Datasheet

Switching Waveforms
2-7
Setup and Test Results
2.6 Switching Waveforms
Figure 2−3 shows the switching waveform at the SW pin of the TPS61040.
When the internal FET turns on, the voltage at the SW pin is pulled to ground
until the inductor current reaches 400 mA. When the inductor current reaches
400 mA, the FET turns off and the voltage at the SW pin rises to the output
voltage plus the forward voltage drop of the diode. During this time, the
inductor transfers its stored energy to the load and the output capacitor. When
the inductor current decays to zero, the SW node rings at a frequency
determined by the output inductor and the drain capacitance of the internal
FET. This ringing indicates a discontinuous boost power supply topology, and
confirms that the inductor current has gone discontinuous.
Figure 2−3. SW Waveform
1
1 µs
0.5 V
0.2 V
0.1 V
10 mV
2
3
4
1
RIS BWL
DC x10
DC x10
DC
DC
1 DC 11.3 V
400 MS/s
AUTO
1 µs
5 V