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LM2904: about LM2904 output short to GND

Vera Mao
Expert 5065 points
Part Number: LM2904
Other Parts Discussed in Thread: LM358

hi dear supporting team,

customer is using LM2904, there is one application which connect MOS  at the output, when it need protect, there will be a drive signal cause 2904 output short to GND. is it ok? tks!

  • 0
    Guru 140200 points
    Hi Vera,

    the short circuit current of LM2904 is up to 60mA. So, I wouldn't clamp the output voltage wihtout having a current limiting resistor between the output of LM2904 and clamp transistor.

    Kai
  • 0 in reply to kai klaas69
    TI__Expert 5065 points

    Hi Kai,

    the power supply is 12V and GND.  So do you mean the circuit is ok without having the resistor?  i.e. if put a clamp resistor btw 2904 and the transistor, it may cause very high voltage at the output, correct? So for the circuit customer designed, it will not damage our chip? BTW, there is internal current limiting circuit which limit the short current to 60mA, right?   tks!

  • 0 in reply to Vera Mao
    Guru 140200 points

    Hi Vera,

    the first plot shows that the output of OPAmp is short circuited by your method. The second plot shows the usual method of clamping the output voltage of an OPAmp by inserting a suited current limiting resistor.

    vera.TSC

    Kai

  • 0 in reply to kai klaas69
    TI__Guru*** 145176 points
    Vera,

    Kia's series resistor suggestion is prefered. The LM358 does have current limiting however the current limit is designed to protect against fault conditions like accidental shorts. In current limit mode the LM358 see a lot stress. The series resistor reduces the total stress and the resistor shares the stress. "Stress" is power dissipation which is voltage * current. More resistance lowers current so less stress. Moving the voltage drop to the resistor moves most of the stress to the resistor. Size the resistor power rating based on maximum power possible (12V - 1.5V)^2/R