These devices feature a logic-controlled and synchronizable, fixed-frequency, pulse-width modulation (PWM) operating mode. This reduces noise and RF interference in sensitive mobile communications and pen-entry applications. Asserting the SKIP pin enables fixed-frequency mode, for lowest noise under all load conditions. The MAX1901/MAX1902/MAX1904 include two PWM regulators, adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V modes. All these devices include secondary feedback regulation, and the MAX1902 contains a 12V/120mA linear regulator. The MAX1901/MAX1904 include a secondary feedback input (SECFB), plus a control pin (STEER) that selects which PWM (3.3V or 5V) receives the secondary feedback signal. SECFB provides a method for adjusting the secondary winding voltage regulation point with an external resistor divider, and is intended to aid in creating auxiliary voltages other than fixed 12V. The MAX1901/MAX1902 contain internal output overvoltage and undervoltage protection features.