I have designed a synchronous buck converter to step down a 17.4V voltage source to 12V at the output. I have attached the schematic as shown. Problem: The Buck is not operating as expected at all. Here are the measurements I was able to get from testing it:
- PWM frequency: 62.5kHz
- Vg of M1 = 8.5V
- Vds = 0.03V
- VL (Voltage drop across inductor) = 17.37V
- Vload {Voltage at the load) = 0V
First off, I cannot understand why I am only getting 8.5V to the gate of M1. I am using a half bridge gate driver with bootstrap topology, but yet the voltage I am getting out of the HIGH pin of the driver is just the 8.5V. And not to mention the fact that I am even getting a significant voltage drop across the inductor. I can't understand why that is so at all. I am thinking that the buck may be operating in DCM which may explain it, but I'm not so sure. Could anyone help me make sense of what could be wrong here?
P.S.(I have attached a copy of the datasheet of the gate driver showing how I have hooked it up. See page 2) DRV_HI pin feeds into the gate of M1, and DRV_LO pin feeds into M2. C4 and C3 are both 0.1uF ceramic capacitors. Vcc is 11V, and Vin from the microcontroller is roughly 5V
I apologize, here is the URL for the sheet: http://www.onsemi.com/pub_link/Collateral/NCP5111-D.PDF
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