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TPS61040: TPS61040 second oscillation on SW node before internal MOSFET is on and pull SW to GND

Kevin Wen
Intellectual 2235 points
Part Number: TPS61040
Other Parts Discussed in Thread: TPS61041

Hi team,

We met an issue with TPS61040 that we observe second oscillation on SW node before internal MOSFET is on and pull SW to GND, schematic and measurement as below, would you please show your suggestion? thanks. 

Kevin

TPS61040, blue is the SW waveform. The first oscillation match our EVM user guide that causing by discontinous inductor current, but we don't understand why there is a large ringing after it.

competitor AT1308

Schematic

  • 0
    TI__Mastermind 40080 points

    What is the input voltage, output voltage and output current in this application?

  • 0 in reply to Helen chen
    TI__Intellectual 2235 points
    Hi Helen,
    input voltage is 5V, output voltage is 10.64V, the load is same for TPS61040 and AT1308, customer didn't measure the current, but should be dozens of mA.
    Kevin
  • 0 in reply to Kevin Wen
    TI__Mastermind 40080 points

    AT1308 use PWM control (fixed frequency), while TPS61040 use PFM control. So in the light load conditon, the SW waveform looks like work in skip mode, actually, it works in the PFM mode. turn on serveral cycle, then turn off several cycle.

    You can found the description on the datasheet page 10: " The converter monitors the output voltage, and as soon as the feedback voltage falls below the reference voltage of typically 1.233 V, the internal switch turns on and the current ramps up. The switch turns off as soon as the inductor current reaches the internally set peak current of typically 400 mA (TPS61040) or 250 mA (TPS61041)."