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LM4766: Voltage at Metal Tab

Part Number: LM4766
Other Parts Discussed in Thread: TPA3116D2

Hi Team,

Could you please tell me the voltage of non-isolated TO-220's metal tab? 

  • Hi

    The tab should be connected to heat-sink.

    Regards,

    Derek

  • Hi Yanming, 

     Thank  you for reply. The voltage of non-isolated TO-220's metal tab is GND. Is my understanding right?

    Best Regards,

    Taito Takemura

  • Hi Taito

       Yes, you are correct.

  • Hi Shadow,

    I have ab additional question about GND of LM4766. Could you please answer it?

    The datasheet says LM4766 has two GND (GND A and GND B).

    - Are GND A and GND B electrically separated?
    - If so, how is the voltage of the metal tab related to the voltage of A and the voltage of B? Should I think the voltage of metal tab is GND A, GND B or other?

    Thank you for your help.

    Taito Takemura

  • Hi Taito,

    GND_A and GND_B should be connected together, do not separate the ground.

    Regards,

    Derek

  • Hi Support Team,

    Could you please tell me what to think about the voltage of the metal tab after all? According to customer's measurement, there is a big resistance between GNDA, GNDB and Metal Tab. This seems to be inconsistent with the previous answer.

    [Customer's Measurement]

    When the customer measured the resistance value between each point of LM4766 with a tester,

    Resistance between metal tab and GND A: 1 MΩ
    Resistance between metal tab and GND B: 1 MΩ
    Resistance between GND A and GND B: 1.5 MΩ
    It is unlikely that GND A, GND B and metal tab will all have the same potential.

    By the way, the resistance between the metal tab and Vee is 1 Ω by their measurement, so isn't the metal tab connected to Vee?

    It would be helpful if you have an image showing how GNDA, GNDB, Metal tab, and Vee are electrically connected.

  • Hi Taito,

    GNN_A, GND_B and VEE connection can be referred Figure 2. Typical Audio Amplifier Application Circuit in datasheet. 

    GNN_A, GND_B are two channels ground pins. We suggest the ground pins should be connected together.

    I'm currently trying to get information about the internal connection of the pad. LM4766 is very old device, why don't customers try our class-d device(e.g TPA3116D2)?

    I asked if the heat sink is only connected to the IC's or connected somewhere else, like GND, because if it is connected only to the IC's then it could be fine if the pad is internally connected to, lets say, GND or VEE. However I did not device on hands. And I did not deep out more information.

    If you customers checked and confirmed that the pad is connected to VEE. I think it is so.

    Regards,

    Derek

  • Hi Derk,

    Thank you for your prompt answer.  I'm looking forward to information about the internal connection of the pad.

    Could you please me confirm is my thoughts are correct?

    - "GNN_A, GND_B are two channels ground pins. We suggest the ground pins should be connected"

     => GND A and GND B aren't connected in IC and the user should connect them electronically using an external  line outside the IC.

    - "If you customers checked and confirmed that the pad is connected to VEE. I think it is so."

     => This means Vee is connected to metal tab electronically in IC. Or  this means Vee is connected to metal tab electronically in customer's test environment?

    Best Regards,

    Taito Takmemura

  • Hi Taito,

    GND_A and GND_B should be connected to audio input ground. 

    For Q2, I think so, if pad connected to VEE internal according to customer test.

    And I do suggest they can use new generation Class-D device for new projects. Then they can get more and efficient support.

    Regards,

    Derek  

  • Hi Yanming,

    Thank you for your comment.

    I suggested to the customer to replace the LM4766 with a new product. It cannot be easily migrated to a new product because the LM4766 has been used for 10 years and is a part that greatly affects the equipment performance. Additionally because it is not for audio use, they can use two power amplifiers in stead of LM4766. Could you please let me know if you know new devices which can replace LM4766 in power amps?

    How about  information about the internal connection of the pad?

    Best Regards,

    Taito Takemura

  • Additional Supplement :

    Because the customer floats the device in the air when they measure the resistance between Vee and GND, a short circuit between Vee and GND  in the customer's environment will be unthinkable. Could you please measure the resistance between Vee and GND once in your environment?

    Best Regards,

    Taito Takemura

  • Hi Taito,

    I am sorry that I do not have the samples in hands.

    The new device TPA3116D2 is suitable. 

    I believe customer measurement that VEE and pad are internal connected. So I think they should follow it.

    Regards,

    Derek