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I am designing a power supply with an adjustable output voltage from 5.4V to 50.4V. The LM5176-based buck-boost converter should start in boost mode regulating to 50.4V. But right after turning on the input voltage it just ramps-up to the desired output voltage and then goes off and never works again. When setting the output voltage to the 43V (removing resistor between feedback and output of the DAC), the controller works fine. The device is run at the input voltage of 32V and with no load at the output. The schematic of the device:
The layout of the device:
After using TI webench tool, I tuned the COMP and SLOPE components only for boost mode. The results where the same. I did sampled Vout (channel C1), COMP pin (channel C2) and FB pin (channel C3).
The first picture shows when Vout is set to 43V, it ramps up and regulates as desired:
And the following pictures show the failing of the LM5176 to regulate to 50.6V after ramp-up: