Linear Technology Corporation announces the LTC3558, an efficient, multi-function power management solution for handheld applications. The LTC3558 is a USB battery charger with dual high efficiency switching regulators. The device is ideally suited to power single-cell Li-Ion/Polymer based handheld applications needing multiple supply rails. The LTC3558’s battery charger contains a high degree of USB functionality, including 20%/100% full-scale charge current setting, a SUSP pin for shutdown/enable, and 4 different indication states on the /CHRG pin. The final battery float voltage is accurate to ±0.5%.

The USB battery charger integrates a stand-alone Li-Ion/Polymer battery charger and two high efficiency synchronous regulators – one buck-boost and one buck – and is offered in a compact low-profile 3mm x 3mm QFN package. The part includes monolithic synchronous buck and buck-boost regulators that can provide up to 400mA of output current each and operate at efficiencies greater than 90% over the entire Li-Ion/Polymer battery range. The buck- boost regulator can regulate its programmed output voltage at its rated deliverable current over the entire Li-Ion range without drop out, increasing battery runtime. Battery charge current is programmed via the PROG pin and the HPWR pin with capability up to 950mA of current at the BAT pin. The CHRG pin allows battery status to be monitored continuously during the charging process. An internal timer controls charger termination.

The battery charger employs a constant-current, constantvoltage charging algorithm and is capable of charging a single Li-Ion battery at charging currents up to 950mA. The user can program the maximum charging current available at the BAT pin via a single PROG resistor. The actual BAT pin current is set by the status of the HPWR pin.The linear battery charger can deliver up to 950mA charge current from a wall adapter supply, or up to 500mA charge current from a USB port. battery charger’s stand-alone autonomous operation simplifies design, eliminating the need for an external microprocessor for charge termination. Both switching regulators are designed to operate over the Li-Ion/Polymer range of 2.7V to 4.2V while delivering output currents up to 400mA each.

The LTC3558’s integrated synchronous buck regulator features 100% duty cycle operation, while the buck-boost regulator is capable of regulating its programmed output voltage (typically 3.3V) over the entire Li-Ion/Polymer operating range. The integrated low RDS(ON) switches enable efficiencies as high as 92%, maximizing battery run time. In addition, Burst Mode® operation optimizes efficiency at light loads with a quiescent current of only 20uA for the buck-boost and 35uA for the buck (<1uA in shutdown for each). The high 2.25MHz switching frequency allows the utilization of tiny low cost capacitors and inductors less than 1mm in height. Furthermore, the regulators are stable with ceramic output capacitors, achieving very low output voltage ripple.

The charger’s patented thermal regulation scheme maximizes the charge rate without the risk of overheating, while the NTC input allows temperature-qualified charging. To preserve battery energy, the LTC3558 draws < 3uA from the battery in suspend mode. The charger is compatible with inputs up to 5.5V (7V absolute maximum transient for added robustness). The benefi t of the LTC3558 battery charger thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions.

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