Power Electronics

Li-Ion Chargers Automatically Select USB or AC Adapter Input

The LTC4076 and LTC4077 from Linear Technology Corp. are standalone dual-input linear battery chargers. These devices charge single-cell Li-Ion batteries from wall adapter or USB power sources. The LTC4076 and LTC4077 use a constant-current/constant-voltage algorithm for charging, with charge current programmable up to 950 mA from a wall adapter supply, or programmable up to 650 mA from a USB supply while automatically sensing the presence of voltage at each input. The LTC4076 features programmable C/x charge current termination, while the LTC4077 offers fixed C/10 termination. The LTC4076 features a choice of fixed C or C/5 USB charge current for low-power USB operation (via the HPWR pin) and the LTC4077 offers programmable C or C/x low-power USB charge current (via the HPWR pin). Applications include PDAs, MP3 players, digital cameras, lightweight portable medical and test equipment, and large color screen cell phones.

The LTC4076 and LTC4077 feature final float voltage accuracy of 0.6% and are equipped with a patented thermal regulation scheme that maximizes the charging rate without the risk of overheating. The devices are extremely flexible with the following features programmable via a single resistor: wall adapter supply charge current, USB supply charge current and charge termination currents. As standalone chargers, they also feature trickle charge for battery pre-conditioning, undervoltage lockout, automatic recharge, a charge status indicator and "power present" status outputs to indicate the presence of wall adapter or USB power.

The LTC4076 and LTC4077 are offered in a low profile (0.75 mm) 10-lead 3-mm × 3-mm DFN package. The total solution footprint is less than 25 mm² since no external MOSFET, sense resistors or blocking diodes are required. To preserve battery energy, the LTC4076 and LTC4077 draw less than 6 uA from the battery terminal in standby and less than 2 uA in shutdown mode. Pricing begins at $1.88 each for 1000-piece quantities.

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