AN857 Datasheet, PDF (5/6 Pages) Silicon Laboratories – SINGLE-CELL REGULATED Q-PUMP DRAWS LOW QUIESCENT CURRENT

AN857
Figure 3. Modified First Stage with Synchronous Rectifier
A NOR-based logic circuit provides non-overlapping gate drive signals to the synchronous switch. The goal is to be
certain that the MOSFET gate is never driven high when the flying cap is high. The amount of dead time is set by
the 1 M x 47 pF RC time constants. Here, it can be made very wide since the 1 kHz oscillator is so slow.
In conclusion, Q-pumps offer an alternative to inductor-based boost regulators, one which can dovetail nicely with
the dual nature of microcontroller loads (low-current RTC mode vs heavier but infrequent run mode). Designing Q-
pumps for low input voltages is a challenge, but one that can be met by using the right low-voltage components,
choosing sensible switching frequencies, and taking full advantage of the V-I characteristics of rectifiers. For
additional information, please refer to the TS12011 data sheet.
Rev. 1.0
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