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LM675:Short-circuit fault between Vcc and VEE

Hideto Yamamoto
Prodigy 60 points
Part Number: LM675

Tool/software:

Dear Technical Support Team,

We are currently using the LM675T/LF02 on one of our boards.
Recently, we encountered a failure in which the supply  (Vcc to −VEE) became shorted within the LM675T/LF02.

Our initial assumption is that through-current may have occurred between the high-side and low-side transistors in the output stage.

However, while investigating the cause of failure in the driver section, we have not been able to identify any external factors that might have triggered the issue.

For reference, the supply voltages in our application are +33 V and −24 V.

Could you kindly advise what potential causes may lead to such a failure in the LM675T/LF02? Any guidance on possible mechanisms or conditions that could result in this type of short circuit would be greatly appreciated.

Sincerely,

  • 0
    TI__Genius 14926 points

    Hello Yamamoto-san,

    Your thinking is typically correct, shorts between VCC and VEE typically occur due to output stage damage creating a low resistance path to form. 

    The most common way we can see this damage occur is through Electrical Overstress (EOS).

    This can appear as the output being forced to a potential or excessive current flow which causes damage to the output stage. 

    In the case of power amplifiers, we have a similar EOS type requirement being the SOA curve. The device will often try to maintain operation within the SOA curve, but large transients or reactive loading effects can cause the amplifier to exit safe operating area for enough time to cause damage. Generally when driving reactive loads, we recommend placing external current steering diodes to help prevent EOS events. 

    What is the LM675 connected to? Is this the only unit which has failed?

    +33V and -24V is perfectly valid for the operation of the device. 

    If you have a curve tracer, you could look at the output stage transistors relative to the supply rail. I would imagine these will be shorted like you mention. 

    Do you have a schematic I could look at? 

    Thanks,

    Jacob

  • 0 in reply to Jacob Nogaj
    Prodigy 60 points

    Hello Mr. Jacob Nogaj,

    A polyswitch has been placed at the output to provide a current limit of 100 mA.
    In addition, although there are ten identical circuits using the LM675, only this particular IC has failed.

    Please find attached the surrounding circuit of the LM675 for your reference.

    Please let us know if you also require the surrounding amplifier circuitry.

    Sincerely,