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LM5122-Q1: Can this IC operate with 5V steady state VCC voltage?

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Replies: 5

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Part Number: LM5122-Q1

Hello,

Can this IC operate with 5V Steady state VCC voltage? The purpose is using this IC directly driving GaN FETs.

Is VIN pin allowed not to connect to the real input voltage but connect together with the VCC Pin to an external 5V or 5.5V VCC voltage? 

Thank you very much.

Best Regards

Jieyi Zhu

  • Hi Jieyi,

    VIN pin is used as the input to the internal VCC regulator. It can be connected to a voltage higher than what the VCC regulator will output, which is part of the intended operation.

    The other outcome is powering VCC from a voltage in between 9V - 14.5V in series with a diode, with a blocking diode in series from the VIN supply to VIN pin.

    For your case, I would not recommend shorting VIN and VCC together. 

    Thanks,

    Richard

  • In reply to Richard Fu22:

    Hi Richard,

    Thank you for your answer. 

    I understand the function of the VIN pin. When I use external VCC supply only, is actually VIN pin not really necessary.

    And I also don't want let it Floating. That's why I would like to short it to VCC pin. 

    In this way, can I just externally supply 5V/ 5.5V DC voltage to VCC Pin? Would this IC operate correctly? 

    Thank you.

    BR

    Jieyi

  • In reply to Jieyi Zhu:

    Hi Jieyi,

    In order to disable the internal regulator, you must supply a voltage higher than VCC regulation target (9V<VCC_ext<14.5V)

    In your case, you cannot supply external 5V/5.5V DC voltage to VCC pin this way. 

    Please see section 7.3.2 and figure 17, 18, and 19 in LM5122 datasheet for more clarification.  

    Thanks,

    Richard

  • In reply to Richard Fu22:

    Hi Richard,

    Is there any way to supply this IC with 5V VCC?

    Thank you.

    BR

    Jieyi

  • In reply to Jieyi Zhu:

    HI Jieyi,

    With the LM5122 as it is, you can control the VCC voltage to get 5V using a clamp circuit at the input, but you cannot control the output of the VCC regulator in terms of spikes, etc... Therefore, it is not beneficial to control VCC output to achieve your goal.

    In this case, what I would recommend is to use the gate output of the LM5122 as the control signal for the LM5114, a low-side GaN Driver. http://www.ti.com/lit/ds/symlink/lm5114.pdf?ts=1588785584829

    Thanks,

    Richard

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