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LM1875: About internal output protection diodes

Tao_2199
Genius 5660 points
Part Number: LM1875

Hello,

 

Regarding to internal output protection diodes on LM1875, my customer is asking some question.

They are using for coil driver and their conditions are following.

･Load : Induction load (linear reactive loads)

･Input : Tens of KHz sine signal (AC)

･Output: The input is amplified with the amplitude of the power supply voltage(±30V).

(Question)

 

(1) In case of linear reactive loads, the output clump is protected by internal output protection diodes.

I am understanding above from datasheet page 7. My understanding is correct?

If so, how many volts can it protect(clump) up to?

And how long can it continue to protect(clump) ?

 

(2)They have a concern of surge(EOS) on output.

I’m not sure it is by reactive loads or power supply, and I think external surge protector is needed.

Could you please give any advice or comment? (They image impulse surge.)

 

Regards,

Tao_2199

 

  • 0
    Genius 5660 points

    Hello,

    Additional question,
    (3) When Vcc=0 and no input, there is possibility AC current inputs to output.
    In this case, is there any impact on device?
    I think this device isn’t output tolerant because of internal output protection diodes.

    Regards,
    Tao_2199

  • 0 in reply to Tao_2199
    TI__Mastermind 19030 points

    Hi Tao,

    Please see my comments.

    1) Yes, output clump is protected by internal output protection diodes. The protection mechanism is to check the current through the output to device. The LM1875  limits current to around 4A, while the maximum current passed by the output devices is usually limited by internal circuitry to some fixed value.

    2) Usually customers add TVS diode on output for surge protection. 

    3) Vcc=0 and no input inducing noise, there is no current inputs to output.

  • 0 in reply to Yanming Gong
    Genius 5660 points

    Hello Yanming,

     

    Thank you for comment.

    I have additional question.

    (4) Do you have a data of maximin protection voltage on internal output protection diodes protect?

    (Up to absolute supply voltage(60V)?)

     

    (5)About (3) question,

    When Vcc=0, there is possibility the back current will flow from load to output.

    In this case, is there any impact on device?

    If so, where is protection device needed to place?

    And what kind of device will be used for protection?

     

    Regards,

    Tao_2199

  • 0 in reply to Tao_2199
    TI__Mastermind 19030 points

    Hi Tao,

    Please see my comments.

    4)  60V is the max voltage value that device can work well including play. The max protection voltage is more high than this level. For more high voltage level, device will be shutdown for protection, and device can not be destroyed.  

    5)  It depends on time and magnitude of the back current. I think LM1875 has reverse protection for high back current, for example output short to power. 

    But LM1875 is very old device, I want to deep in to find the related data, but I did not find the data. I am sorry for that.

    Could you please tell me what's your application? I think we can recommend our new devices, so that you can get more support.

    Regards,

    Derek