LM3687 Datasheet | National Semiconductor

Description The LM3687 is a step-down DC-DC converter with an integrated low dropout Linear Regulator optimized for powering ultra-low voltage circuits from a single Li-Ion cell or 3 cell Ni MH/Ni Cd batteries. It provides a dual output with fixed output voltages and bined load current up to 750m A in post .. regulation mode or 1100m A in independent mode of operation, over an input voltage range from 2.7V to 5.5V. There are several different fixed output voltage binations available (refer to table 'Voltage Options'). The Linear Regulator being driven from the fixed output voltage of the buck converter (post regulation) translates to high efficiency. The device offers superior features and performance for mobile phones and similar portable applications with plex power management systems. Automatic intelligent switching between PWM low-noise and PFM low-current mode offers improved efficiency over the full load current range. During full-power operation, a fixed-frequency 1.8MHz (typ.) PWM mode drives loads from ~80m A to 750m A max. Hysteretic PFM mode extends the battery life through reduction of the quiescent current during light loads and system standby. The LM3687 also features internal protection against overtemperature, current overload and under-voltage conditions. Two enable pins allow the separate operation of either the DC-DC or the Linear Regulator alone or both. If the power input voltage for the Linear Regulator VIN_LIN is not sufficiently high (e.g. the DC-DC converter is not enabled or starting up) a startup LDO supplies the Linear Regulator Output from VBATT for 50m A rated load current (Startup Mode). If VIN_LIN is at the required voltage level, the startup LDO is deactivated and the main regulator provides 350m A output current. In shutdown mode (Enable pins pulled low) the device turns off and reduces battery consumption to 0.1µA (typ.). The LM3687 is available in a tiny, lead-free (NO PB) 9-bump micro SMD package. A high switching frequency of 1.8MHz...