Step-down switching regulator with 1MHz PWM. Schematic question.

[baev_al]

Hi.

Any ideas on the below task will be appreciated.

I need to achieve step-down switching regulator with the following output parameters: I max = 8A , V max = 8V. I managed to do this with PWM frequency equal to 100kHz. But I need to reduce component sizes so I want to run it with 1MHz. However even with 2A load output MOSFET (IRF540) and driver (ZXGD3004E6) are too hot. I think that control signal is not fast enough. Is it possible to make the slopes sharper?

Below are schematic and oscillogram. Yellow one is PWM on Gate pin of IRF540 (600kHz duty cycle = 50%), blue one – output voltage. With this setup output current was 1.2A.

Real schematic is built on the development board, so design is definitely not perfect, however moving components around and changing wire lengths did not change the control signal significantly.

PWM is generated by FPGA (so I can control frequency and duty cycle easily).

Thanks.

 

[ronsimpson]

R1 750 ohms change to 1/2 or near 400 ohms and see if the gate drive has sharper edges.
I think 1mhz is fast for the MOSFET.

 

[baev_al]

I tried to reduce R1 resistor - the control signal did not changed. Actually I already reduced it several times (I started from 2k). And speaking about frequency of MOSFET control - there are MOSFET drivers working with 2MHz PWMs, such as TI TPS28225... But HOW do they drive the MOSFETs...