The ADP2503/ADP2504 are high efficiency, low quiescent current step-up/step-down dc-to-dc converters that can operate at input voltages above, below, or equal to the regulated output voltage. The power switches and synchronous rectifiers are internal to minimize external part count. At high load currents, the ADP2503/ADP2504 use a current-mode, fixed frequency PWM control scheme for optimal stability and transient response. To ensure the longest battery life in portable applications, the ADP2503/ADP2504 have an optional power save mode that reduces the switching frequency under light load conditions. For wireless and other low noise applications where variable frequency power save mode may cause interference, the logic control input sync forces fixed frequency PWM operation under all load conditions.