4.5 A 2-phase resonant switched-capacitor converter delivering 4.3W at 0.6W/mm2 with 85% efficiency

In this work, we present a 2-phase ReSC converter that operates with supply voltages from 3.6 to 6V, providing compatibility for a range of applications including Li-Ion battery supplies. Figure 4.5.2 shows the power train of the 2-phase ReSC converter. The architecture is similar to the 2:1 SC converters in [2-3], but uses inductance, L
_X
, to resonate with the on-chip flying capacitor, C
_X
. On-chip bypass capacitance, C
_bp
, is used to filter the output voltage and complete the resonant loop in the energy transfer process. The timing of key signals in converter operation is shown in Fig. 4.5.3. In normal operation at the fundamental resonant frequency, ω
_o
=(L
_X
C
_X
)
^-1/2
, resonant impedance Z
_X
is configured in parallel with Vin-Vout in φ
₁
; in φ
₂
, Z
_X
is configured in parallel with Vout. If there is a voltage difference between Vin-Vout and Vout-GND, voltage V
_X
appears as a square wave at the resonant frequency. In φ
₁
, a positive half wave current flows into Z
_X
, drawing energy from Vin; in φ
₂
, a negative half wave current flows out of Z
_X
, supplying energy to the load. Similar to the SC topology, this process can be modeled as an effective resistance, REFF, the details of which are discussed in [6]. Operation at the fundamental mode provides the lowest achievable R
_EFF
, which is approximately R
_ESR
·π
²
/8 for the 2:1 configuration, near the minimum achievable R
_EFF
for a comparable SC converter.