User Manual

SECTION 1: THEORY OF OPERATION
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VLogic and Digital Ground
The VLogic and Digital Ground section consists of a pulse-width modulation (PWM) step-down DC-DC
converter (U20) that provides an adjustable output. It also reduces noise in sensitive communications
applications and minimizes drop out voltage.
An external Schottky diode (D2) is required as an output rectifier to pass inductor current during the
second half of each cycle to prevent the slow internal diode of the N-channel MOSFET from turning on.
This diode operates in pulse-frequency modulation (PFM) mode and during transition periods while the
synchronous rectifier is off.