The LM3686 is a step-down DC-DC converter with one integrated very low dropout linear regulator and a low noise linear regulator optimized for powering ultra-low voltage circuits from a single Li-Ion cell or 3 cell NiMH/NiCd batteries. It provides three outputs with combined load current up to 900 mA over an input voltage range from 2.7V to 5.5V.

The device offers superior features and performance for many applications. Automatic intelligent switching between PWM low-noise and PFM low-current mode offers improved system control. During full-power operation, a fixed-frequency 3 MHz (typ.), PWM mode drives loads from ~70 mA to 600 mA max. Hysteretic PFM mode extends the battery life through reduction of the quiescent current to 28 μA (typ.) at light load and system standby. Internal synchronous rectification provides high efficiency.

Three enable pins allow the separate operation of either the DC-DC, post-regulation linear regulator or the linear regulator alone. If the DC-DC is not enabled during startup of the post-regulation linear regulator, a parallel small pass transistor supplies the linear regulator from VBATT with maximal 50 mA. In the combined operation where both enables are raised together, the small pass transistor is deactivated and the big pass transistor provides 350 mA output current. In shutdown mode (Enable pins pulled low), the device turns off and reduces battery consumption to 2.5 μA (typ.).

The LM3686 is available in a 12-bump DSBGA package. A high-switching frequency of 3 MHz (typ.) allows the use of a few tiny surface-mount components. Only six external surface-mount components, an inductor and five ceramic capacitors, are required to establish a 15.66 mm2 total solution size.

DC-DC REGULATOR

• VOUT_DCDC = 1.2V to 2.5V (in 100 mV Steps - Factory Programmed)
• 600 mA Maximum Load Capability (LILO = OFF)
• 3 MHz PWM Fixed Switching Frequency (Typ.)
• Automatic PFM/PWM Mode Switching
• Internal Synchronous Rectification for High Efficiency
• Internal Soft Start

DUAL RAIL LINEAR REGULATOR: LILO

• Load Transients < 50 mV Peak Typ.
• Line Transients < 1 mV Peak Typ.
• VOUT_LILO = 0.7V to 2.0V (in 50 mV Steps - Factory Programmed)
• 70 µA Typical IQ From VIN_LILO
• 350 mA Maximum Load Capability (Large FET)

LINEAR REGULATOR: LDO

• Load Transients < 80 mV Peak Typ.
• Line Transients < 1 mV Peak Typ.
• VOUT_LDO = 1.5V to 3.3V (in 100 mV Steps - Factory Programmed)
• 50 µA Typical IQ
• 300 mA Maximum Load Capability

COMBINED GLOBAL FEATURES

• VBATT ≥ VOUT_LILO + 1.5V or 2.7V, Whichever is Higher
• 900 mA Maximum Combined Load Capability
• Operates From a Single Li-Ion Cell or 3 Cell NiMH/NiCd Batteries
• Only Six Tiny Surface-mount External Components Required (One Inductor, Five Ceramic Capacitors)
• 12–bump DSBGA
• 100 µA Iq From VBATT
• 15.66 mm2 Total Solution Size