TPS54202: About the switching between PWM mode and Eco-mode operation

Steve Sun

Intellectual 1940 points

Part Number: TPS54202

In the datasheet of TPS54202, as the waveforms shown in Fig8-8, it seems that the IC is operating in PWM mode in first two cycles and then switch to Eco-mode, can make a detail explanation about the three different states of the MOSFETs and how to decide the time of each state. Also, I do not understand the oscillation of the pink waveform.

over 2 years ago

0 Miranda Gu over 2 years ago

TI__Genius 15857 points

Hi Steve,

1. The waveform you shared is in Eco-mode operation. Here the first pulse failed to provide enough power to output, so followed by another pulse to boost Vout. But still it's in Eco-mode. If you capture IL waveform, you could see the IL is discontinuous (DCM mode).

2. The oscillation happened when both FETs off, the residual energy in the L and SW parasitic capacitance drives the ringing that you see.

0 Steve Sun over 2 years ago in reply to Miranda Gu

TI__Intellectual 1940 points

Thanks, but the first and second pulses are 500kHz? and how to decide the start time and end time when both FETs off?

0 Miranda Gu over 2 years ago in reply to Steve Sun

TI__Genius 15857 points

The ringing period is when both FETs off.

0 Steve Sun over 2 years ago in reply to Miranda Gu

TI__Intellectual 1940 points

How long is both the FETs in off state? What determines the end time in this state？

+1 Miranda Gu over 2 years ago in reply to Steve Sun

TI__Genius 15857 points

Hi Steve,

Since the device is not switching, the output voltage will start to decay as energy is drawn from the output capacitors to supply the load current. As the output voltage decreases, the control loop will sense the decreased voltage at FB and restart switching.

+1 Steve Sun over 2 years ago in reply to Miranda Gu

TI__Intellectual 1940 points

Thanks a lot, Miranda.

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TPS54202: About the switching between PWM mode and Eco-mode operation