TPS62260 SW switching waveform

Q: TPS62260 SW switching waveform by 318382

Our customer asks about the SW swtiching voltage looks exceed the ABS MAX voltage -0.3V. The attachment shows the evaluation result of both customer's board and TI EVM. Both of the SW wave form shows that SW voltage is down to -0.7V in larger than 100mA load condition due to turning off high side and low side FET at tthe switching cycle. Does it make a reliability problem on SW node due to functioning by exceeding ABS MAX -0.3V condition.


A: Re: TPS62260 SW switching waveform by 10449

The negative voltage on the SW node is caused by the current flowing from ground into the TPS62260 synchronous rectifier and out of the SW pin to the inductor.  The current flows through this path after the power FET turns off.  After the power FET turns off and before the synchronous FET turns on, the current flows through the TPS62260 synchronous FET's parasitic diode.  This normal and expected and will not damage the IC.  This negative voltage spike is present on all synchronous buck converters from TI and all other companies and is not a problem.

Note the voltage spike in the light load condition.  This is caused by the inductor current flowing into the SW node and through the power FET's diode to Vin.  This is also expected.  The voltage on the SW node in this condition should be kept below the abs max of 7V to avoid damaging the synchronous FET.