SLVSET3D March 2020 – October 2020 TPS63900
Figure 7-1 shows a simplified block diagram of the power stage of the device. Inductor current is sensed in series with Q1 (the peak current) and Q4 (the valley current).
The device uses a trapezoidal inductor current to regulate its output under all operating conditions. Thus, the device only has one operating mode and does not display any of the mode-change transients or unpredictable switching displayed by many other buck-boost devices.
There are four phases of operation:
Figure 7-2 through Figure 7-4 show the typical waveforms during continuous conduction mode (CCM) switching for three operating conditions. During discontinuous conduction mode (DCM), the typical inductor current waveforms look similar to CCM with Phase D at 0 A inductor current. In deep boost mode, where VI << VO, Phase C length gradually decreases to zero until the switching waveform becomes triangular.
The ideal relationship between VI and VO (that is, assuming no losses) is
By varying relative duration of each phase, the device can regulate VO to be less than, equal to, or greater than VI.