Hi Experts,
My customer reported a start up problem with TPS54310 circuit. The problem is the dcdc circuit cannot start up with a 2ohm of load, while it can start up properly with 4ohm load. Here is the schematic:
In which, VCC=5V, VOUIT=3.3V, Inductor is 2.2uH with rated current of 4Arms (4.8A sat).
The ckt cannot start up with 2 ohm of load, the output voltage is very low, almost zero. Vbias is correct, arround 2.7V. The SS pin voltage seems not correct. With a ss cap on ss pin, the ss voltage is very low, arround 1V. I have engineer removed ss cap and observe the waveform on ss pin, below is the ss waveform:
It seems the ss is periodically discharged by internal ckt. This is the reason why the ckt cannot startup. But i do not understand why this pin is periodically discharged? I have engineer observe the VIN voltage, it is very stable 5V, no significant drop. And the temperature of the device is low, arround 30C. Is there any other possible reason that result ss discharged?
Thank you!
John
