SLVSB30B – SEPTEMBER 2011 – REVISED AUGUST 2013
Figure 39. Low Power/Pulse Skipping
During the burst mode, the converter continuously charges up the output capacitor until the output voltage
reaches a certain limit threshold. The operation of the converter in this interval is equivalent to the peak inductor
current mode control. In each switch period, the main switch is turned on until the inductor current reaches the
peak current limit threshold. As the load increases the number of pulses increases to make sure that the output
voltage stays within regulation limits. When the load is very light the low power controller has a zero crossing
detector to allow the low side mosfet to operate even in light load conditions. The transistor is not disabled at
light loads. A zero crossing detection circuit will disable it when inductor current reverses. During the whole
process the body diode does not conduct but is used as blocking diode only.
During the skipping interval, the upper and lower transistors are turned off and the converter stays in idle mode.
The output capacitors are discharged by the load current until the moment when the output voltage drops to a
The choice of output filter will influence the performance of the low power circuit. The maximum ripple during low
power mode can be calculated as:
Where KRIP is 1.4 for Buck1 and 0.7 for Buck2 and Buck3. TS can be calculated as:
TS = éæ VIN -VOUT ö VOUT ù
The total power dissipation inside TPS652510 should not to exceed the maximum allowable junction temperature
of 125°C. The maximum allowable power dissipation is a function of the thermal resistance of the package (RJA)
and ambient temperature. To calculate the temperature inside the device under continuous loading use the
1. Define the set voltage for each converter.
2. Define the continuous loading on each converter. Make sure do not exceed the converter maximum loading.
3. Determine from the graphs below the expected losses in watts per converter inside the device. The losses
depend on the input supply, the selected switching frequency, the output voltage and the converter chosen.
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