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LMG3410: Design Issues

Efi Ovadia48
Intellectual 285 points

Part Number: LMG3410

Hello,

I have a few questions regarding the LMG3410:

  1. The current data sheet have only typical values for most cases - how can I get the MIN,MAX values? especially for tpd,on     tdelay,on     trise      tpd,off      tfall
  2. I'm using the LMG3410-HB-EVM & LMG34XX-BB-EVM for evaluating the model - If I will create a situation where a shoot-through happens, will the LMG3410 protect itself, or it will burned out?
  3. Can you say what is the timing loss when I use a bootstrap diode for the 12V VDD? I have a 12V input voltage and I prefer using an isolated voltage for VDD - can you recommend on a specific design or part for this issue?
  4. What is the maximum current drawn from the VDD supply?  the typical shown as 43mA.
  5. My main goal is to build a H-bridge topology (with 4 LMG3410) with 200V input voltage with the highest frequency - I'm aiming towards 1MHz. Is it possible for this ic? do you have a H-bridge design example?

Thank you very much,

  • 0
    TI__Intellectual 805 points
    Hello,
    I'll try to help you out with your questions.
    1. This is true because these are all dependent on the operating conditions like Vbus, Iload, and RDRV value (gate current). The devices are tested under certain operating conditions. If you can give me your exact dv/dt (or RDRV), Iload and Vbus, I may be able to help you with the expected delays in the system.
    2. Even though the protection in LMG3410 is intended for over-current protection, it is likely that it can protect the device in case of shoot-through condition due to fast response. In our tests on a couple of samples at room temperature, the devices survived in a shoot-through event.
    3. Please check the HB design file from the link below. It uses isolated supplies from 5V to 12V generated for both low and high side GaNs. It also has footprint for bootstrap diode and resistor. The important parameter is the primary to secondary parasitic capacitance. You will need a very small parasitic capacitance such as the part used in the HB EVM.
    www.ti.com/.../LMG3410-HB-EVM
    4. With process variations into account, max driver current would not exceed 47mA at 1MHz switching.
    5. We will have a full-bridge EVM designed and released to ti.com in about 2 months. Please check back later for this design. When you design your board, I highly recommend you follow the design steps given in
    www.ti.com/.../snoa946.pdf
    LMG3410 can switch at 1MHz. There is no problem with that.

    Regards,
    Serkan
  • 0 in reply to Serkan Dusmez
    Intellectual 285 points

    Hi,

    Thank you for your response,

    1. For our application: Vbus = 200V, ILoad = 12A, RDRV -> 100V/ns
    2. ok
    3. If I use the recommended bootstrap diode, what will be be timing effect on the circuit ? there is a 2ms delay for Tstart - startup time of the switcher, so the capacitor will hold that voltage, right? I don't have 5V input, only 12V - do you have an isolator topology from 12V to 12V?
    4. ok
    5. ok

    Thank you,

  • 0 in reply to Efi Ovadia48
    TI__Intellectual 805 points
    Hello,
    For item 3: In case you prefer using bootstrap diode; 2ms start-up time is from VIN passing UVLO (9.4V max) under given VNeg and 5VLDO capacitors in the datasheet. You will have this for your low side GaN first. Then, to charge the high side GaN capacitor you need to turn on low side GaN in a buck configuration till high side is fully biased or PWM low side GaN in a boost type configuration. On top of that 2ms, there will be some time required to charge your VIN capacitor. You can find this time for your design by calculating from t=C*9.4V (UVLO max)/I. Same thing goes for high side GaN FET. The limitation of bootstrap supply comes from the min on-time for low side GaN. Based on your design at 1MHz, you need to have sufficient charge for your high side bias supply in every cycle, that means low side GaN has to be on for a min amount of time.
    If you prefer to use isolated supply, TI does not have push pull transformer driver that works with 12V input, to my knowledge. I would recommend using a switching voltage regulator to drop 12V to 5V, as you will need a 5V in your design to power the primary side of digital isolator. Then you can use the same config as in the HB-EVM design.
    I don't recommend typical isolated power supplies (integrated switch + transformer), as these typically have primary to secondary capacitance around 40-50pF.
    For item 1: I will come back with results tomorrow.
    Regards,
    Serkan
  • 0 in reply to Serkan Dusmez
    Intellectual 285 points

    Hi Serkan,

    Thanks again for your detailed answer - waiting for the timing results :)

    I have two more questions:

    1. If I work with switching of 1MHz, what is the minimum duty cycle the LMG3410 can handle?
    2. Can I use ISO7831FDWR digital isolator with 3.3V input and 5V output? The data sheet shows parameters only for equal VCCs, although it states 2.25 V to 5.5 V Level Translation capability.

    Efi

  • 0 in reply to Efi Ovadia48
    TI__Intellectual 805 points
    Hi Efi,
    For your operating conditions, the total turn on delay should be around 24.7ns and total turn-off delay is 29ns. I guess that this closes your earlier question.

    1. LMG3410's min on time is about 10ns. This means that if you give 10ns of input signal under RDRV=15kOhm, the switch node will make 50% transition. This corresponds to 1% duty cycle at 1MHz.
    2. Yes, 3.3V on primary and 5V on secondary is possible.

    Hope these resolve your questions.
    Regards,
    Serkan