Hello, I have a design in production I am seeing problems with, input voltage is 5.0V and output voltage is 3.3V.
Trying to operate in low noise mode, by holding the sync input to high to force fixed frequency PWM mode. Most devices operate at a fixed frequency of approx 800-900kHz.
Some devices operate at a much lower 80-90kHz which makes me think they are operating in the power-saving pulse frequency modulation (PFM).
Spraying the device with a small amount freeze spray will cause it to move to the 800-900kHz range.
I have attached scope screen shots of the SW pin on channel one, and the SYNC input on channel two.
This first one shows the typical faulty mode of operation:
This second one shows the device working as expected:
The problem is, when the converter operates in the 80-90kHz mode, the product doesn't work due to excessive noise on the 3.3V rail.
Here is the schematic, I know there is a resistor and capacitor on the LBI input that doesn't make sense, but this should not cause any problems.
I have replaced the failing designs with known sourced ICs from Mouser, but they can still show the same problem after replacement.
