I'm building a synchronous buck converter because I can't seem to find a commercial product that fits my requirements. Basically it needs to be able to work over the 2-16V range (4-5A) and be able to switch into bypass mode (100% duty cycle). This is for a battery powered application...so I want the regulator to keep the voltage on the rail at a particular level until the battery discharges under that level...at which point the regulator stops switching and just locks in the on state to allow the rail to follow the battery down. I've found plenty of external mosfet buck converters and gate drivers, but none of them like voltages under 5V or 100% duty cycle.
I've come up with a design (see attached) that I believe should work, but I don't have much experience with designing this sort of thing, so I thought I'd ask the experts. Basically, it is a synchronous buck regulator using two N-channel mosfets. I'm using an MCU to read the output voltage on the rail and drive both mosfets with a PWM signal through a set of transistor-based totem drivers to keep switching speeds up.
My concerns with this arrangement is in the synchronization between the high side and low side mosfet and resulting shoot-through. My original plan was to drive both mosfets with a single pwm output and just use a logic gate to invert the signal going to the low side mosfet, but I'm concerned that the latency introduced by that component will keep the low side mosfet on too long, resulting in shoot-through. With individual control (as I have it setup now), I can make sure that I break-before-make when switching, but I'm worried that might introduce too much latency on the other end and reduce efficiency. Then to top it all off...I do have some doubts about the stability of such a system in general.
So anyway...do I seem to be on the right track, or am I completely out in left field? Any words of wisdom?
I've come up with a design (see attached) that I believe should work, but I don't have much experience with designing this sort of thing, so I thought I'd ask the experts. Basically, it is a synchronous buck regulator using two N-channel mosfets. I'm using an MCU to read the output voltage on the rail and drive both mosfets with a PWM signal through a set of transistor-based totem drivers to keep switching speeds up.
My concerns with this arrangement is in the synchronization between the high side and low side mosfet and resulting shoot-through. My original plan was to drive both mosfets with a single pwm output and just use a logic gate to invert the signal going to the low side mosfet, but I'm concerned that the latency introduced by that component will keep the low side mosfet on too long, resulting in shoot-through. With individual control (as I have it setup now), I can make sure that I break-before-make when switching, but I'm worried that might introduce too much latency on the other end and reduce efficiency. Then to top it all off...I do have some doubts about the stability of such a system in general.
So anyway...do I seem to be on the right track, or am I completely out in left field? Any words of wisdom?
Attachments
-
40.1 KB Views: 85