Tool/software:
Hello TI community,
I am designing a buck converter using the LM5116MHX/NOPB, targeting a 5V 5A output from a 6–60V DC input. The schematic and PCB layout have been completed, and I am currently facing a major issue during initial testing.
Problem Description:
-
When powered up, HO (high-side gate drive) turns on, causing the input voltage to appear directly at the output, but no buck conversion occurs.
-
The LO (low-side gate drive) remains off and shows no gate voltage, so the low-side MOSFET does not switch at all.
-
No regulated output is achieved, and the output simply tracks the input.
Debugging Actions Taken:
-
Verified component placement and soldering, including MOSFETs and bootstrap components.
-
Checked continuity and voltage levels at EN, UVLO, SS, HO, LO, HB, SW, and VCC pins.
-
Compared my schematic to TI reference designs and evaluation boards.
-
Ensured correct orientation of bootstrap diode and appropriate capacitor values.
Schematic and Images:
-
I have attached the schematic PDF, the KiCad PCB render, and actual assembly photos for reference.
Key Questions:
-
What are possible causes for HO being always on while LO stays off?
-
Which components or pins are most critical in bootstrap operation and gate drive for LO?
-
Are there recommended troubleshooting steps for this situation with LM5116?
-
Any specific advice regarding PCB layout, component values, or signal measurement points?
I appreciate any help or pointers from those familiar with the LM5116’s behavior and troubleshooting.
Thank you!
