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LMG5200 - Using TI Piccolo for PWM + Reverse Current Capability of GaN MOSFETs inside

Vijay Rajvanshi
Prodigy 50 points
Other Parts Discussed in Thread: LMG5200, TINA-TI

I appreciate any help, as I am an undergraduate student working on a senior design (capstone) project and need a little bit of guidance. The project is the input power conversion system for a high frequency resonant wireless charger to be used to deliver 40-50 W to a standard 12 V U1 lead acid battery on a wheelchair to make charging easier for disabled individuals.

I have a TI Piccolo that I would like to use to drive an H-bridge inverter (consisting of 2 LMG5200s). I've used the LMG5200EVM-01A eval board (http://www.ti.com/lit/ug/snvu461/snvu461.pdf) as a reference in my PCB. There is a full-bridge rectifier in the circuit as well, that I intend on connecting to a 30 V 60 Hz AC input to produce a smooth DC signal for my Vin to the LMG5200.  

In any event, I need to drive the gates for the GaN MOSFETs inside of the LMG5200 with the TI Piccolo that I have. I have ommitted the circuit below from my design and was planning on connecting the PWM inputs from the Arduino directly to the HI and LO pins on the LMG5200. However, I'm not positive about this and want to confirm before I print out the PCB that the connections are correct. How exactly should I connect the TI Piccolo to the LMG5200 in order to successfully drive it? 

Side question:

Since my load is very inductive (essentially a large coil of Litz wire with inductance of >150 uH), I want to ensure the GaN MOSFETs inside of the LMG5200 have a decent reverse current capability. I would prefer not to fry the LMG5200 during deadtime! If this could be confirmed, I would appreciate it. 

input_power_PCB_4.sch

  • 0
    TI__Expert 4640 points

    Hi Vijay,

    thanks for sending us your enquiry. We will be compiling a full answer and get back to you shortly.

    Regards,

    Alberto

  • 0
    TI__Intellectual 2910 points

    Vijay,

    The circuit you have omitted generates a complimentary pair of HI and LI control signals from a single PWM input as well as inserts a dead time to ensure HI and LI are never asserted HIGH at the same time. Removing this circuit is okay, but all the input control and shoot-through prevention will have to be managed in firmware by the Piccolo. Note that in order to allow designers to optimize dead time for their specific applications, the LMG5200 does not implement shoot-through (overlap) protection. Hence, careful consideration must be applied to the control firmware. Also, I recommend that you include the series resistor and cap to GND for HI and LI in case you need any filtering of high-frequency noise.

    Although GaN devices do not have an inherent body diode, reverse current conduction does occur in the form of third quadrant conduction. To answer your second question, yes, the LMG5200 is very robust on this parameter. Figure 3 on the datasheet shows the characteristics.

    I hope this post answers your questions. If it has, please press the “Verify Answer” button below.

    - Daniel

  • 0 in reply to Daniel Ruiz
    Prodigy 50 points
    Thanks for the quick response - this was very helpful. I am operating at very high frequencies (>2 MHz); therefore, the traces from the Piccolo to the HI and LI inputs need to be small to minimize stray inductance and keep added reactance low. Of course, I cannot expect to phase match them, so I would have to do that in firmware by inserting a buffer, most likely. As for the GND, I will connect the Piccolo's GND pin to AGND on the LMG5200 - wanted . If I'm doing anything incorrectly here in terms of connections, kindly let me know.

    One more thing - I wanted to simulate the circuit in TINA TI or PSpice, but it appears the SPICE model available is encrypted. Would it be possible to provide me with an unencrypted model so that I can test the part before I make my purchase later today?
  • 0 in reply to Vijay Rajvanshi
    TI__Intellectual 2910 points

    The planned connections sound good.

    Regarding the model: TI does not offer an unencrypted PSpice model for LMG5200. A request can be made under a signed non-disclosure agreement. However, for your immediate needs, I believe the available TINA model should work. Are you having any issues simulating on TINA spice using the model and or reference design available at http://www.ti.com/product/LMG5200/toolssoftware#simulationmodels?

  • 0 in reply to Daniel Ruiz
    Prodigy 50 points
    Yes - I am completely new to TINA TI and would appreciate any guidance in using it. If there's a link you think might be helpful, let me know.
  • 0 in reply to Vijay Rajvanshi
    TI__Intellectual 2910 points

    I recommend reviewing the TINA-TI Quick Start Guide and any videos from http://www.ti.com/tool/tina-ti#Videos that apply to you. To get started, you can download the LMG5200 TINA-TI Transient Reference Design (Rev. C) available from the LMG5200 device folder. 

    There is also e2e support for TINA-TI if you face any issues specific to the tool: https://e2e.ti.com/support/development_tools/webench_design_center/

    - Daniel