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LMG1210: use LMG1210 with large device at high frequency

Shengnan Li
Expert 1010 points
Part Number: LMG1210

The eval board of LMG1210 has EPC2001C and can switch up to 15MHz. Our design use EPC2055 and EPC2023 as upper and lower fets. EPC2023 has significantly higher gate charge. we want to switch at 10MHz. Do you think LMG able to drive that fast? if not, can we add heatsink?

Regards,

Shengnan

  • 0
    TI__Genius 14145 points

    Hey Shengnan,

    Thank you for your question regarding the LMG1210.

    For determining the maximum gate driver frequency, you can utilize this tool:

    [FAQ] UCC27282: How to Calculate the Max Operating Frequency of a Half-bridge Gate Driver

    Based on some assumptions and a rough calculation, your operating conditions seem to be in line with where this driver can operate. It would be best to put your operating conditions into this tool to check and be sure.

    There are times where heat sinks are used for these drivers but in this case that doesn't seem necessary.

    Let me know if there are any further questions.

    Thank you,

    William Moore

  • 0 in reply to William Moore
    Expert 1010 points

    Hi, Wiliam,

    I tried the tool, with example of LMG1210 demo board, it shows this demo board can run at 70MHz, actually this demo board specifies 15MHz maximum, when i ran it, it shut down around 13MHz. Can you go though it and check where is the discrepancy come from? 

    https://www.ti.com/tool/LMG1210EVM-012

  • 0 in reply to Shengnan Li
    TI__Genius 14145 points

    Hey Shengnan,

    For your calculation, IVDD, IHB and IHBS are not the same as the datasheet. With that change, you get to around 52MHz from the calculator tool. As a reminder, this calculator tool is just a guideline to get you in the right direction and ball park of where you need to be and is giving the maximum frequency calculation.

    As for the shut down state that you saw with the EVM, from Table 1 of the user's guide, note 1 states "Using EPC2001 relatively large FETs limits the usable maximum frequency, smaller FETs allow operations up to 50MHz.

    What occurred when you went into shut down at 13MHz? Did the FETs fail? Did the driver fail?

    The test waveforms in Section 8.2 of the User's Guide show up to 10 MHz operation data.

    The maximum frequency that you can operate is not just a limitation of the driver but also of the other components in the circuit such as the FETs.

    Let me know if you have any further questions.

    Thank you,

    William Moore

  • 0 in reply to William Moore
    Expert 1010 points

    Hi, William,

    When running LMG1210 EVM, it shuts done beyond 13MHz, because of overtemperature protection of LMG1210. Nothing destructive.

    I understand that FET Qg plays a major rule, Qg higher, fsw is lower. That is why i want to use the EVM board to validate the calculation tool. However, there is a big discrepancy between them.

    Regards,

    Shengnan 

  • +1 in reply to Shengnan Li
    TI__Genius 14145 points

    Hey Shengnan,

    As a reminder the calculation tool is just a guideline.

    Are you following the maximum frequency testing set forth by the EVM's Users Guide? This is located in Section 7.3.2.1 Maximum Frequency of the LMG1210EVM User's Guide.

    The limit to frequency is based on the current in the LDO and FET behavior. So, depending on your setup, you may be stressing or violating the setup's operating conditions for running at these high frequencies.

    Let me know if you have any further questions.

    Thank you,

    William Moore