Converter can be configured under quasi dual phase buck boost operation through MODE pin referring to Table 7-1. The charger operates in buck, buck-boost and boost mode under different VBUS and VSYS combination. The buck-boost can operate seamlessly across the three operation modes. The 6 main switches operating status under continuous conduction mode (CCM) are listed below for reference.

• Buck mode operation: Q4 is constant on and two buck phases should both switching at frequency determined at PWM_FREQ bit. There should be 180 degree interleave between phase A and B to minimize inductor total ripple and finally reduce VBUS and VSYS voltage ripple. Supporting phase shedding feature, converter can automatically transit to phase A single phase operation under light load. The transition threshold is based on SINGLE_DUAL_TRANS_TH bits configuration.
• Buck-boost mode operation: Under quasi dual phase configuration, 2*Fsw switching frequency will be distributed between two buck phases and one boost phase. They should switch in sequence like SW1_A->SW2->SW1_A->SW1_B->SW2-> SW1_B->SW1_A->SW2->SW1_A... equivalent frequency of each phase can be calculated by 2*Fsw/3. For example, when PWM_FREQ=1b (600 kHz), then Phase A, Phase B and boost phase leg will be switching at 400 kHz.
• Boost mode operation: Q1_A and Q1_B should be constant on and the boost half bridge keeps switching at frequency determined at PWM_FREQ bit. Due to two buck phase inductors are in parallel to reduce total inductor current ripple, under boost mode switching frequency is doubled to 2*Fsw (MODE pin configured as quasi dual phase). There could be some CCM/PFM bounce back and force under certain load range( around 2.5A~3A). This bounce will not generate negative input current at input side but could generate some charge current ripple. Once load is higher or lower than this critical range, this issue will disappear.