Supplement: Power
Figure 12. Reversed – VOUT waveforms during start-up: (a) relatively small CIN (50μF) com- pared to COUT (330μF) and (b) relatively large CIN (350μF) compared to COUT (330μF).
Figure 8. Example circuit of an inverting configuration.
Figure 9. Bench tested efficiency curves for –12VOUT.
Figure 10. Charging current flow paths dur- ing start-up.
However, an inherent clamping circuit is present inside of the µModule regulator, as shown in Figure 11. VSD3 and VSD4 represent the source-to-drain voltages of M3 and M4, respectively. When –VOUT > VSD3 + VSD4, the body diodes of M3 and M4 conduct, taking over the charging current. These two body diodes create a natural clamping circuit. In other words, the maximum reverse output voltage is VSD3 + VSD4.
Figure 11. The natural clamping circuit in the four-switch buck-boost.
Figure 12 displays the bench-tested reversed output voltage waveforms during start-up. In Figure 12a, the magnitude of reversed -VOUT is approximately +0.75V, with a limited CIN (50µF) presented in the circuit compared to COUT (330µF). When increasing CIN to 350µF, a higher reserved –VOUT of +1.5V is observed, as shown in Figure 12b.
zero during start-up. This same behaviour is observed when configuring the four-switch buck-boost regulator in inverting mode. Figure 10 illustrates the mechanism behind the reversal of the output voltage during start-up. When the input supply is turned on, but before all four MOSFETs begin
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switching, the input current starts charging the output capacitor in reverse through two paths: via the CIN decoupling capacitors placed across M1 and M2, and through the INTVCC capacitor path. If CIN or CINTVcc are significantly larger than COUT, a higher reverse output voltage is likely to occur.
The ratio of CIN to COUT can be adjusted to minimise the positive output voltage. A smaller ratio results in a lower positive output voltage before reaching the internal clamping voltage, Vsd3 + Vsd4. Additionally, an external low forward drop clamping Schottky diode can be added at the output to limit the positive voltage to a desired level, as shown in Figure 8.
Conclusion
The four-switch buck-boost regulator can naturally be used as either a step-down
or step-up regulator without requiring any special configurations. Bench testing has verified that the newly released buck-boost µModule delivers the highest efficiency, best thermal performance, and extended current capability compared to other available buck or boost µModule regulators. Additionally, this four-switch buck-boost can be easily configured as an inverting buck-boost regulator for applications requiring a negative output. High efficiency has been confirmed through bench tests. This paper discusses the mechanism behind the momentarily reversed output voltage behaviour, offering design guidelines and solutions to address it.
For comprehensive guidance on implementing the newly released four- switch buck-boost µModule regulator, it is recommended to refer to the data sheet and the associated evaluation kit design. It is also supported by the LTpowerCAD design tool and LTspice simulation tool. These resources provide valuable insights and specifications essential for optimising the performance in diverse applications.
www.analog.com References
Jiang, Ling, Wesley Ballar, Anjan Panigrahy, and Henry Zhang. “µModule Regulator Achieves Highest Power Efficiency.” Electronic Products, October 2024.
Components in Electronics May 2025 35
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