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LMV641: LMV641 Damage.

Ian Wang
Mastermind 28065 points
Part Number: LMV641
Other Parts Discussed in Thread: LM324A

Hi Sir,

My customer using op amp as integrator for gain & adding bias to analog signal (please see the illustration below), Op Amp V+ = 3.3V, V- = 0V

The usage is that want to shift audio analog signal up 1.65V to get it into MCU ADC to process (MCU ADC input range 0~3.3V)

For both LMV641 & LM324A, the spec for abs. min input pin voltage should no lower than -0.3V:

LMV641,

Is this due to protection diode on the input pin?

LMV641’s spec has no internal block diagram so not sure. 

LMV641 was permanently damaged after gave vin- analog sine tone signals over 500mVrms (over 700mV ~ -700mV), though LM324A had no issue with 2Vrms input

Questions:

  1. Is the absolute min & max voltage add/minus 0.3V from the supply voltage due to protection diode? Or is there other concerns?
  2. If using LM324A for this application (Vin- can range from 2.8V ~ -2.8V) seems no problem so far, though is there any long term concern? Or we really need op amp which has negative voltage supply on V- for this application?

Thanks, Ian.

  • 0
    TI__Guru 64320 points

    Please see my answers below:

    1. The 0.3V max voltage beyond the supplies specified in the Absolute Maximum Ratings table is due to the ESD reverse-bias protection diodes between the input terminals and each rail - driving the input beyond this limit requires adding properly sized input resistor to limit the input current to 10mA or less. In your specific case, with the input peak voltage up to 700mV beyond the rails, adding 100ohm resistor should prevent damage to LMV641.

    2. Even though LM324A does not show sign of damage, it should be protected with an input resistor to limit the input curret to 1mA or less - see below.

    Exposure of any part to an absolute maximum rated conditions for an extended periods of time may affect device reliability and shorten its life - see below.