This anomaly applies to Engineering C, build codes QEAA-BA0, CAAA-BA0, QEAA-BC0.
BUCK changes mode from Hysteretic to PWM or from PWM to hysteretic at a load current that deviates from typical specification. Increased output voltage ripple or increased quiescent current might be seen as a result of this.
BUCK is enabled in AUTO mode. When input voltage is above 4.2 V and output voltage is set below 1.4 V, PWM to Hysteretic transition level has an increased spread. For high input voltages and high output voltages, Hysteretic to PWM transition can happen at a lower load current than expected.
When BUCK is in PWM instead of being in Hysteretic mode, BUCK quiescent current can increase by approximately 4 mA causing lower efficiency at light load currents. When BUCK is toggling between PWM and Hysteretic modes, increased output voltage ripple might be observed.
Force hysteretic or PWM mode through TWI or through a configured GPIO from host software. Choose mode to maximize efficiency.