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TPS54227: 2A Sync SMPS: Inductor Current Waveform

ikon
Genius 5355 points
Part Number: TPS54227

Hi Support,

Am loading the IC 20% and 90% and noting down the current I (inductor current) at the point shown below.
The full load will be around 1.2A
Inductor used is Sumida 4.7uH (6030CDC4R7)
The waveforms are enclosed.
Am using a Lecroy scope with a Lecroy current probe.
Found the current ramp going below zero.

Questions:
1. Is it normal for the inductor current to go below zero.
2. Am I doing some thing wrong while taking the measurement. The rms value matches the load applied( I am using a electronic load( HP meter).
3. Does it mean we need to change any component value?

Need your help to analyse the wave form.
The blue trace is the voltage at the SW output, the yellow trace is the current.

Thanks.

  • 0
    TI__Mastermind 18510 points

    Hi ikon,

    The chip should work at FCCM mode, please refer to 7.4 page10 in DS.
     At this mode, low-side mos is always on, when Vout is light loading(your first picture test), the current from output cap will go reverse through L and low-side Mosfet to ground, not to the output, and that will cause the nagative inductor current, so this is normal action.

    BR,
    Yuchang