The LTC3577-1 and LTC3577-4 feature a 4.1V battery float voltage for improved battery cycle life and additional high temperature safety margin, while the LTC3577 and LTC3577-3 include a standard 4.2V battery float voltage for maximum run time. The LTC3577-3 and LTC3577-4 are tailored for SiRF Atlas IV chipsets. These ICs are highly suited for portable device applications including personal navigation devices (PNDs), digital media/video broadcasting (DMB/DVBs), digital/satellite radio, media players, universal remotes, photo viewers and portable medical and industrial devices.
The LTC3577/-X’s PowerPath manager with automatic load prioritization seamlessly manages the transition between multiple input sources to power the load, while delivering up to 1.5A battery charge current from a wall adapter supply or up to 500mA charge current from a USB port. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness). The ICs instant-on operation ensures system load power even with a fully discharged battery. Autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. An overvoltage protection (OVP) controller enables up to 30V protection for the Wall/USB input, while a high temperature battery voltage reduction circuit improves battery safety and reliability. To preserve battery energy during long periods of inactivity or to reset the product in the event of a software lockup, the LTC3577/-1 contains a hard reset function enabled via pushbutton control, placing the IC into an ultra-low quiescent current state that draws < 10uA and disables all power supplies and power paths. The LTC3577/-1 can control an external high-voltage buck regulator to achieve high efficiency Bat-Track™ charging and power path control from a high voltage source, reducing power dissipation. The internal 200mOhm ideal diode, plus an optional external ideal diode controller provide a low loss power path to the load when input current is limited or unavailable. The LTC3577/-X’s three integrated synchronous buck regulators feature 100% duty cycle operation and are capable of delivering output currents of 800/500/500mA respectively, with adjustable output voltages down to 0.8V. A high 2.25MHz switching frequency allows the use of tiny low cost capacitors and inductors less than 1mm in height. Internal low RDS(ON) switches enable efficiencies as high as 95%, further maximizing battery run time. In addition, I2C-controlled Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 20uA per regulator (< 1uA in shutdown). Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple. Additional features of the LTC3577/-X include a 40V series backlight 10-LED driver with I2C controlled 60dB brightness (1000:1 dimming range) and gradation control, pushbutton on/off control with system reset, and dual 150mA current limited LDOs.