LMG1210: Can we use this gate driver for 3-level flying capacitor buck

Hi Jeff,

Thanks for your kind response. But I still have the following concerns.

You have removed VG3 that is driving fly cap. Does it have any interaction with the gate drive output pulses? Moreover, it's not supplying bootstrap VIN_3 (not related with VG3) as there is a diode in reverse direction

In this application, I am operating the converter with duty cycles greater than 0.5, which requires an overlap of high side half-bridge gate pulses. please let me know if this overlap causes any issues.

And each of the half-bridge has its high-side(HO) level shifted but not the low side(LO).   Does it affect the LO of high side half-bridge which is driving MOSFET T2?

Thanks

Hi Srikamnth,

With some further investigation the outputs overlapping is ok. VG3 appears to prevent the top switch from operating.See below image how the bootstrap cap voltage operates with and without VG3.

The purpose of the flying cap is to reduce the inductor ripple current for higher efficiency?

What is the purpose of VG3? in all of the 3level bucks I found I dont see anything driving the flying cap.

For a 3 level buck converter the duty cycle is constantly changing so that the flying cap voltage = VIN/2?

Check out a TI training video I found on 3 level buck that helps with understanding more details about operation.

Thanks,

Hi Jeff,

You are right on the flying capcitor. But the reason that I connected a DC voltage source is to maintain half the input voltage across the capacitor as there is no controller to control the fly cap voltage.( I  have recently started using TINA and it will take signifcant amount of time to implement the control for me)

I tried by removing VG3, and I am able to see all the gate pulses but still the top side devices are not able switch. And also the boot cap voltage acorss the bottom half bridge is increasing more than 5V.

Can you please give me any simulated 3-level fly cap buck converter with with any type of gate driver and switches to speed up our design process.

Thank you

Hi Srikanth,

Thanks for the update, let me look into an existing simulated 3 level buck design with respect to gate drive and input control and update you.

Thanks,

Hi Srikanth,

I just wanted to update you and let you know I found that we have the 3 level battery charger buck device BQ25910. Have you considered this device? What application is this for?

There is however no simulation tool to see control waveforms however the datasheet and product folder contain all theory of operation and design files for getting up and running with a 3L converter using BQ25910. There’s also a webench model for efficiency calculations as well as a excel calculation tool to help make some basic 3L calculations. Let me know if you have any questions from this material so I can further help out with your LMG1210 simulation.

Thanks,

Hi Jeff,

We are planing to desighn for high power and switching frequency. So we can't use BQ2590 for our application.

I am also trying various other Gate driving configurations which I can't share in open forum. One of these configuration have gate pulse coming out from the topside HO but the device is not able to switch.  Can I get direct mode of contact (e-mail) to share my SPICE simulations. Or you can reach out to me at my email:srikanthyerra5@gmail.com

Thanks

Srikanth