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LM4950 blew up when both outputs shorted to Ground.

Other Parts Discussed in Thread: LM4950

We using TI LM4950 in our production and we fail average 1 a month in production area due to the output cable shorted to ground this case both output short to ground at the same time and the LM4950 Blew.

 

Reviewing the TI spec sheet on LM4950 says short circuit protection; The LM4950 features an internal thermal shutdown protection mechanism along with short circuit protection.

 

I did some experiments:

Ground one side of the output of LM4950 OK

Ground one side of the output and ground the other to ground of LM4950 OK

Ground both sides of the LM4950 at the same time and tie ground the LM4950 Blew

It looks like the LM4950 does not have a good output protection to ground

 

I try PTC at the output to protect the LM4950, the problem is the nature of PTC is response to slow and will not have enough time to protect the LM4950.

 

Any advice or guidance to protect the LM4950 would be greatly appreciated.

  • Hi Ban,

    My colleague will work with you on this. He will get back to you as soon as he's back to office.

    reg,

    Paul.

     

  • Hi Ban,

    I have contacted some expert for this issue.  It is very likely that I can offer you some answer tomorrow.

    Andy

  • Thank You Andy,
     
     
     
    Ban Tien Dinh
    Senior Research & Development Engineer
    3000 Minuteman Rd M/S 105
    Andover, MA 01810-1099.
    Phone: 978-659-2427
    FAX: 978-687-7265
     
     
    From: Andy Liu SH [mailto:bounce-1864278@mail.e2e.ti.com]
    Sent: Tuesday, November 04, 2014 12:17 PM
    To: AudioAmpsForum@mail.e2e.ti.com
    Subject: RE: [Audio Amplifiers Forum] LM4950 blew up when both outputs shorted to Ground.
     

    Hi Ban,

    I have contacted some expert for this issue.  It is very likely that I can offer you some answer tomorrow.

    Andy

  • Hi Ban,

    Here is some comment from my colleague:

    This is very tough issue. Yes, LM4950 has protection function with both output current limit and thermal shutdown.

    However, if both outputs are shorted at the same time, each output current will be over 5 Amps flow

    and then with some delay time thermal shutdown will start working but before thermal shutdown works,

    the device will have damage. I don’t know the Vdd value though if Vdd=12V, the device will consume

    more than 120W. I don’t have good solution to protect the device in outputs shorted to GND at the same time though

    by adding small resistor in series to the load or quick cut fuse on the supply line.

    I hope his comment could you help you a bit.

    Andy