.3V window, the output will be dumping current into ground or the 3.3V supply.

    Also, the amplifier is capable of lifting the 3.3V supply above 3.3V. Most regulators are source-only, and cannot sink current, so it is possible to "pull" the 3.3V supply line higher than the regulator output. There should be a 3.6V Zener diode on the 3.3V supply to prevent the 3.3V supply from being lifted above 3.6V.

    Regards,