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LMH6505: -12V into Vg pin

Jordan Lippitt
Prodigy 10 points
Part Number: LMH6505

Hi, the LMH6505 in our system runs off of +/5V and has its Vg pin driven by an op amp stage that can swing to the +/-12V rails. There is a 2.7k resistor in series between the op amp and the Vg pin. Fairly often the output of the op amp is -12V and the Vg pin is a diode drop below ground, around -0.7V. Internal protection diodes seem to be conducting and the 2.7k resistor must be limiting the current enough to survive this. My question is, do you agree that the -12V through 2.7k resistor should damage the Vg pin? 

  • +1
    TI__Expert 6050 points

    Hi Jordan,

    You are correct that the -12V through a 2.7k resistor should damage the Vg pin. As you pointed out, it is likely that the current is limited enough that the internal protection diodes are conducting and preventing damage to the chip. As specified in the datasheet, the gain control input voltage (Vg) should be in the range of 0V to 2V.

    Operating outside of this range, can cause the device to operate in adverse conditions or cause damage to the device.

    Thanks,

    Nick